Causes and Control of Wood Decay

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Causes and Control of Wood Decay,

Degradation & Stain


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ContentsMoisture .................................................................................3Wood Degradation: Causes and Control..............................4 Weathering ......................................................................................................4 Naturally Decay-resistant Species ...........................................................5

Wood Decay ...........................................................................5 Dealing with Decay ...................................................................................... 6

Stains ......................................................................................7 General Stain Control ................................................................................... 9

Insects .................................................................................. 10 Insects of Moist Wood ...............................................................................10 Pests of Dry Wood .......................................................................................12 Marine Wood Borers ...................................................................................15

Preservative Treatments .................................................... 17 Oil-type Preservatives ................................................................................17

Waterborne Preservatives ........................................................................18 Treatments for Wood Composites .........................................................20

Precautions with Preservative Treatments ....................... 20 Use-site Precautions ...................................................................................20 Handling Precautions ................................................................................21

Selection of Pressure-treated Wood ................................. 21 Over-the-counter Preservatives .............................................................23

Installation and Inspection Tips ........................................ 23

Conclusions ......................................................................... 25


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Causes and Control of

Wood Decay,

Degradation& Stain

Our society depends on wood for a varietyof uses. As population increases, so does ourneed for wood. Steel, concrete and aluminumare some alternatives to treated wood in cer-tain applications, but they have higher materialcosts, higher energy requirements in the pro-duction process, greater air and water pollutionor environmental protection costs, and greaterdependency on foreign sources for materials.

Substitute materials may not be appropri-ate for some uses. For example, some types of

steel may corrode; concrete may deteriorate insalt water; and plastic may not have the neces-sary strength, durability and structural integ-rity. Wood is a renewable natural resource that,if properly treated, maintained and placed inservice, will last indenitely. It is critical for usto use our wood resource efficiently.

Tis publication is intended to increaseyour knowledge of the causes and control ofwood decay, degradation and stain. A commoncause for replacing wood structures is decayor degradation. Wood decay and most insectproblems can be prevented for years by proper-ly using and protecting wood. Te heartwoodof some species, such as black locust and Osageorange, also has a unique chemical composi-tion that makes it very durable.

wo common terms used to describewood features are heartwood and sapwood.Heartwood is wood in the inner section ofa log and is entirely composed of dead cells.Tis region has a higher concentration ofextractives (phenolic-based compounds that

make heartwood more decay resistant thansapwood). Sapwood is wood near the bark andis often lighter in color than heartwood. Nutri-ent translocation occurs only in sapwood. Al-though most wood species can be treated witha preservative, certain species are considereddifficult to treat because of their permeabilityand anatomical features. Douglas r, a westernspecies, has below-average permeability andis classied as difficult to treat. Species suchas white oak have inclusions in the vessels

called tyloses. Tese inclusions also decreasepermeability and make treating more difficult.In general, lumber that has a high percentageof heartwood or is improperly seasoned willbe more difficult to pressure treat. Southernyellow pine (SYP) characteristics make it use-ful for many applications and easily treatable.Most pressure-treated lumber in the South isSouthern yellow pine.

MoistureIt is commonly believed that wood shrinks

as it loses moisture and swells as it gains mois-ture. Tis is partially true. Actually, wood willchange dimension only between two precisemoisture conditions. One condition is whenthe wood is void of moisture. Tis is termedthe ovendry condition. Te second conditionis when the wood bers are saturated withmoisture. Tis point usually occurs at about30 percent moisture content for most Louisi-ana species. As wood is dried from an originalgreen condition, sometimes more than 100percent moisture content, moisture is rst lost


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from the cell cavities. No shrinkage will occuruntil the wood reduces to a moisture contentof about 30 percent (ber saturation point). Ifdrying continues below 30 percent moisturecontent, water is removed from the cell wallsand shrinkage occurs. Te amount of shrinkageor swelling depends on the species, density andboard direction.

Pressure treatment with waterborne pre-servatives raises the moisture content abovethe ber saturation point, and shrinkage willoccur as the wood dries down to its in-servicemoisture content. In many applications, suchas deck boards, this shrinkage is not a majorconcern. When dimensional stability is critical,it is imperative that the lumber be kiln driedafter treatment (KDA ). Any KDA lumberyou buy should be kept under a roof or at leastunder cover and off the ground.

Te dimensional stability of different woodspecies is affected by width and density differ-ences between earlywood and latewood in thegrowth rings. For example, in species havingwide, dense latewood bands and low-densityearlywood bands, the differential shrinkingand swelling of the bands with changes inmoisture content can cause large stresses inthe wood that can result in raised grain anda defect known as shelling. Raised grain willtend to be more pronounced on at grainedlumber. Shelling is an extreme case of raised

grain in which thelatewood bandsseparate from theearlywood bandsto form a knife-like or spearlikeedge. Tis is onereason why decklumber is oftenrecommended tobe placed pith-side down (or

bark-side up). Ifthe two sides of aparticular boardare of equal qual-

ity, its better to place the board bark-side up. If,however, the pith side is clearly the better side,place this side up.

Moisture greatly affects lumber in use andcan quickly lead to deterioration. Moisture canalso allow wood to be attacked by insects, hin-

der the performance of nishes and paints, ainduce surface stains.

Wood Degradation:Causes and Control

Wood degradation is not the same as wodecay. Te three primary sources of wood degradation are fungi (decay or rot), insects and

weathering. In addition, re can also degradewood. Te organisms that decay wood havefour basic requirements: moisture (generallyto 100 percent of dry-wood weight), oxygentemperature (generally between 50 degrees a95 degrees Fahrenheit) and food (the wooditself ). We can control wood degradation byaltering one or more of these requirements. Asawmill will often keep its logs moist undersprinkler system to saturate the logs with waand create an anaerobic environment in whicthere is insufficient oxygen for most wood d

cay organisms and insects. Wood can undergslow bacterial degradation in fresh water or attacked by marine borers in brackish or saltwater, however.

It is impractical for consumers to keeplumber under a sprinkler system or buried inmud! Most wood decay can be prevented bysimply keeping the wood dry. If lumber is drto 6-8 percent moisture content for indoor usor 15-18 percent for outdoor uses, it shouldnot decay if the moisture content is maintainbelow 20 percent. A common cause of wooddecay is when untreated wood is alternately posed to wet and dry conditions, as in grouncontact, or when it collects moisture and re-mains moist for an extended period. o prevethis situation, either keep your untreated lumber dry or use treated wood if you suspect itwill get wet in service. Be sure to use pressutreated lumber approved for ground contact you are building a structure that requires oneend of some boards to be in contact with soiand moisture.

WeatheringTe surface of wood can be degraded if

the wood repeatedly becomes wet and dry, isexposed to high and low temperatures and isexposed to direct sunlight. Tis degradationcauses roughening of the surface, checking,splitting and wood cell erosion. Erosion, cauby the loss of wood cells from the lumber suface, is a slow process (Figure 1).

Figure 1. Severe weathering oc-curred on the surface of these treatedsouthern yellow pine boards used to

construct a boat dock. Most docks arecontinually exposed to wet and dry

conditions and direct sunlight. It is rec-ommended to brush apply each year awater repellent that also protects from

ultraviolet (UV) degradation of thewood surface.


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water repellant to prevent brown rot on woodused outside. Te appearance of any mush-room-like bodies, which is an indication ofadvanced wood decay and substantial strength

loss, is important for the consumer (Figure 5).Brown-rotted wood will develop a reddish-brown color and have a charred appearance. Italso displays more than average shrinkage upondrying and is friable (soft).

White rotWhite-rot fungi attack is commonly ob-

served on hardwoods. White-rotted hardwoodundergoes little surface alteration, develops awhite or bleached appearance, displays near-normal shrinkage and in the early stages ofdecay is solid to the touch rather than friable.Tese fungi attack cellulose, hemicellulose andlignin, but deterioration is slower than thatwith brown-rotted wood.

Soft rotSoft-rot fungi affect wood exposed to long-

term moist conditions. Te wood is darkenedand appears dull brown or blue-gray, and thesurface can easily be scraped off with a probe.

Soft-rot fungi display considerable varia-tion in

their ef-fects oncell wallchemicalconstitu-ents dur-ing decaydevelop-ment. Formany spe-cies, theprincipal

food source is the carbohydrates in wood, busome remove more lignin than carbohydrateLignin is the natural glue in wood that holdsadjacent cells together. Soft rot is often con-fused with white rot because of their similarappearance. Figure 6 shows typical surfacechecking of soft-rotted wood when dry. Oilpreservatives are recommended for protectiofrom soft-rot fungi.

ControlRot-inducing fungi can be stopped by

removing one of the four elements necessaryfor the fungi to live (1) proper moisture, (2)oxygen, (3) food and (4) temperature. Onlyone of these elements needs to be removed tprevent wood decay. Te simplest method isto keep wood dry. Most rot-causing fungi winot attack wood if the moisture content is lethan 20 percent. Te oxygen component canbe removed by submerging the wood in wateLogs that cannot be processed soon after feland bucking should be placed under a watersprinkler system or submerged in water. Tefood component cannot be removed, but wecan poison the food by preservative-treatingthe wood. Also, temperatures below 50 degrFahrenheit will allow negligible fungi growtand temperatures above 200 degrees Fahren-heit are lethal to fungi.

Dealing with DecaySince most decay problems are caused

by moisture, the cure is simple. Eliminate thsource of moisture. Check the roof, walls anplumbing for leaks. Go outside and check theaves and gutters. Are the eaves wide enougto prevent water from coming down the sidewalls? Are your gutters poorly maintained omissing? Be sure the foundation is not crackand the soil slopes away from the house. Do just treat the mildew, mold or decay problemYou need to eliminate the cause!

Ten, remove as much decayed wood as

is practical and economical. Tis is really im-portant with load-bearing wood members. Cback the rotted wood to the sound wood. Kein mind that difficult to detect incipient decacan extend well beyond visibly rotted areas.When a partially decayed structural membercant be replaced, reinforce it with treatedwood. Be aware that decayed wood absorbs holds water more readily than sound wood, slet rotted areas of members not removed drybefore making repairs. Consider treating infeed but otherwise-serviceable wood left in pl

Figure 4. Fungal decay of wood bybrown-rot decay fungi. (Source:

Forest Products Society)

Figure 5. Fungal fruiting bodygrowing from wood. These fungi aresometimes referred to as mushroomsor toadstools. This is evidence ofadvanced decay and serious strengthloss. This lumber is extremely danger-ous if it is used as a walking surfacesuch as a boat dock or backyard deck.(Source: Forest Products Society)


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with a water-borne, borax-based preservativethat will not only kill active fungi but guardagainst future infection as well. Borates havelow human toxicity and do not affect woodsstrength, color or nishability.

If the decay is too severe, and you want topreserve the historic or architectural characterof moldings, carvings or furniture, consider an

epoxy repair job. Epoxies consist of resin andhardener that are mixed just before use. Liq-uids for injection and spatula-applied pastesare available. After curing, epoxy-stabilizedwood can be shaped with regular woodwork-ing tools and painted. Epoxies are not preser-vatives and will not stop existing decay. Teycan be tricky to use, so follow all label direc-tions.

StainsWood-staining fungi differ from the

wood-destroying fungi in that wood-stainingfungi do not noticeably affect wood strengthor texture. Mold and stain are often consideredtogether because of the similarity of actionof the fungi on wood microstructure. Moldand stain cause little injury to the structureof wood they infest, provided that favorableconditions do not create a more advanced stagewhere it would be more appropriately consid-ered as soft rot. A number of wood-stainingfungi produce a wide range of color effects ordifferent stains.

Blue StainBlue stain, also called sapstain, is the most

economically important stain. It occurs in thesapwood of both hardwoods and softwoods.Heartwood is essentially immune to the fun-gus that causes blue stain, but the salabilityand price of blue-stained lumber are greatlyreduced because of its appearance. A naturalnish that looks good to most consumers can-not be applied to blue-stained lumber.

In Louisiana, blue stain frequently occursin SYP lumber that is not seasoned or usedquickly. All SYP lumber should be dried orchemically treated as soon as possible aftersawing. Failure to do so can result in blue stainin as little as two weeks in certain times ofthe year. Te SPIB does not specify that SYPdimension lumber be down-graded if bluestain is present, but SPIB does mandate thatSYP lumber with blue stain cannot be sold asAppearance Grade lumber. Te southern hard-woods such as yellow poplar, magnolia, tupelo

and oak arealso goodcandidatesfor blue stain.Tese species,however, canoften be airdried for alonger periodwithout therisk of stainbefore kilndrying. Bluestain may de-velop duringvarious stagesof manufacture, storage or shipping or even inthe nished product if there are sufficient con-ditions (moisture, air and temperature). Not allblue stain occurs after sawing. It can also occur

in standing trees or logs (Figure 7).Control

Control can be accomplished either byrapid drying of the wood to reduce moisturecontent or by dipping or spraying with fun-gicidal solutions. Dipping is usually fairlyinexpensive. If the risk of stain is severe, bothfungicidal protection and good drying practicesare recommended for high-grade products.Drying can be accomplished either by kiln dry-ing or air drying with proper stack placementand air ow. Since stain can be transferredfrom stained lumber to unstained, green wood,proper protection from contamination is im-portant. Terefore, dont stackstained and unstained materialtogether, especially withoutusing stickers between theboards.

Chemical StainIn addition to discol-

orations produced by fungi,wood is also subject to certainother stains that result fromchemical changes in woodcell walls. Te nature andcauses of these changes are notdenitely known, although,in some cases at least, theyinvolve enzymatic or non-enzy-matic oxidation of certain organic compoundslargely conned to sapwood. Such stains arefound in both softwoods and hardwoods.Tey sometimes appear in logs that have been

Figure 7. Blue stain is often referred toas sapstain because it tends to occurin the sapwood of logs and lumber.The lumber cut from this southern yellow pine log will contain blue stainbecause it is already present in the log.(Source: Forest Products Society)

Figure 6. The surface of soft-rot woodappears as if it was lightly charred,and there are often cracks alongand across the grain. (Source: ForestProducts Society)


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prevent direct rainand place woodhigh enough offthe ground to pre-vent rain splashingor ooding.

InsectsMany insects

destroy wood.Te three mostimportant insectsfor the wood userto be aware of aretermites, beetlesand carpenter ants.Tree categoriesof insects attack

wood. First, pests of moist wood are insectsthat attack improperly protected lumber and

usually attack together with wood-destroyingfungi. Second, pests of dry wood are insectsthat can attack dry wood. Tese dry woodinsects do not attack in association with wood-destroying fungi and are capable of reinfestingthe same piece of wood. Tird, marine borersare not insects but are mollusks and crusta-ceans that infest wood in salt water, destroyingpilings, ships and boats.

Insects of Moist WoodSome insects attack trees or wood that is

partially moist as a result of contact with theground or becomes wet from faulty construc-tion, improper maintenance or previous insectactivity. Tese insects are usually associated

with protozoa, fungi and bacteria that aidthem by converting the cellulose and lignin inthe wood into materials that are more digest-ible. Because of these microorganisms, moist

and decaying wood provides suitable food ashelter for these insects. Some insects attackmoist wood found in living trees are also usually pests of wood products in contact with tground or another moisture source.

TermitesIn Louisiana, two groups of termites atta

wood. Native subterranean termites are the

more common (Figure 10). Tey require woodwith a moisture content of more than 20 per-cent. Tis group of termites is unique in thatthey can provide additional moisture to thewood by constructing earthen connecting tubto wood that is not in contact with the grounTerefore, if untreated wood is to be placedoutside in moist locations, it is imperative thit be placed covered above ground on blocksand not in ground contact. Te area aroundthe block should be treated for termite controSubterranean termites are found throughoutLouisiana (Figure 11). Formosan subterraneatermites are similar to native subterranean temites but form larger colonies and have moraggressive feeding habits. Tis species wasrst discovered in exas in 1965 and has beenfound in several Louisiana port cities and incoastal areas near the Gulf of Mexico. ermitare often confused with winged ants, but theare several differences (Figure 12).

Termite ControlTe prevention and control of subter-

ranean termites are based on the same factorthat affect the growth of wood-destroyingfungi (temperature, oxygen, food and mois-ture). Te best method to prevent attack bysubterranean termites is to build woodenstructures in a manner that allows the woodto be kept dry. Structural and sanitary mea-sures will not give complete protection agaitermites, so a chemical means of protectionis often advocated. Te ideal time to install achemical barrier under a home or shed is at time of construction. But if a building becominfested, steps can be taken to dry the woodconstruct a chemical barrier between the nesand the infested wood. Also, nests and potential nesting places near the building shouldbe eliminated if they can be found. Contact reputable pest control company for assistancwhen termites attack wooden structures.

Modern styles of architecture that demancentral heat, heated basements and low foundations may be contributing factors to moreinsect pests. Tere is a tendency on the part

Figure 10. In Louisiana, subterra-nean termites were once found onlyin the southern Louisiana parishes.

They are found throughout mostof the United States. Most termites

require wood in ground contactand moist wood. Subterranean

termites are dangerous to woodbecause they can provide additional

moisture to the wood by construct-ing earthen connecting tubes to

wood that is not in ground contact.(Source: Forest Products Society)

Figure 11. This range map ofsubterranean termites shows a

very heavy population throughoutLouisiana and most of the South.(Source: Forest Products Society)


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of some builders to leave wood in a trench orunder the foundation and to throw in otherwaste materials, knowing they will be hiddenwhen backlled. Tis creates ideal conditionsfor termites. A major contributor to the sub-terranean termite attack is the lack of adequatesoil treatment prior to laying the foundation.Te outside of the slab should be treated. Also,soils under buildings should be stabilized andinstalled with drains before construction toprevent movement which can cause cracks inthe foundation and support timbers and allowmoisture to enter the building. Te importanceof drainage cannot be overstated. Louisianaresidents are advised to check with a local pestcontrol agent regarding the building codes forminimum protective practices. Also, homebuyers can specify that waste be disposed ofaway from buildings when making construc-tion plans for a new home or building.

In general, protection against subterraneantermites and decay requires that these pointsbe observed:

1. Remove all tree stumps before grading,and clean up all wood (forms, grade stakesand waste) under and around buildings beforebacklling or construction.

2. reat soil with insecticides before pour-ing foundations, and allow foundation soilsthree to six months to settle properly beforebuilding.

3. Set buildings on concrete foundationsthat have an 8-inch clearance between wooden joists and soil.

4. Buildings with crawl spaces should havean 18-inch clearance between wooden joistsand ground.

5. Grade land to slope away from thebuilding on at sites, and install drains to di-vert moisture away from buildings.

6. Wood closest to the ground or founda-

tion, especially soleplates, should be pressuretreated to at least above-ground retentionstandards. All untreated wood should be keptaway from contact with the ground or mois-ture sources

7. Prevent lumber in the home from be-coming wet from rain, leaks and condensation.Adequate ventilation must be maintained incrawl spaces. In Louisiana, at least a 24-inchoverhang is recommended to keep walls dry.

8. Inspect buildings annually for poten-

tial problems. Check plumbing, caulking neardoors and windows, and water splash areassuch as behind air conditioners.

Carpenter Ants

Carpenter ants are widely distributed inLouisiana and North America. Tey are amongthe largest ants, occurring in lengths of 12 mmor more. Tey live in a colony in which threecastes of adults are recognized: kings, queensand workers. In the South, carpenter antsreadily infest live tulip poplar and black locusttrees attacked by the locust borer. Te tunnelsare often in the grass above ground, disgur-ing lawns in residential areas. Te presence ofcarpenter ants in residential areas can be seri-ous. Tey can burrow into wood to make nests,but unlike termites, they do not use wood forfood. Also, carpenter ants differ from termitesby making galleries that yield complete accessacross annual rings between the galleries (Fig-ure 13). rees with butt scars may be weak-ened by the ants galleries and, with time, maybe subject to wind throw.

Carpenter Ant ControlCarpenter ants can nest in houses without

attacking wood by using existing voids or even

Figure 12. Winged termite and wingedant comparison. (Source: Moore 1979)


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termite galleries in wood. Carpenter ants forag-ing for food and water are generally more ofa nuisance than a danger in houses. Te samegood building practices to minimize termiteinjury will also help to control carpenter ants.If you nd carpenter ant nests in the house,treat the nests, approaches and surroundingareas with a residual contact insecticide (dustor spray). A pesticide specically registeredfor treating indoors must be used in the housetreatment. Te infested wood can be boredbefore injecting the pesticide and plugging theholes. It is ineffective to treat only areas wherethe ants are seen, because many do not leavethe nest.

Powder-post BeetleTe most economically important of the

wood-attacking beetles are the powder-postbeetles. Te anobiid beetles and the lyctidbeetles are the two most common powder-postbeetles. Te anobiid beetles are often calledthe death-watch beetles because of the tappingsound adults make with their heads as a mat-ing signal. Tis sound was probably rst heardby an individual sitting in a quiet room with avery ill person. Tese beetles primarily attacksapwood but will also destroy heartwood (Fig-ure 14). Tey digest the cellulose component ofthe cell wall at a moisture content of 15 percentand above. Lyctid beetles are also commonly

called powder-post beetles and prefer woodthat has a moisture content of more than 20percent or wood that has already been deterio-rated by another organism. Lyctid beetles area serious pest to the sapwood of hardwoods.

Wood with large pores such as oak, hickoryand ash are most susceptible, but species sucas yellow poplar, sweet gum and cherry can be infested. Most activity occurs with a woomoisture content between 10 percent and 20percent, but attacks can occur with a woodmoisture content of 8-32 percent.

Powder-post Beetle Control

Control for powder-post beetles requiresone of three approaches: (1) eliminate or re-duce the beetle population, (2) use a chemicatreatment to protect susceptible wood or usenatural decay- resistant wood or (3) control environmental conditions in the wood to stodevelopment of larvae.

Proper construction techniques will alsohelp control power-post beetles (see the 8items under termite control). Constructionpractices that use pressure-treated wood in

hazardous areas will help prevent beetle at-tack. A diffusion treatment that includes borwill also stop attacks. A residual insecticidecan be brushed or sprayed to control beetles.A sulfuryl uoride fumigant can also be useto stop beetle attacks on wood in storage or service. Tis is a good method if the infestatiois extensive or if other methods are impractiFumigation is an expensive process and wheperformed indoors requires residents to leavfor one or more days. It is sometimes used inconjunction with a home sale to certify that

structure is insect-free, but it does not guaratee long-term protection.Powder-post beetle control can also be

achieved through proper wood use. Rapiddrying of sawn lumber is essential to contropowder-post beetles and many other wooddeterioration problems in green lumber. Tesebeetles can attack lumber that is being air-dried because of the slow nature of the proceAlso, these beetles attack lumber that has beair-dried in Louisiana because most air-driedlumber will reach equilibrium moisture cont(simply stop losing moisture) when the lum-ber reaches 12-15 percent moisture content.Another method for avoiding favorable condtions for insect larvae and eggs is to subject wood to extreme heat (such as in a dry kiln)extreme cold.

Pests of Dry WoodLyctid Beetle

In general, wood-destroying beetles attain the larval stage. Te most common species

Figure 13. Carpenter ant damageto wood is different from termite

damage because the former shows a preference for earlywood but removes

some latewood to allow accessbetween galleries. (Source: Forest

Products Society)


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infesting dry hardwoods is the southern lyctidbeetle, which occurs throughout the UnitedStates. Tese beetles are pests of hardwoodspecies, particularly ash, hickory, oak and wal-nut that has usually have been in service forless than 10 years. Beetles prefer these speciesbecause of their starch content and pore size.Te starch content provides an excellent foodsource, and the large pore size allows for easymovement within the wood. Te attack is usu-ally conned to the sapwood because of thehigher extractive content and greater naturaldecay resistance in the heartwood (Figure 15).Occasionally, infested ooring may be installedwithout the carpenter or home owner real-izing the wood is not sound. It is often notuntil the beetles emerge in the spring that theirunwelcome presence is recognized. Furnitureand cabinet work can be attacked if there is alag between construction and nishing. In the

spring, furniture may be peppered with small,round exit holes that denote adults leaving thewood. Lyctid beetles have also been found inplywood panels and products made from ply-wood.

Lyctid Beetle ControlTe injury caused by lyctid beetles can be

prevented by denying the insects the time andplace to lay eggs. Tese beetles are primarilypests of new hardwood lumber; infestationsare rare in dry wood in use for more than veyears. Prevention is the keynote of lyctid beetlecontrol because wood infested by these insectsis typically only t for rewood. In lumber-yards or secondary processing plants wherelarge quantities of hardwood stock are kepton hand, wood should be inspected fre-quently. An infestation is usually indicatedby small quantities of ne borings (powder)that sift out of infested pieces. Rapid use willgreatly reduce the chance of an expandinginfestation in storage sheds. Woodworkersshould always use the oldest stock rst. Te

simple rule for processing lumber is: rstin, rst out. Keep waste wood separate, andburn or haul it away to be disposed of prop-erly. Tere are no circumstances in whichwaste wood should be allowed to accumu-late near buildings and serve as a breedingground for wood-destroying beetles!

One of the most effective means of pro-tecting wood from lyctid beetles is with asealer such as linseed oil, varnish, paraffin orpaint. Tese sealers will close the pores and

prevent deposit of eggs in the pores of wood.Millwork should not be treated with a waxsealer because it can affect nishes.

Anobiid BeetleTe anobiid beetles feed on both sapwood

and heartwood of softwood and hardwood butusually are found in standing trees. Only a fewspecies of this beetle attack wood products.Most infestations develop slowly and are usu-ally not detected until after several generationsof adults have emerged.

Anobiid Beetle ControlDamage from anobiid beetles can best be

prevented by using dried or treated lumberand avoiding humid conditions by maintainingadequate dry air ventilation, especially withincrawl spaces.

Figure 14. Anobiid beetle exit holes areround and vary in diameter from 1/16inch to 1/8 inch. Zone lines on the endgrain also indicate wood decay is pres-ent. (Source: Forest Products Society)

Figure 15. Ash shovel handle damagedby lyctid beetles. Exit holes are 1/32inch to 1/16 inch in diameter. (Source:Forest Products Society)


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Bostrichid BeetleTese beetles attack partially seasoned

hardwoods and conifers while the bark is stillon the wood. Te emerging beetles are oftenfound associated with recently made bark-cov-ered furniture and timbers, rewood that hasbeen brought indoors and recently processedwood that was not kiln dried or treated. Te

most common species in the eastern UnitedStates infests hickory and persimmon.

Bostrichid Beetle ControlInfestation by bostrichid beetles can be

prevented by the prompt use of hardwood logsand lumber and the rapid debarking of woodused for sheathing, rustic furniture and housetimbers. Preventing the emergence of thesebeetles from rewood in the home can be read-ily achieved by burning dry wood immediatelyor by stacking it out of doors before burning.

Long-horned BeetlesWood-damaging long-horned beetles are

named because their antennae are longer thanhalf of their body length in adults. Te larvaeare known as round-headed wood borers be-cause of their circular emergence holes (Figure16). Te injury is sometimes mistaken for thatof power-post beetles. Damage from these

beetles is usuallyconned to re-,disease- or insect-killed timber thatwas salvaged orimproperly airdried. Te beetlesinjure the woodbefore it is pro-cessed and stoponce it is dried.Long-hornedbeetles are in thewood only a limit-ed time and do notreinfest the wood.Tey are not con-sidered a seriousstructural pest.

Long-horned Beetles ControlTe best method of long-horned beetle

control is rapid wood use. imber salvage oper-ations need to be conducted as quickly as pos-sible. Since trees killed by insects, re or diseaseare ideal hosts for long-horned beetles, rapidmilling and drying of the lumber are critical.

Kiln drying will control eggs, larvae and aduTey are not a problem with dry lumber.

Old House BorerTe old house borer is a beetle that has

spread from Europe throughout the world. Itwas introduced into the United States morethan 100 years ago. It prefers freshly sawn swood lumber, but its presence is usually not

detected for several years because of its longcycle. Te symptoms of the initial infestationinclude the distinct sound of larval feeding, occasional small amount of boring dust and blistering of the wood surface. Teir presencecan be readily veried by probing the galler-ies and softened areas for larvae. Adults areoften found against window screens within thouse, especially in the attic.

Old House Borer ControlTe old house borer can usually be pre-

vented from damaging wood by using kilndried or treated lumber that has been properlstored and kept dry while in service. Severeinfestation will often require the replacemenof the infested pieces. Occasionally, an entirhouse will be infested, possibly indicating ththe wood was infested before construction.When a large infestation occurs, fumigation recommended. Small areas can be treated bypest control company.

Carpenter Bees

Carpenter bees are found throughoutmuch of the southern and eastern UnitedStates and resemble bumblebees except thatthey have smooth and shiny (rather than hairabdomens and no pollen baskets on the hindlegs. Although carpenter bees are usually noserious pests, their tunnels can be damagingthe bees infest the wood annually for nesting(Figure 17). Te original entry hole is perfectlround and approximately inch in diameterTe tunnel turns at a right angle after penetrating the length of the bees body and runs acr

the grain of the wood. In Louisiana, all specof wood may be attacked, but cypress, pine cedar are preferred.

Carpenter Bees ControlControl of the carpenter bee can be acco

plished by placing an insecticide in the tunnthat the female has made to lay her eggs in twood. Control can also be accomplished bypainting or treating with borates. Wood pres-sure treated with preservatives such as boraxor high retention levels of water-borne prese

Figure 16. Long-horned beetle orround-headed wood borer dam-

age to ash. Note the grub-shapedentrance hole on top and the round-

oval exit hole on bottom. (Source:Forest Products Society)


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vatives is resistantto attack. Applyinga surface coating ofpreservatives mayalso be helpful. In-terior, unpaintedwood surfaces can beprotected by keepingwindows and doorsclosed or screenedduring the spring andearly summer to pre-vent bees from nest-ing in your house.

Drywood Termites

In Louisiana, these termites are foundstatewide. Drywood termites are extremely se-rious pests in the tropics and can attack woodwith as low as 13 percent moisture content.Tey can enter buildings through unscreenedair vents and over time can cause substantialinjury with little evidence of their activity.Tey require no contact with the ground. Dry-wood termites will attack areas of wood wherepaint has peeled away, and they can even chewthrough several types of coatings! Teir pres-ence is indicated by the softening of the wood,blistering of the wood surface, the faint soundof moving termites and the piles of fresh, six-sided pellets ejected from infested wood.

Drywood Termite ControlDrywood termites can be serious pests

(Figure 18). Te rst step in protection isproper construction techniques, with tight joints, wide roof overhangs and all wood pieceskept dry. Tis should be followed by thoroughsealing or painting of all exposed sur-faces. Moreover, all painted surfacesshould be repainted often enough tomaintain a protective covering overthe wood. Back-painting (paintingthe interior surface) of siding andwood trim with a primer coat ofpaint or a wood preservative is use-ful in the prevention of attack bydrywood termites. Be alert to detectinfestation in the early stages whenit is easier to control. Badly injuredtimbers will need to be replaced.Fumigation and borates are twotreatments for control of drywoodtermites.

General Drywood Insect ControlTe rst step in controlling the numerous

species of insects that infest seasoned wood isthe correct identication of the insect. Correctidentication is critical because the rate andextent of injury vary with species, and specictreatments are required for specic insect in-festations. A pest control entomologist or LSUAgCenter entomologist can help with insectidentication and control.

Marine Wood BorersTe control of any marine borer depends

on proper species identication. As mentioned,wood can be maintained free of decay by sub-merging the wood in water and thus depletingthe oxygen requirement for many wood-de-caying organisms. Tis method prevents mostinsect injury but promotes injury by marinewood borers. Wood placed in a marine envi-ronment, such as boat docks, must be treatedwith a marine preservative. Creosote is some-

Figure 17. Carpenter bee damageshowing a single entry hole (from in-side) at the top center and individualcells (right) formed by the bees.(Source: Forest Products Society)

Figure 18. Example of drywoodtermite damage.


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times insufficient against some types of marinewood borers. In these cases, the wood must beprotected with creosote and an inorganic arsen-ical in a process known as dual treatment. Tisis absolutely critical for the long-term integrityof the structure in these hazardous conditions(Figure 19).

ShipwormsShipworms will attack any untreated wood

submerged in salt water. Te greatest injury is

done to pilings and wooden boats. Untreatedpilings may last less than a month in the Gulfparishes. Te replacement cost of pilings de-stroyed annually by shipworms is tremendous.Tese animals prefer warm salt waters. More

than one-half of the volume of a pile may eaily be destroyed without any evidence of injbeing apparent on the piles surface. Only bycutting into the piling can its condition be ascertained. Te greatest damage in a piling usually occurs just above the mud line, althoughentrance holes may be found throughout thesubmerged area. Entrance holes about 1/16inch in diameter are bored into the surface othe wood by the larvae (Figure 20).

Shipworms ControlMetal sheathing around a piling is effec-

tive but expensive and not very durable, un-less its galvanized or made from noncorrosimetals. Cement casings are unsatisfactorybecause cracks develop as a result of expan-sion, contraction and wave action. Plastic anberglass coatings have been used with somsuccess. A very successful method of protecing piling against shipworms is impregnatiowith marine-grade creosote treatments of 20to 25 pounds per cubic feet (pcf). Also, 2.5 of wood of chromated copper arsenate (CCAor ammoniacal copper zinc arsenate (ACZAmay be used. Surface treatment is not suf-cient, so the preservative must be pressureapplied to obtain good penetration. Deep penetration is difficult if not impossible with madense hardwoods. A softwood, such as Southern yellow pine, with a wide sapwood zone ipreferred. Applying marine creosote is still tpreferred treatment. Noncorrosive metal capand coverings on pilings are benecial becauthey protect against structural injury and en-trance of shipworms.

LimnoriaLimnoria is the genus commonly known

as gribbles, and they do considerable dam-age along coastal waters (Figure 21). Tey areconned to clear salt water and cannot endufresh to turbid water. Tey can tolerate lowtemperatures. When these crustaceans attacka piling, their tunnels almost touch, so the thwalls between them are quickly worn awayby wave action, leaving a new surface of woready for reinfestation.

Limnoria ControlTe protection of wood from Limno-

ria attack is much more difficult than fromshipworms. Some species are resistant tocreosote, partially because of the deteriora-tion and leaching of creosote in warm waterTe use of certain copper salts (chromated

Figure 19. Utility poles and pilings

in salt water require protectionfrom marine wood borers. In somemarine areas, the wood must be

treated with an inorganic arsenicalin addition to creosote.

Figure 20. Shipworm damage on pil-ings is usually at the mud line. Larvae

enter the wood at right angles tothe grain and burrow with the woodgrain along an irregular course. Thewood often becomes honeycombed

such as this piece. (Source: ForestProducts Society)


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copper arsenate and ammoniacal copper zincarsenate) provides effective protection fromLimnoria attack. A heavy retention (2.5 pcf)of CCA or ACZA works well. Copper or tinsalts, fungicides and insecticides, especially thechlorinated hydrocarbons added to creosote,have shown various degrees of effectiveness inpreventing Limnoria attack, but their use islimited by environmental regulations. In areaswhere severe attack by both types of marineborers is present, or if creosote-resistant spe-cies of Limnoria are present, use a dual treat-ment. Tis method calls for pressure treatmentwith the copper salt (1.0 to 1.5 pcf of CCAor ACZA) followed by a pressure treatmentwith marine-grade creosote (20 pcf). Mov-able wooden structures and boats can also beprotected by an unbroken covering of marinepaint. When borers have gained entrance towooden vessels, they can be killed by running

the boats into fresh water or dry dock for atleast 30 days.

Preservative TreatmentsFactory-applied preservatives fall into two

general classes: those with an oily nature, suchas creosote and petroleum solutions of pen-tachlorophenol, and those that are dissolved orsuspended in water and applied as water solu-tions. Te main difference is the type of liquidused to carry the toxic chemicals into the woodstructure. Heavy oil preservatives have some

advantage in extremely wet situations, sincebesides being toxic to fungi, the liquid car-rier retards liquid water movement. A seriousdrawback to the oil-based treatments is thatthe wood surface is oily and difficult to nishor paint. It is possible to use light organic sol-vents as the carrier for toxic compounds so thewood may be painted after treatment. Tesesolvents evaporate rapidly, leaving the woodwith an untreated appearance.

Wood preservatives also are classied orgrouped by the type of application or exposureenvironment in which they are expected toprovide long-term protection. Some preser-vatives have sufficient leach resistance andbroad-spectrum efficacy to protect wood thatis exposed directly to soil and water. Tese pre-servatives will also protect wood exposed aboveground and may be used in those applicationsat lower retentions (concentrations in thewood). Other preservatives have intermediatetoxicity or leach resistance that allows themto protect wood fully exposed to the weather,

but not in contact with the ground. Other pre-servatives lack the permanence or toxicity towithstand continued exposure to precipitationbut may be effective with occasional wetting.Finally, some formulations are so readily leach-able that they can only withstand very occa-sional, supercial wetting

Oil-type PreservativesTe most common oil-type preservatives

are creosote, pentachlorophenol, and coppernaphthenate. Conventional oil-type preserva-tives, such as creosote and pentachlorophenolsolutions, have been conned largely to usesthat do not involve frequent human contact.Te exception is copper naphthenate, a preser-vative that was developed more recently andhas been used less widely.

Wood will not swell from the applicationof preservative oils, but it may shrink if it loses

moisture after the treating process. Creosoteand solutions with heavier, less-volatile petro-leum oils often help protect wood from weath-ering, but they may adversely inuence itscleanliness, odor, color, paintability, gluabilityand re resistance. Wood treated with heavyoils should never be used inside residences orother enclosed, inhabited structures. Volatileoils or solvents with oil-borne preservatives,if removed after treatment, leave the woodcleaner than the heavier oils but may not pro-vide as much protection. Wood treated with

Figure 21. These boat dock pilingshave been heavily damaged by marineborers, commonly known as gribbles(Limnoria). (Source: Forest ProductsSociety)


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some preservative oils can be glued satisfacto-rily, although special processing or cleaning maybe required to remove surplus oil from surfacesbefore spreading the adhesive. Oils tend to re-tard wood moisture absorption, but waterbornechemicals do not unless they are additionallytreated with a water repellent. High grade,water-repellent, pressure-treated lumber is nowavailable.

CreosoteCreosote is a commonly used oil-type

preservative. Because its a mixture of many dif-ferent organic chemicals in various percentages,it is toxic to many wood-destroying organisms,including Formosan and subterranean termites.For many years, either coal tar or petroleumoil has been mixed with coal-tar creosote invarious proportions to lower preservative costs.Tese creosote solutions perform satisfactorily,particularly for poles, posts and crossties wherethey have been most commonly used. Coal-tarcreosote has the advantages of (1) high toxic-ity to wood-destroying organisms; (2) relativeinsolubility in water and low volatility, whichimpart to it a great degree of permanenceunder the most varied conditions; (3) ease ofapplication; (4) ease with which its depth ofpenetration can be determined; (5) low cost;(6) long record of satisfactory use. Creosoteemits an unpleasant odor that can harm peopleand plants. Foodstuffs sensitive to odors shouldnot be stored near creosote-treated material.Creosote can also burn the skin of some people.Freshly creosote-treated timber can be easilyignited and will burn readily. After the treatedwood has seasoned for several months, its easeof ignition is reduced.

PentachlorophenolPentachlorophenol has been widely used as

a pressure-treatment preservative in the UnitedStates since the 1940s. Te active ingredients,chlorinated phenols, are crystalline solids thatcan be dissolved in different types of organicsolvents. Te performance of pentachlorophe-nol and the properties of the treated wood areinuenced by the properties of the solvent. Pen-tachlorophenol is effective when used in groundcontact, fresh water or above ground. It is notas effective when used in seawater. Te heavy-oil solvent, as specied in AWPA Standard P9,ype A, is preferable when the treated woodis to be used in ground contact. Wood treatedwith lighter solvents may not be as durable.

Wood treated with pentachlorophenol inheavy oil typically has a brown color and mahave a slightly oily surface that is difficult topaint. It also has some odor, which is associawith the solvent. Pentachlorophenol in heavyoil should not be used when frequent contacwith skin is likely (handrails, for instance).Pentachlorophenol in heavy oil has long beepopular choice for treating utility poles, bridtimbers, glue-laminated beams and foundatipilings. Te effectiveness of pentachlorophenis similar to that of creosote in protecting bohardwoods and softwoods, and pentachloro-phenol often is thought to improve the dimensional stability of the treated wood.

Copper NaphthenateCopper naphthenate is effective when

used in ground contact, water contact or aboground. It is not standardized for use in salt-water applications. Copper naphthenates ef-fectiveness as a preservative has been knowsince the early 1900s, and various formulatiohave been used commercially since the 1940It is an organometallic compound formed asa reaction product of copper salts and naph-thenic acids derived from petroleum. Unlikeother commercially applied wood preservatismall quantities of copper naphthenate can bpurchased at retail hardware stores and lum-beryards. Cuts or holes in treated wood can btreated in the eld with copper naphthenate.

Wood treated with copper naphthenatehas a distinctive bright green color that weaters to light brown. Te treated wood also hasan odor that dissipates somewhat over time.Depending on the solvent used and treatmenprocedures, it may be possible to paint woodtreated with copper naphthenate after it hasbeen allowed to weather for a few weeks.

Copper naphthenate can be dissolved in variety of solvents, but for pressure treatmenit is usually dissolved in a heavy oil. Coppernaphthenate is listed in AWPA Standards fortreatment of major softwood species that areused for a variety of wood products. It is notlisted for treatment of any hardwood speciesexcept for railroad ties.

Waterborne PreservativesWaterborne preservatives react with or

precipitate in treated wood, becoming xedTey resist leaching. Because waterborne pre-servatives leave a dry, paintable surface, theycommonly used to treat wood for residential


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applications, such as decks and fences. Wa-terborne preservatives are used primarily totreat softwoods because they may not fullyprotect hardwoods from soft-rot attack. Mosthardwood species are difficult to treat withwaterborne preservatives. Tese preservativescan increase the risk of corrosion from treatedwood used in wet locations. Metal fasteners,connectors and ashing should be made fromhot-dipped galvanized steel, copper, siliconbronze or stainless steel if they are used withwood treated with waterborne preservativescontaining copper. Aluminum should not beused in direct contact with waterborne preser-vatives containing copper. Borates are anothertype of waterborne preservative; however, theydo not x in the wood and leach readily if theyare exposed to rain or wet soil. Borate treat-ment does not increase the corrosivity of thetreated wood to most metals.

Chromated Copper Arsenate (CCA)Wood treated with CCA (commonly

called green treated) dominated the treatedwood market from the late 1970s until 2004.CCA has decades of proven performance andis the reference preservative used to evaluatethe performance of other waterborne woodpreservatives during accelerated testing.Chromated copper arsenate has been phasedout voluntarily for most applications aroundresidential areas and where human contact isprevalent. Currently, the most common usesfor CCA are treatment of poles, piles andheavy timbers.

Ammoniacal Copper Zinc Arsenate(ACZA)

ACZA is a renement of an earlier for-mulation, ACA, which is no longer availablein the United States. Te color of the treatedwood varies from olive to bluish green. Tewood may have a slight ammonia odor until ithas dried thoroughly. ACZA is an establishedpreservative that is used to protect wood fromdecay and insect attack in a wide range of ex-posures and applications. Te ammonia in thetreating solution, in combination with process-ing techniques such as steaming and extendedpressure periods at elevated temperatures,allows ACZA do a better job of penetratingdifficult-to-treat species of wood than manyother water-based wood preservatives. ACZAis used frequently in the western United Statesto treat Douglas r lumber and timbers, polesand piles.

Alkaline Copper Quaternary (ACQ)Compounds

Alkaline copper quat (ACQ) preservativeshave become widely used in recent years asalternatives to CCA in residential applications.Several variations of ACQ have been standard-ized. ACQ type B (ACQB) is an ammonia-cal copper formulation that is primarily used

in the western United States. ACQ type D(ACQD), the amine copper formulation, isthe most commonly used in most of the UnitedStates. Some manufactures are producing amicronized form of ACQ where very nelyground copper is suspended in water instead ofdissolved in the amine co-solvent.

Copper Azole (CAB)Copper azole is another recently developed

preservative formulation that relies primarilyon amine copper, but with additional biocide

(tebuconazole), to protect wood from decayand insect attack. Copper azole is an amineformulation. Ammonia may be added at thetreating plant when the copper azole is usedon species that are difficult to treat, such asDouglas-r.

Copper HDO (CX-A)Copper HDO is an amine copper water-

based preservative that has been used inEurope recently introduced into the UnitedStates. Te active ingredients are copper oxide,boric acid and copper-HDO (Bis-(N-cyclo-hexyldiazeniumdioxy copper). Te appearanceand handling characteristics of wood treatedwith copper HDO are similar to the otheramine copper-based treatments. It is also re-ferred to as copper xyligen. It is currently onlystandardized for aboveground applications.

Propiconazole-Tebuconazole-Imidacloprid (PTI)

P I is a recently standardized preservativethat does not contain copper. Te propicon-azole and tebuconazole are fungicides, whilethe imidacloprid helps to protect against in-sect attack. P I does not add any color to thewood. P I-treated wood is currently standard-ized only for aboveground applications.

BoratesBorate compounds are the most com-

monly used unxed waterborne preservatives.Unxed preservatives can leach from treatedwood. Tey are used for pressure treatment offraming lumber used in areas with high termite


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hazard and as surface treatments for a widerange of wood products, such as cabin logsand the interiors of wood structures. Tey arealso applied as internal treatments using rodsor pastes. At higher rates of retention, boratesalso are used as re-retardant treatments forwood. While boron has many potential appli-cations in framing, it is not suitable for manyapplications because the chemical will leachfrom the wood under wet conditions. Boratepreservatives are available in several forms,but the most common is disodium octaboratetetrahydrate (DO ). DO has higher watersolubility than many other forms of borate,allowing more concentrated solutions to beused and increasing the mobility of the boratethrough the wood. With the use of heated solu-tions, extended pressure periods and diffusionperiods after treatment, DO can penetratespecies that are relatively difficult to treat, such

as spruce.Treatments for Wood Composites

Many structural composite wood products,such as glue-laminated beams, plywood, paral-lel strand lumber and laminated veneer lumberare typically pressure treated with wood preser-vatives in a manner similar to lumber. However,ake- or ber-based composites are often pro-tected by adding preservative to the wood fur-nish during manufacture. Te most commonlyused preservative for these types of composites

is zinc borate. Zinc borate is a white, odorlesspowder with low water solubility that is addeddirectly to the furnish or wax during panelmanufacture. Zinc borate has greater leach re-sistance than the more soluble forms of borateused for pressure treatment and thus can beused to treat composite siding products that areexposed outdoors but partially protected fromthe weather. Another preservative that is usedto protect composites is ammoniacal copperacetate, which is applied by spraying the preser-vative onto the OSB akes before drying.

Precautions with PreservativeTreatments

Creosote, pentachlorophenol chromatedcopper arsenate (CCA) and ammonical copperarsenate (ACZA) are all classied as restricteduse pesticides by the U.S. Environmental Pro-tection Agency. Tese preservatives shouldonly be used where used where protection frominsect attack and decay is important because ofhazardous conditions caused by moisture, lackof wood resistance, high temperature and expo-

sure to destructive organisms. Use or exposuto wood treated with preservatives may prescertain hazards, so take these precautions whhandling the treated wood and in determininwhere to use or dispose of the treated wood.

Use-site PrecautionsAll sawdust and construction debris

should be cleaned up and disposed of after cstruction. Do not use treated wood under cir-cumstances where the preservative may becoa component of food or animal feed. Exampof such sites would be use of mulch from re-cycled arsenic-treated wood, cutting boards,counter tops, animal bedding and structuresor containers for storing animal feed or humfood. Only treated wood that is visibly cleanand free of surface residue should be used fopatios, decks and walkways. Do not use treawood for construction of those portions of bhives which may come into contact with honreated wood should not be used where it macome into direct or indirect contact with drining water except for uses involving incidentcontact such as docks and bridges

Logs treated with pentachlorophenolshould not be used for log homes. Wood treaed with creosote or pentachlorophenol shoulnot be used where it will be in frequent orprolonged contact with bare skin (for exampchairs and other outdoor furniture), unless aneffective sealer has been applied. Creosote- pentachlorophenol-treated wood should not used in residential, industrial or commercialteriors except for laminated beams or buildincomponents that are in ground contact and asubject to decay or insect infestation and whtwo coats of an appropriate sealer are applieDo not use creosote- or pentachlorophenol-treated wood for farrowing or brooding facilties. Wood treated with pentachlorophenol ocreosote should not be used in the interiorsof farm buildings where there may be directcontact with domestic animals or livestock tmay crib (bite) or lick the wood. In interiorsof farm buildings where domestic animals olivestock are unlikely to crib (bite) or lick thwood, creosote or pentachlorophenol-treatedwood may be used for building componentswhich are in ground contact and are subject decay or insect infestation and where two coof an appropriate sealer are applied. Sealersmay be applied at the installation site. Ure-thane, shellac, latex epoxy enamel and varniare acceptable sealers for pentachlorophenol

treated wood. Coal-tar pitch and coal-tar pitc


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emulsion are effective sealers for creosote-treated wood-block ooring. Urethane, epoxyand shellac are acceptable sealers for all creo-sote-treated wood.

Handling PrecautionsDispose of treated wood by ordinary trash

collection or burial. reated wood should notbe burned in open res or in stoves, replacesor residential boilers because toxic chemicalsmay be produced as part of the smoke and ash-es. reated wood from commercial or indus-trial sites (construction sites) may be burnedonly in commercial incinerators, according tostate and federal regulations.

It is legal to send treated wood to a land-ll, and the growing shortage of landll spaceis prompting many industrial users to selectrecycling of treated wood as their disposal op-tion.

Avoid frequent or prolonged inhalation ofsawdust from treated wood. When sawing andmachining, wear goggles to protect eyes fromying particles. Always remember to wear adust mask when sawing or machining wood toprevent inhalation of dust. After working withtreated wood and before eating, drinking or us-ing tobacco products, wash exposed body areas

thoroughly. If preservative or sawdust accu-mulates on clothes, launder the clothes beforereuse. Wash work clothes separately from otherhousehold clothing.

Selection of Pressure-treatedWood

In Louisiana, Southern yellow pine is the

most common preservative-treated wood. Teterm (SYP) lumber is a general term used togroup the following species together: loblollypine, shortleaf pine, longleaf pine and slashpine. A consumer needs to buy the appropriatequality of lumber that matches his or her end-use objective. Te most common grade of SYPtreated lumber found at building material deal-ers is Number 2 Common because it meets awide variety of use needs and offers a good val-ue. Te grade of a piece of lumber is based onthe number, character and location of growth

characteristics that may affect the strength orthe utility value of the lumber.o guide selection of the types of preserva-

tives and loadings appropriate to a specic enduse, the American Wood Protection Associa-tion (AWPA) developed Use Category System(UCS) standards. Te UCS standards simplifythe process of nding appropriate preserva-

Table 1. Typical use categories and retentions (pcf) for preservatives listed by the American WoodProtection Association and used in pressure-treatment of Southern pine species.

Preservative

Retegntions for Each Type of Exposure and AWPA Use Category DesignationInterior,Dry orDamp

Exterior Above-ground Soil or Fresh water Vertical,Coated Horizontal General

Severe/ Critical

Very Severe/ Critical

1, 2 3A 3B 4A 4B 4C 4C (Piles)Waterborne:

ACZA 0.25 0.25 0.25 0.40 0.60 0.60 0.80 ACQ-D 0.25 0.25 0.25 0.40 0.60 0.60 -CA-B 0.10 0.10 0.10 0.20 0.31 0.31 0.41CCA NLa NLa 0.25 0.40 0.60 0.60 0.80CX-A 0.21 0.21 0.21 - - - -

PTI 0.013 0.013 0.013/0.018 b - - - -DOT (SBX) 0.17/0.28c - - - - - -Oil-type:Creosote 8.0/NRd 8.0 8.0 10.0 10,0 12.0 12.0Pentachlorophenol 0.40/ NRd 0.40 0.40 0.50 0.50 0.50 0.60CuN (oilborne) 0.04/ NRd 0.04 0.04 0.06 0.075 0.075 0.10a NL: EPA labeling does not currently permit use of wood newly treated with these preservatives in most applications within theseUse Categories.b Higher retention specied if the preservative is used without a stabilizer in the treatment solutionc Higher retention for areas with Formosan subterranean termitesd NR: Not recommended for interior use in inhabited structures


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tives and preservative retentions for specic enduses. Tey categorize treated-wood applicationsby the severity of the deterioration hazard.Te lowest category, Use Category 1 (UC1) isfor wood that is used in interior constructionand kept dry, while UC2 is for interior woodcompletely protected from the weather but oc-casionally damp. UC3 is for exterior wood usedaboveground, while UC4 is for wood used inground-contact in exterior applications. UC5includes applications that place treated wood incontact with seawater and marine borers.

o use the UCS standards, one needs onlyto know the intended end-use of the treatedwood. A table in the UCS standards lists mosttypes of applications for treated wood, andgives the reader the appropriate use categoryand commodity specication. Te commod-ity specication lists all the preservatives thatare standardized for that use category, as well

as the appropriate preservative retention andpenetration requirements. Te user needs onlyspecify that the product be treated accordingto the appropriate use category. Te use cat-egories and preservative retentions for some ofthe most common preservative treatments areshown in able 1.

As the treating industry adapts to the useof new wood preservatives, it is more importantthan ever to ensure that wood is being treatedto standard specications. In the United States,

the U.S. Department of Commerce, AmericanLumber Standard Committee (ALSC) accred-its third-party inspection agencies for treatedwood products. Quality control overview byALSC-accredited agencies is preferable to sim-ple treating-plant certicates or other claims ofconformance made by the producer without in-spection by an independent agency. Wood that

is treated inaccordancewith thesequality as-

surance pro-grams willhave a qual-ity mark orstamp of anaccreditedinspectionagency onthe wood oron the end-

tag (Figure 22). Te use of treated wood withsuch third-party certication may be mandatby applicable building code regulations. In adition to identifying information about theproducer, the stamp indicates the type of preservative, the retention level of the preservatand the intended exposure conditions. Retention levels are specic to the type of preservtive, species and intended exposure conditio

Self-applied TreatmentsTe consumer of untreated lumber can ap

ply preservatives in a do-it-yourself manner temporary conditions. Preservatives may be plied to wood in the eld by brush, spray, soor dip treatments. Te spray or brush methodis by far the most common for the homeownor hobbyist. Its important to realize that eltreatments give much poorer penetration orretention than factory-treated lumber. Mostexterior wood treatments penetrate only thewood surface and leave the inner core of wounprotected. Also, the risk of toxic exposurethe individual and the environment is increawith eld treatments. It is recommended thatpreservatives applied in this manner be accopanied by the application of a water repellanafter drying. A water repellant used withouta ground-contact-approved preservative willgive unsatisfactory decay resistance when uin ground-contact situations. Because woodabsorbs moisture approximately 20 times eaalong the grain than across the grain, the ap-plication of a water repellent is critical at theend-grain region. Some self-application woopreservatives have a water-repellent compo-nent. See your local retail store for assistancA water-repellent preservative differs from awater repellant in that the former contains amildewcide, which provides for surface mildresistance.

Te performance of any paint depends onthe condition of the wood at the time of paining, the nature of the paint itself, the application conditions and the moisture movementthrough the painted surface once in service. ways follow the recommendations of the paimanufacturer. Once a satisfactory paint coatiis obtained, paint on treated wood surfaces woften outlast that on an untreated surface be-cause incipient decay and mildew beneath thpaint lm are a signicant cause of prematurpaint failure.

Figure 22 . Grade mark stamp of preservative-treated wood. (1) The

identifying symbol, logo or name of theaccredited agency. (2) The applicable

American Wood Preservers Association(AWPA) commodity standard. (3) The

year of treatment if required by AWPAstandard. (4) The preservative used,which may be abbreviated. (5) The

preservative retention. (6) The exposurecategory (Above ground, Ground

contact, etc.). (7) The plant name andlocation, or plant name and number,

or plant number. (8) If applicable,moisture content after treatment. (9) If

applicable, length and class.(Source: Forest Products Society)

Above Ground

NoName Wood 8

Preserving CompanyAnytown, AnyState

AWPA 6

UC3B0.25 7

pcf

2008 1 2009TradeName TM 2

For Above Ground Use 3 Alkaline Copper 4

XYZAgency

5

Above Ground

NoName Wood 8

Preserving CompanyAnytown, AnyState

AWPA 6

UC3B0.25 7

pcf

2008 1 2009TradeName TM 2

For Above Ground Use 3 Alkaline Copper 4

XYZAgency

XYZAgency

5

1 Year(s) of treatment2 Trade name of preservative treatment3 Intended end-use4 Standard name of preservative5 Third party inspection agency6 AWPA Use Category7 Retention of Preservative in wood8 Treating company


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Over-the-counter PreservativesTe requirements for an ideal wood pre-

servative include: (1) toxic to a wide range ofwood-inhabiting or destroying fungi, (2) highdegree of permanence (minimal leaching), (3)easy wood penetration, (4) noncorrosive tometals and nondestructive to the wood itself,(5) safe to use and handle and (6) economi-

cal. Te following list contains information onsome of the over-the-counter preservatives.Copper naphthenate will turn wood green

initially, but the color will often change tobrown after several months of exposure. Tishas traditionally been an oil-based formula-tion, but water-based solutions are now avail-able. Brush-applied treatments need a coppercontent of 1-2 percent or 10-20 percent coppernaphthenate. Its strong odor can be unpleasantto some people, and it should not be used inenclosed places.

Zinc naphthenate is a clear alternative tocopper naphthenate, but it is less effective inpreventing decay and mildew and should notbe used in ground contact. It is available in wa-terborne and solventborne formulations.

3-Iodo-2-propynyl butyl carbanate(IPBC) is commonly used as an ingredient inanti-sapstain formulations or as a fungicide inwater-repellent nishes for decks or siding. Italso is used to treat millwork and may be com-bined with azoles to enhance efficacy againstmold fungi. It may be used as either a solventor water-based formulation. IPBC is colorless,and depending on the solvent and formula-tion, the treated wood may be paintable. Someformulations may have noticeable odor, butformulations with little or no odor are alsopossible. IPBC is not an effective insecticideand should only be used for above-ground ap-plications.

Copper-8-quinolinolate solutions aregreen-brown, odorless and toxic to many

wood-destroying organisms. It is not recom-mended for use in high degradation areas.It is permitted by the U.S. Food and DrugAdministration to be in contact with food andbeehives because of its low toxicity to humansand animals.

Borate preservatives or borates are amongthe newest preservatives available. Tey arederived from sodium borate, which is the samematerial used in laundry additives. Tey are

effective against decay, termites, beetles andcarpenter ants when used in above-ground ap-plications protected from wetting. Tese pre-servatives are odorless, do not corrode ferrousmetal fasteners and can be painted or nished.Tey can be sprayed, brushed or injected andare also available as boron rods that can beplaced into holes drilled into the wood. Teyremain stable as long as they arent exposed tostanding water or do not come into prolongedwet ground contact without a water-repellentseal coating.

Installation and Inspection TipsAs stated, the appropriate selection and

handling of lumber are critical forlong-term service. Proper installa-tion of preservative-treated woodwill help extend the usable servicelife of the structure. Te most

problematic areas with decks andhouses are areas where wood canremain wet or can trap water, suchas the area between the deck andthe house, joints and areas continu-ously exposed to precipitation. Ondecks close to the ground withoutsufficient clearance for inspection,remove a few decking boards every two to threeyears to inspect the supporting structure. In-spect all other outdoor wood structures yearly.

Proper installation will help prevent nu-merous moisture problems. Outdoor treatedlumber should have a small gap of 1/8 inch to1/4 inch between adjacent boards for properair circulation and movement. Also, dontinstall the end-grain of untreated lumber incontact with another piece of lumber or placeit directly on concrete. Water will wick into theend-grain. Te adjacent board or concrete willprevent the end-grain from drying (Figure 23).More moisture is absorbed throughthe end-grain of lumber than anyother location. If you observe thissituation on your house or deck,monitor it closely for decay. Moistureabsorption can be slowed by coatingthe end-grain of the lumber with asealer such as wax. Some manufac-tured lumber is sold already end-coated with a bright color.

Outdoor posts can be checkedfor decay by using a probe such as aknife, ice pick or screwdriver (Figure 24). If the

Figure 23. This poor method ofassembly will allow water towick into the end-grain of thistreated post near the ground. Stainhas already developed near theground contact region as a result ofexcessive water absorption. (Source:Forest Products Society)

Figure 24. Inspection of posts is simplyaccomplished with a probe. (Source:Forest Products Society)


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Figure 27. Decay on a wood deckshowing (A) mildew and (B)advanced decay. (Source: Forest

Products Society)

ConclusionsTe causes and control of wood decay,

degradation and stain are numerous. Manyproblems can be eliminated or greatly reducedby using the right wood for the right job. Lum-ber used outdoors should always be pressure-treated to the appropriate retention levelnecessary for the job. Also, water-repellent pre-

servatives applied yearly will slow weatheringof privacy fences, decks and outdoor furniture.Many problems with untreated wood could beeliminated by simply keeping it dry. Contactyour parish office of the LSU AgCenter forfurther assistance on wood decay, degradationand stain.

A

B


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ReferencesCassens, D.L., W.C. Feist, B.R.

Johnson, and R.D. De Groot. 1995.Selection and use of preservative-treated wood. Forest Products Soci-ety. Madison, Wisc. 104 p.

Forest Products Laboratory.1999. Wood handbook: Wood as anengineering material. U.S. Dept. ofAgric. For. Serv. Agric. Handb. No.72. Washington, D.C. 466 p.

Freeman, M.H., .F. Shupe, R.P.Vlosky, and H.M. Barnes. 2003. Past,present, and future of preservative-treated wood Forest Products Journal53(10):8-15

Haygreen, J.G. and J.L. Bowyer.1989. Forest products and wood sci-ence. 2nd ed. Iowa State Univ. Press.Ames, Iowa. 500 p.

Hunt, G.M. and G.A. Garratt.1967. Wood preservation. 3rd ed.McGraw-Hill Book Co. New York.433 p.

Kirk, .K. 1973. Te chemis-try and biochemistry of decay. p.149-181. In: D.D. Nicholas (Ed.)Wood deterioration and its preven-tion by preservative treatments. Syra-cuse Univ. Press. Syracuse, N.Y. 380p.

Knight, F.B. and H.J. Heikkenen.1980. Principles of forest entomology.

5th ed. McGraw-Hill Book Co. NewYork. 461 p.

Koch, P. 1985. Utilization ofhardwoods growing on southern pinesites. Vol. 1. U.S. Dept. Agric. For.Serv. Agric. Handb. No. 605. U.S.Govt. Printing Off. Washington, D.C.1418 p.

Lebow, S. . 2004. Alternatives tochromated copper arsenate for resi-dential construction. Res. Pap. FPL-RP-618. Madison, WI: U.S. Depart-ment of Agriculture, Forest Service,Forest Products Laboratory. 9p.

McDonald, K.A., R.H. Falk, R.S.Williams, and J.E. Winandy. 1996.Wood decks: Materials, construction,and nishing. Forest Products Soci-ety. Madison, Wisc. 93 p.

Moore, H.B. 1979. Wood-inhabiting insects in houses: Teiridentication, biology, prevention andcontrol. U.S. Dept. of Housing andUrban Devel. (HUD). Washington,D.C. 133 p.

Zabel, R.A. and J.J. Morrell.1992. Wood microbiology: Decayand its prevention. Academic PressInc. San Diego. 476 p.

U.S. Department of AgricultureRural Electrication Administra-tion (REA). 1973. Pole performancestudy staff report.


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Visit our Web site: www.lsuagcenter.com

Authorsodd Shupe, Ph.D., Louisiana Forest Products Development Center

Stan Lebow, Ph.D. USDA Forest Products LaboratoryDennis Ring, Ph.D., Department of Entomology

Louisiana State University Agricultural Center, William B. Richardson, ChancellorLouisiana Cooperative Extension Service, Paul Coreil, Vice Chancellor and Director

Louisiana Agricultural Experiment Station, David Boethel, Vice Chancellor and Director

Pub.2703 (5 M) Rev. 6/08

Issued in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June30, 1914, in cooperation with the United States Department of Agriculture. Te LouisianaCooperative Extension Service provides equal opportunities in programs and employment.

Causes and Control of Wood Decay

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