Building material - Timber

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Sawing of timber.

Transcript of Building material - Timber

AR102 Building Materials and Construction 1.

TimberProducts of wood suitable for construction purpose Trees to suit timber should be felled immediately after maturity. Classification of Trees Endogenous growing by addition of tissues inwards palms, bamboos etc. Exogenous growing by addition of new tissues outwards other common trees. Exogenous further divided into: Softwood conifers like pines and spruces with needle like leaves. Also show distinct annual rings. Hardwood - mostly broad leafed trees , deciduous trees, shedding leaves annually.

Timber.Structure of Wood Outer bark Inner bark - bast Sapwood Immediately underneath the inner bark New layer of tissues forming outwards from top to bottom Growth rings

Outer layers Sapwood moist & living and inner layers Heart wood dead and strong partGroups or bundles of cells growing in horizontal direction Medullary rays Centre of the trunk Pith or Medulla

Timber.Conversion & Seasoning of Timber Process of cutting & sawing logs into suitable sections of timber Conversion Drying timber in controlled condition to remove all the sap and to reduce moisture content without splits & distortion of wood - Seasoning

Timber.Conversion of Timber.. Ordinary sawing wood is simply sawed normal to its diameter. Most economical method. As each plant will have outer portion of sapwood and inner portion of heartwood there will be differential shrinkage & warping. Quarter sawing suitable when there is no medullary rays. Tangential sawing flat grained sawing produces planks which warp too much. Radial or rift sawing generally used method for hardwoods. This timber doesnt shrink too much. Decorative finish due to interplay of grains. But wastage is maximum.

Ref: http://westcoastlands.net/SawmillCuttingMethods.html

Timber.Seasoning of Timber Natural or Air seasoning Carried out by stacking sawn timber horizontally in layers in a covered shed, separated by wooden battens. May take 2-6 months. Artificial seasoning Kiln drying timber placed in an airtight chamber, air at 35-38 degree C is circulated. Humidity is reduced slowly and temperature increased till the desirable moisture is achieved. Boiling sawn timber boiled for 3-4 hours, in order to remove sap. Chemical seasoning by immersing in salt water. Electrical seasoning by passing high frequency alternating current. Water seasoning sawn timber are immersed in running stream with thicker end of original log facing upstream. After 2-4 weeks when sap has been washed out, timber is air dried.

Timber.Market forms of timber Battens Planks Boards Baulks Deals Scantlings Quarterings 50-100mm thick and 125-200mm wide thickness50mm thickness100mm cross section exceeding 50x50mm softwood 50-100mm thick and width >250mm 50-100mm thick and 50-100mm wide joists square pieces 50x50mm-150x150mm

Timber.Defects in Timber

Knots Sections of the branches of the tree present on the surface of wood. They can be nail knots (40mm dia) Also they can be tight knots or loose knots.

Shakes Cracks and splits in the log due to many reasons like excessive heat, frost or twisting due to wind during the growth of a tree. Types cup shake, heart shake, ring shake, star shake etc.

Timber.Defects in Timber.. Twisted grain/fibre defect in the tree may be caused by wind. Upset or Rupture of fibers due to strong winds, bad felling etc. Wane presence of actual rounded surface of the tree remaining in timber. Presence of Sapwood less durable than heartwood and should not be used in important places. Sloping grains when timber is sawn parallel to the pith. Cracks, fissures, resin pockets -

Wane

resin pockets

Timber. Treatment of TimberTreatment with preservatives before used in timber work and regular maintenance afterwards like painting. Preservative treatments Charring surface is burnt and burnt surface act as a protective coat. Painting with tar or creosote fence post re preserved in this method. Treatment with preservatives ASCU is an important preservative used in Indiacompound of Arsenic, Copper Sulphate and Potassium Chromate. Brush & spray paint Immersion Hot & Cold open tank treatment Pressure & Vaccum treatment Treatment by Diffusion for green timber, very soluble Boron compounds are applied on the surface and over a period of one month or more, the compound diffuses into the wet timber and acts as a preservative. Further reading: http://lecture.civilengineeringx.com/c/traditional-materials/

Timber. Causes of DecayFungal Decay (dry rot & wet rot) dry rot happens in moist conditions and wet rot in very damp conditions. Remedy is drying out the material, removing the affected part and applying fungicide to prevent further infection. Attack by beetles and borers- insects lay eggs in crevices in the wood which hatch to larvae and feed on the timber. Remedy is to treat wood with insecticide and preservatives. Termite attack softwood is more prone than hardwood. Remedy is time to time inspection and treatment with specific anti termite chemicals.

Timber. Common timberTeak - Tectona grandis Moderately hard, teak is durable and fire-resistant. It can be easily seasoned and worked. It takes up a good polish and is not attacked by white ants and dry rot.

Mahogany Swietenia spp It takes a good polish and is easily worked. It is durable under water. It is most commonly used for furniture, pattern making and cabinet work.Ref: http://en.wikipedia.org/wiki/List_of_Indian_timber_trees

Timber.Common timber. Aajili/Aini Artocarpus hirsutus durable timber which is comparable in quality with teak. It is termite and fungus resistant and survives well even in brackish water. Rosewood / Eeti Dalbergia Latifolia - It is strong, tough and close-grained. It is a handsome wood that takes up a high polish. It maintains its shape well and is available in large sizes. It is used for furniture of superior quality, cabinet work, ornamental carvings and so forth. Ref: http://keralaflora.blogspot.in/search/label/trees%20of%20kerala

Timber.Common timber.

Ref: http://ecoport.org/ep?SearchType=earticleView&earticleId=127&page=1423