CHAPTER EIGHT

MASONRY MATEruALS,

TOOLS, aruLMETFIODS

ou may lr'onder lr''hy I rvould spend

a chapter discussing materials, since

I am also going to give you a set ofplans and a list of materials to buy. I am do-

ing it because some people just rvon't fbllolv

directions! Ard if you are one of them, and

want to modifv, customize, or interpret as

you go, a question about materials mav come

up in your planning or construction process

that cannot be ansrvered bv the people at the

building supplv. masonrv suppl1., or even the

refiactory supply store. I hope you will be

able to answer it here.

Masonry Materinls

Brick. stone, concrete, and sand are masonry

materials. Although masonry materials are

strong, most of them are brittle. They are

stronger in compression than in tension (that

is, pushed together as opposed to pulled

apart), and will lail if exposed to vibration

or shearing forces. Though resistant to

heat, thev u'ill thil if rapidly cooled. Metal

reinforcement must be used cautiousll, in

heated masonry, as it expands and contracts

differently.

CEMENT, CONCRETE, AND MORIAR

The essential material for most masonry con-

struction is cement. This bonds the other ma-

terials together. When sand and small stones

are bound together, the product created is

called concrete. Common mortar is sand ina cement (rvithout small stones) ll'ith lime

added to increase adhesion ar-rd flexibility. Itis placed betrveen bricks, blocks, or stones to

bind and bed them.

Pou'dered cla-v ma1. be added to make the

mortar easier to work, but it decreases the

mechanical strength of the mixture, u'ithoutincreasing its heat resistance unless the mortar

is primarilv clay, rvith little cement present.

At that point the mortar is weak, but heat-

resistant. For concrete, heat resistance is de-

pendent on the qpe of cement and the tvpe

llHrfh!fl

,l

i;

t57

of aggregate (filler) used. \A/hen the cement

is resistant to high temperatures, it is called

refractory cement; mixed with an appropri-ate aggregate, it becomes refractory concrete

or mortar. When cement cures by taking upwater, sets under water, and is resistant towater when set, it is called a hydraulic ce-

ment. Most other types of cement are airdrying, although some refractory mortarsare heat-setting.

Straight cements don't have a great deal

of strength when bridging large gaps; theyrequire a filler material, or aggregate, to cor-

rect this potential weakness. The aggregatebridges the gaps and provides many of thequalities of the finished product. These couldinclude compressive strength, a low coef-ficient of thermal expansion, uniform grain

size, light weight, or high thermal insulationperformance. Choosing an aggregate requiresbalancing physical properties desired againstthe cost and local availability ofthe aggregate.Common aggregates are mined in their finalform (sand, gravel) or are produced by a

simple mechanical process (crushed stone).

Specialized aggregates are manufactured fromraw materials by subjecting them to heat (as

is the case with perlite, expanded shale, ancl

vermiculite).

PORTI-AND CEMENT

The most common type of cement is Port-land cement, so-called because of the re-

semblance it bears to a type of limestoncquarried near Portland, England. It is pro-duced by burning clay or shale and hieh-calcium minerals to produce cinders that rrrc

then ground very fine to make a wettabt.powder. The hardening of Portland cemen:and the concrete and mortars made from ::

occurs as the result ofhvdration: the ceme::takes on water.

For general masonrywork, the advantagc.

ofPordand cement include its high streng-relatively low cost, widespread availabili:and versatility. It can be used in concre::and a variety of mortars when modifiec r,

other ingredients. Its limitations in o\ i:building are its slow acquisition of srrenc-:as it sets, the loss of strength developm;::

Concrete gets its strength frowits agregate. Sharp aggregatethat is yaried in size mahes

stronger concrete.

round aggregate

small aggregate added

sharp aggregate

158 THE BREAD BUILDERS

1

i

ir rhc cor L( I)rtroicrrnsu'cngd

:35 &.iagrcaad nolcrr 62?yttna I$€rnodi-[r,jc€:irE nfr rram-( sfii{omsr rs h,afnilff bty

frcm vqts?ltctrerrn brd

"t{"{sO}nI{anmm,frodhrye&

ffimmmmm h*n*,rlhg, qp{m o[L!!E!

T*{-K rffr&r pruedo$rotddfu.r-"fficrryrh *m rfe

trrh 1r4tEl|ffiFrhtrr.lr*.un@rrsriii --'l- *kbmipb-

if the cement is mixed with too much s'ateror is prematurelv dried, and its relativeh'lou'tolerance for heat. Cured, Portland has ftillstrength up to about 450 degrees Fahrenheitr235 degrees Celsius), half strength at 750clegrees Fahrenheit (400 degrees Celsius),and no strength at 1,150 degrees Fahren-heit (625 degrees Celsius). Strength tl.oes nott'(turn vhen it cools. Even at temperatures inthe moderate range (700 degrees Fahrenheit,370 degrees Celsius), repeated c,vcles ofheatare not u'ell tolerated. Portland cement con-

tains silica compounds and breathing cementdust is best avoided. Also, Portland and allother hydraulic cements will suck moisturetiom your skin, even rvhen the cement is ina \\'atery phase. This may lead to chapped orer-en broken skin.

.\L{SONRY CEMENT

Masonrv cement is a Pordand cement modi-fied b,v adding lime. This allou's mortars madefiom it to grip more rightlv to brick, stone,or block, and it makes the working (tror,vel-

ling) qualitie s of the mortar better. There is

no incrcase in hcat resistance.

SACI(MIX

This product comes premixed and bagged,and is sold at hardlvare stores, lumber1.nrd5,

and bv masonrv suppliers. It is available as

either mortar or concrete mix. All vou add

is n'ater (directions on the bag say hor,v

much) and elborv grease ro mix up small

quantities. Sack mixes are more expensive

than home-blended cement products, butvolr may save enough in aggravation (mov-ing sand, dealing rvith half-used bags ofcement) to make them u'orthwhile on an

oven job.

Sack-mix mortar is useful for laying blockin the ash pit rvalls, and sack-mix concrete

r.nar-be used for the foundation slab. It may

also be used as the cladding of a householdoven. When determining horv many bags topurchase, read the label carefully: it takes a

lot of bags to pour a slab. Also, be sure voudon't or.,erload your pickup truck and vourback-arrange a delivery if vou can.

The major concern about sack-mixconcrete is the aggregate. Often these are

rounded gravel and quartz sand. This lear,es

the concrete u.ith fairly low tensile strengthas r.vell as relatively poor heat tolerance. Sack

mixes are fine for a slab on grade, adequate

for the cladding or the hearth slab of a home

oven, but are best avoided for cladding orhearth slabs of ovens larger than 32 x 36

inches, or ovens used ever1, da1,-..t".0,.rtof size. Refractorv concretes are better inthese applications.

TRANSIT MIX

Transit-mixed concrete is the kind that is de-

livered in big trucks, coming from a central

plant. It is great stufl, but the minimum or-

ders are too big fbr rnost oven u.ork, even forslabs. Sometimes vou can pay an extra fee tohave a small order delivered, though.

CALCIUM ALUMINATE CEMENT

Calcium aluminate is a cement that is similarin use to Portland, but which avoids some

of its problems. It is made of bauxite (ore

that contains alumina) and limestone. Thiscement reaches good compression strengthin one dav (it is ah,vavs rveaker in tensionthan Portland). It is sold both for this early

strength quality and for its heat resistance.

It is the heart of refiactory concretes, and

:,

=.=F

FFF

MASONRY N,TATERIALS. TOOLS. .\\D I{ETHODS 159

*Retiactorv con-cretes tbr ovens

are covered in the

American Socieq'

fbr Testing and

Matcrials C 401

chssifications. u'hilerefracton' mortarsmust lnect AsrNt (l

199, Medium-duwspecifications.

buying it in the tbrn'r ol calciurn aluminate

cement and making vour o\\'n refiactor)'

concrete is cheaper than buving proprietarv

brands of refracton' concrete.

The most extensive line of this cement

is from LaFarge Calcium Aluminates, Inc.,

*'ith an office in Virginia (f -800-524-

8463) that can refer to local distributors

or ship directly. Their least expensive ce-

ment is Fond.u, at 38 percent alumina. This

product is resistant to heat of at least 950

degrees Fahrenheit (5L0 degrees Celsius)

r,vhen made into concrete with quartz ag-

gregate, i,500 (825) u'ith traprock, 1,900

(1,150) r.vith vermiculite, 2,000 (f,200)with expanded clavs, and 2,400 (1,300)u'ith crushed firebrick. Progressivelv more

heat-rcsistant and e xpensive cements are

ar.ailable, u'ith higher alumina contents, but

for oven construction, all calcium aluminate

cements should have less than 45 percent

alumina, so that thev rentain rcsistant to

thermal cycling.

Of the aggregates mentioned, the most

common one used in heat-resistant oven

slabs and claddings is traprock, a u'idelyavailable crushed basalt. Using LaFarge

Secnr 4l (41 percent alumina cement) the

mix q'ould be:

. cement-94 pounds

. traprock, 3/+ x 3/s inch-230 por'rnds

o fine manufactured sand (traprock)-I88pounds

. \\.ater-not to exceed 41l: gallons

If getting all those materials is not pos-

sible, consider a premixed alumina concrete

like LaFarge's Fond.ag, ilit is cheaper in 1'ourlocation than a proprietar-v castable reflactort'

of the same strength and heat resistance.

Calcium aluminate cement costs three tofir'e times as much as Portland cement and

is much harder to find, but in appropriate

applications it rvill not add as much in cost

as it u'ill add in longeviw and convenience.

A rvord of caution: e\ren a little of this prod-uct in uncured or dust form may drastically

accelerate the setting of Portland cement

products, creating so-called flash setting.

Don't mix them.*

FIRECLAY

Fireclav is a heat-resistant clav that is avail-

able in a dr-v por,vder fbrm to use as an ad-

ditive to mortars. It imparts little of the

refractorv qualitie s of firebrick to mortars

made lvith non-reliact<)rv cernents. Its chie fbenefit is the plasticitv it gir.es to mortars,

allorving them to be smoothl,v butteredinto place. It reduces the tensile strength ofconve ntional mortar si gnifi cantl,r.', but this

is not much of a concern because mortars

are not relied on fbr strength except incompression. Thick (mortar consistencvr

suspensions of fireclay u'ith a little fine

crushed firebrick or pottery grog (crushe.1

ce ramic) and a small amount of Portlan,,l

cement (to thicken them) can be used to se tbrick used fbr dome and arch constructions

that are exposed to high heat anci compre s-

sive fbrces. foint lines in that case shoul.-l

be narron, (approximateh' t/r inch).Naturallv occurring fireclav is the basic

ingredient in common firebricks; its resis-

tance to heat and its dimensional stabilitrcome from its relative lack olminerals thlis'ould serve as flux for its f'urther fusion

Its he at re sistance increases rvith its alumin "content.

'l.

I60 THE BREAD BUILDERS

nruch iibout the uses and technical specifica-RIFIL{CTORY CIMENTS tior.rs of the products, and the product names

There are man\r t\pes of commerci,rl rcfi,rc- rre otten not helpful. Ask for the name oftorv cements, ntortars, and concrete, knou'tt .r1 clqinccrillg representative lyho can helpb1,aconfusirlgrangeclftradenamesbut,rs- r'ou (in person or by phone) and get thesigned to groups b,v their properties ancl mirnuflcttirer'scatalogsanddatasheetsontheuses. Drv-sl-ripped castable refractorie s are prcducts \.ou plan to use. Anv castable u.hichthe largest group, sold to be mixed r'vith rva- is exposed to thermal cvcling should have anter, then pourcd, pumped,tror'velled, or shot from a

gun. Refiactories mav be ei-

ther hvdrauiic or air-dn ing.With each q,'pre of installa-

tiort a r.rngc of propertics is

available, such as densitv and

insulltion characteristics, irr-

cre ased resistance to thcrmalsl-rock, abrasion, shrinkage,

thermal expansion, ctc. Allol- them hlr c strict mi-r-

ing requirements (n()t toomuch u atcr, avoid olcrrnir-ing) that must be fbllou.edto preservc their thermal

o.cling endurance.

In general, castable refiac-

tories do not shrink or expand

rnarkedlv rvith air curing orshrink nruch aftcr fire curiug,although tl-rey do expandslightlr. u'hile hot. Refractorv

Buying refi,actory

ruaterials ca,n be

frwstrating becnuse

snlespeople usua.lly

d,on't know tuLach

about the uses

and. technicnl

specif,cations of the

prod.ucts, end the

prodwct nrr.nues &re

often not helpful.

Ask.for the nanoe ofnn engineering

repyesenta.tiye who

can belp yoa.

alun-rina content of 35 to 45

percent) and a porositl, of2Opercent or more , to reduce

cracking. Avoid using steel

rci rr Forcernen t i n refractories

exposed to higl-r heat (oven

heartl-rs or inne r domes). Putthe steel in an onrer claddingor slab that has srnaller tem-

perature cvcles.

HEAT-RESISTANT

MORTARS

These include fiactorl,-11x6[s

clarr-based mortars con-

sisting of fireclav and fine

sand, hornemade clav mor-tars made of reht'drateddn, clay mixed 3 to 5 parts

fine sand to one part cla._v,

and the sarne clal' frortarsr.vith 3 to 8 percent Port-land cement added to heip

mortars rnade u'ith rcfractorv cements and the mortar 51xy ((f11"-to resist slumping.

aggregates tend to re duce loosening of the FIeat-resistant ntortars also include r\\.o gen-bricks in oven u'alls and don-res because of eral types ol refractorl. ntortars, both u,iththeirgooddimensionalstabilinr Lightweight pulverized firebrick as aggregare. C)ne rvpecastables contain lighm'eight aggregate and is based on calcium aluminate cement (con-have thermal conductirdties that are one -fifth r-enient since it sets at room te mperature andto one-half of conventional castables. canbridgelargergaps)andtheotherisbased

Buving refractory materials can be frustrat- on rvaterglass, or sodium silicate, u.hich setsing because salespeople usuallv don't knou' at temperatures of about J.,000 degrees F.

I,IAS () N RY N,IAT t RIALS.'I O O L S. A.r-- D M ETH O l) S t6t

All heat-resistant mortars are applied in nar-

rorv joints-never o\-er t/'l inch for calcium

aluminate mortars and never over r/s inch forfireclav or rvaterglass mortars.

FIREBRICK

Firebrick is the solid equivalent of castable

refractories. It is available in full densitv orlighnveight (insulating) makeup in several

51,pes and grades. For ovens, it is fine to use

standard lorv- durv "fireclav fi rebrick, " r'vhich

costs $ 1.00 to $ 1.50 a brick. This is manufac-

tured by adding firecla1, to ground firebrick(grout), sand, alumina, and silicate rock and

is good to about 2,700 degrees Fahrenheit(1,500 degrees Celsius), r,vhich is far above

the temperatures vou lvill ever achieve in \rouroven. Higher-percentage alumina firebricksare more resistant to heat and abrasion (good

for pizza hearths), but they have a disad-

vantage in bread ovens: the higher-aluminabrick is more conductive, and mav transfer

an excessive amount of heat to the bottomof the loaf. AIso, high-duw firebricks are

actuallv less resistant to cycles of heating andcooling such as those experienced by oven

brickr,vork, and are rnorehkely to crack, spall,

and fail than standard firebrick: lorv-duryfirebrick contains tin,v voids into r.vhich the

solid material of the brick can expand 'nvhen

it is heated.One modern design for a French

h-vbrid-sq4e bread oven specifies a firebrickhearth of 25 to 28 percent alumina. Thisis approximately the percentage in standard

firebrick, u'ith a conductivitv about 75 per-

cent that of medium-dutv firebrick and 60

percent that of super-dut,v firebrick. In Fin-land, France, and other European countries,special materials are maufbctured for oven

hearths that are even less resistant to heat

than standard firebrick, but more resistant tothermal shock. If thev lvear out mechanicalh.,

thev are simply replaced. If you are expe-

riencing premature mechanical r,r'ear in thehearth ofa bread oven because ofgas firingor excessive mopping, n-redium-dutv brick is

probablv the most heat-resistant brick voushould consider.*

RED BzuCK

Brick or red brick is made gy pulr.erizingclav or shale (u'hich geologically is basicallv

old and compressed clay), ther-r compressingit into a block, drving it, and firing it untilit is fused (vitrified) bv the action of mineralfluxes preserrt in tl-re clav The vitrificatior.rtemperature is reached in six to eight hours.Faster heating might cause rhe green brickto explode. The temperature reached in fir-ing in part determines the hardness and po-rositv of the brick. The density of the brickderives from its collstituent materials andthe lbrce with u'hich they are pressed to-gether. Uniform, high-quality red brick iseasily available for use in ovens. Some Bpesof irregular bricks or used bricks may be

more attractive lbr oven fronts or exterioroven r.valls u,here aestheticallv appropriate.Brick is available in a varietv of shapes, in-cluding a bull-nose brick that makes an at-

tractive lip on the front end of the hearthof a masonry oven. The rounded end is also

resistant to chipping.Not all red bricks offer the same mechan-

ical qualities, and nor all have been fired tcr

the same temperature. Some masons belier-e

that high-fired bricks are berter for expo-

slrre to heat because thev are thoroughlvvitrified and r,vill not further change shape

or size . Others are adamanr that high-fire d

*Standard

firebrickcorresponds

to -lsru c 27or cl26l.

-:.:-:-:

-!

t62 THE BREAD BUILDERS

bricks are too brittle for use insicle .rn ove n. structure. sancl could pop out of these bricks

=!F

--F

bricks are too brittle for use inside an ot'en,

ind recomlnend lorv-fired bricks fbr such

Iocations on the grounds that they u'ill be

nore resistant to thermal shock, thoughlcss strong.

Most of these opinions grew out of com-

mon and practical phenomena, related torhe q'a), bricks rvere originall,v fired and to

:l're historical lack of specialized firebrick in

cokrr-rial America. When bricks lvere fired in

rig open-air stacks or primitive kilns, some

'.iould be fired more than others. The higher-

:l Lcd bricks \\'erc more re sistant to \\'ctcr

J.rn-rage and weathering, and \\''ere Lrsed on

rhe outside of a chimnel' for that purpose.

Tl're rest of the bricks \vere softer, and rvere

-rsecl in the fireplace itself, l'here resistance

:() \\'ater \vas not inportant. If exposed to

crcessive heat, those bricks could rer.itrif"v to

r higher temperature.

Graduall,v the rule that soft bricks rvere

-:scd ir-r fireplaces developed, br-rt according

:,-r Greg Borchelt, an engineering consultant

:' ,r the Brick Institute of Ame rica. there is

.:ttle or no functional advantage to using

. rti bricks there; an1,u,ell-made brick r'r.ill

-:Lr. In o\rens, relativel], light (and there-: 'rc soft) red bricks u'ere historically used

: ,r the hearth (and replaced frequentll,)- , prevent burning the bottom of the::cad-not because thev r'r'ere particularlv-:sistant to heat.

-\merican-made bricks are fired to 1,950

: I,900 degrees Fahrenheit (1,050 to 1,600

,r:Srees Celsius), but some lumbervards also

-:irv common red brick from Mexico that.:e lot--fired, contain a lot of quartz sand,

-:r!'l are quite porous. Because these bricks-.,rv not have been fired ber,'ond the tempera-

:,-:e et u.hich quartz undergoes a change in

structure, sand could pop out ofthese bricks

irt high temperature. Avoid these ir-rferior

bricks bv l'rur ing dontestic otres.

Finalh', the maximum heat resistance lbr

red bricks and common firebricks is about the

same. Red bricks have a greater rate of expan-

sion, horvever, and are rnore likelr, to spall or

flake u'hen unequally heated. This can occur

l,'hen a hot fire is built and the surface of the

brick is heated too quicklr', or rvhen a jet of$'ater is spra-ved on the bricks. If an oven is

gently managed, there is little advantage lbrIirebrick, except as I have mentioned.*

BLOCK

Concrete block is manutactured b,v using

Portland cement to bind an aggregate ofsand

and fine gravel, u'hich is fbrced into molds

that produce the various shapes of block re-

quired. Some block is made in a shape that

allou's it to run along in a lvall, but not toterminate a u'a1l or turn a corner. There are.

hole\.er, blocks fbr ending u'alls and turn-

ing corners. Most blocks I'rave holes that run

verticallv through thern, called cores. Blocks

are ar.ailable in a r.arietv of sizes fbr u'alls ofdiiferent thickrress. or to rct as spaccrs in rrvall as necessarY.

Blocks ma.v be made out of lighnveight

aggregate to make them easier to la-v and

to provide some insulation value. Extra

insulation can be obtained by frlling the

holes in the blocks u'ith lightr.r.'eight mineral

products. A block u'all is usuall,v reinforced

u,ith steel bars embedded in mortar or con-

crete and placed verticalh,, horizontalll', or

both. Although blocks are usuallv mortared

together, mortar does not prorride much ad-

hesion to the block, and unreinfbrced u'alls

don't tolerate lateral force s u'ell.

fOOLS. AND rllETHODS

"Facir-rgbricks used

for oven

enclosures

outdoorsshould meet

lsru c 62,grade SW, or,rsnr c 216.

NTASONRY T\IATERIALS, 163

BASALT

Basalt is a dense ancl hard volcanic rock,

crushed and sold as traprock and rnanufac-

tured traprock sand. It is good fbr heat resis-

tant, high thermal mass concrete u.hen mixed

u'ith calcium aluminate cements.

GRANITE

This is a strong, igneous rock containing 20

to 50 percent quartz) held l'ith other crys-

tailine minerals in a granular arrangement.

It is moderatel,v dense and moderatel,v heat-

stable.

OLI\'INE

Olivine is a rock lbund u'ith basalt, serpen-

tines, and soapstone in areas ofpast volcanic

activit,v. It is often used as an aggregate inrefractories and high-temperature concrete

because it has verl. little thermal expan-

sion and good resistance to heat. It is ver,v

dense-sometimes over 3.5 times the density

of l'ater. Oven temperatures do not usuallt.

require such specialized aggregates, but ol-ivine sand is used by some manufhcturers ofprecast refractory oven componer-rts and itcould be used to increase the mass of an1'

masonr\r laver. Because it is used in fbundr,v

operations, it is u.idelv available.

QUARTZ

The most common mineral on Eartl-r, qLrartz

is silicon dioxide, r.r'ith a de nsitv of 2.65 times

that of lvater. \4rhen heated to 1,600 degrees

Fahrenheit (870 degrees Celsius) it under-

goes a change in crvstal structure) with a l5percent change in volume. This temperature

may well be reached at the inner surface ofan oven) so quartz aggregates should be

avoided for high-temperature use unless, as

in higl-r-fired brick, an.v quartz present has

been prer.iouslv heated. Quartz is a compo-nent of granites and is a r,vater-carried deposit

ir-r man,v other rocks.

SERPENTINF,

Less dense and softer than olivine, this is oneof the minerals cor.nmonlv used in Europe inpast \rears for building or lining ovens and fbrmaking urns) \rases) and ervers. Nthough it iscloselv related to asbestos, there is no particu-lar health risk in non-fibrous serpentine.

SOAI'STONE

Soapstone is r,er\, dense and resistant to heat.

It is often used fbr the hearths of pizza or'-

ens, but it should be covered rvith firebrickin bread oven hearths, as it passes too muchheat to the botton-r of the bread. It can be

can,ed into beautiful dooru'a\rs and outerhearths.

STONE

Stone, as crushed rock is commonly called, isusuailv made by mecl-ranicallv crushing hardrocks. The resulting stones are screened tc-r

size, and have sharp edges that interlocku'hen used as aggregate. This makes con-

cretes made lrom stone stronger than sack-

mix concretes rnade fiom rounded gravel.

F{eat resistance depends on the tvpe ofrockused.

GRA\TL

Gravel is a natural prodr.rct of generalh'

rounded small stones that are sized accord-

ing to the size of wire screen thev rvill pass

through. Gravel is a common aggregate lbrconcrete, but tensile and shear strength is

II

a

b

u

at

qi

Fr

u5

i r.r

pr

hcr

flir

a9:

tht

E\E.i\\'e l

me,

con

p)-ri

suct

the

is u.

oflrl'illcart

che.r

Cfetc

gooc

poui:

mal c

coll\'r

u'ithincre.

PERI

Perlit,

made

t64 THE BREAD BUILDERS

BASALT

Basalt is a dense and hard volcanic rock,

crushed and sold as traprock and manufac-

tured traprock sand. It is good fbr heat resis-

tant, high thennal mass concrete r'vhen mixed

n'ith calcium aluminate cenents.

GRANITE

This is a strong, igneous rock containing 20

to 50 percent quartz, held with other crys-

talline minerals in a granular arrangement.

It is moderatel,v dense and modcratel.v heat-

stable.

OI,N,'INF,

Olivine is a rock found u'ith basalt, serpen-

tines, and soapstone in areas of past I'olcanic

activit)'. It is ofien used as an aggregate irt

refractories and high-temperature concrete

because it has verl' little thermal expan-

sion and good resistance to heat. It is very

dense-sometimes or,er 3.5 times the densin'

of r.vater. Oven temperatures do not usuallv

require such specialized aggregates, but ol-

ivine sand is used b)t so-e manufhcturers ofprecast refractory oven components and itcould be used to increase the mass of an1'

masonrv layer. Because it is used in fbundrv

operations, it is u'idell' available.

QUARTZ

The most common mineral on Earth, quartz

is silicon dioxide , rvith a densitv of 2.65 times

that ofu,ater. When heated to 1,600 degrees

Fahrenheit (870 degrees Celsius) it under-

goes a change in crystal structure) with a l5percent change in volume. This temperature

may well be reached at the inner surface ofan oven, so quartz aggregates should be

avoided for high-temperature use unless, as

in high-fired brick, an.v quartz present has

been previously heated. Quartz is a compo-

nent of granites and is a u'ater-carried deposit

in manY other rocks.

SERPENTINE

Less dense and softer than olivine , this is or-rc

of the minerals commor-rl-v used in Europe in

past \re ars fbr building or lining ovens and fbrrrraking urns, vases, and elvers. Although it is

closelrr related to asbestos, there is no particu-

lar health risk in non-fibrous serpentine.

SOAI'STONE

Soapstone is very dense and resistant to heat.

It is often used fbr the hearths of pizza ot -

ens, but it should be covered r,r,ith firebrickin bread oven hearths, as it passes too mucl.t

heat to the bottom of the bread. It can bc

can'ed into beautiful dooru'avs and outerheartl-rs.

STONE

Stone, as crushed rock is commonlv called, is

usuallv n-rade bv mechanicalh. crushing hare'l

rocks. The resulting stones are screened tcr

size, and have sharp edges that interlockwhen used as aggregate. This makes con-

cretes made from stone stronger than sack-

mix concretes made from rounded gravel.

Fleat resistance depends on the tvpe ofrockused.

GRA\'EL

Gravel is a natural product ol generalh'

rounded small stones that are sized accord-

ing to the size of wire screen they u'ill pass

through. Gravel is a common aggregate fbr

concrete, but tensile and shear strength is

r64 THE BREAD BLTILDF-RS

=!-F

:rot as great fbr concrete made $'ith gravel

rs it is for concrete made lr'ith crushed rock.

]ccause the stones do not interlock. Gravel

-isually represents a mixture of rock tvpes.

:.nd the thermal resistance and expansioi-t

--ualities of the rock cannot be predicted.i-or these reasons it is probabl,v better to,-se a knorvn tvpe of stone or crushed rock:r concrete that rvill be used in high-heat

:rrts ofovens (such as a refiactorv concrete.:iposed to flame). Some gravels are quite-.r)nogenous and resistant to heat (like the

::mous grat'el in Devon that was used as

':qregate to temper the cla,v ovens made by:re potters there).

: \PANDED CLAYAND SIL{LE

--rp:rnded clal', slate, and shale are light-ri ght. insulatin g, heat-resistant aggregates

:'-rde bv rapidly heating clav and shale that- ,ntain carbon and sulfur (especiall), iron:',rite, or fbol's gold). Gas is generated at.--;h a speed that it expands the mineral as

re material becomes glassv. This material. used in such huge quantities by makers

: iightr,veight concrete block that the,v

:-l usuallv give 1.s11 as much as vou can

-::t a\\rav in a small truck, or sell it to lrou,:caplv At 90 pounds per cubic fbot, con-

..-:te made rvith this material can provide

- od ler.els of compressive strength (2,000. :rnds per square inch, or psi) rvith a ther--ii conductivity that is less than half that of- rventional concrete. It can be combined

::h other lighnveight additir.es to further. J:ease insulation values.

:3.LITE

- ::iite is a lightrveight insulating aggregate- :t1e bv heating volcanic glass quickly to

1.600 deerees Fahrenheit, rvhere it pops as

\\'ater \-eporizes, fbrming tiny bubbles. Itcan s'cigh trom two to twentv-fir'e pounds

per cubic fbot (pcf) and is not affected by

temperatures to 1,600 degrees Fahrenheit.

Perlite concrete as light as tu.enty-fourpounds pcf are extremelv good insulators

and retain compressive strengths of 200 psi,

about that olextruded styrene insulation. Amix of 1:6 cement and perlite r,vill give a 24

to 30-pound pcfconcrete. Adding expand-

ed shale to the mix rvill make a heavier and

stronger insulating concrete, but be sure

to avoid heavier aggregates and extensive

power mixing, which can crush the perlite

granules.

Perlite is not expensive. Because the littlerounded balls of perlite run into cavities like

water, most of it is used to insulate the cores

of block walls. That makes it eas,v to get, butmeans that perlite sold in bags at masonrv

outlets is often coated n'ith silicone, u'hich

reduces its adhesion in concrete. This isn't a

problem *'hen perlite concrete is used non-

structurall)r as insulation, but locate a source

of the nonsiliconized material to use it in a

load-bearing element. *

VERNTICULITE

Vermiculitc is a lightn eight aggregate made

by expanding mica. It forms into little rvorms

and flakes that are similar to but much small-

er than styrene packaging peanLrts. The littleworms are very light and sofi and resistant

to heat; the,v fill cavities almost as well as

perlite. Vermiculite is less easily available, as

some of it is contaminated rvith small per-

centages of asbestos. IJse a mask r'r'hen vou

pour ltny particulate masonry product.**

*Perlite shouldconform to ASTN{ c

549.Ir is also avail-

able in a rigid fbrm,.q.srr,r <: 612.

* *Vermiculite

should conform toasru c 516.

MASONRY MATERIALS, TOOLS, AND METHODS t65

Mnsonry Tools nnd Method' over the wheel r'vhen the handles are lifted'A rvheelbarrow is good for mixing concrete

It is not feasible or appropriate to describe and mortar by hand and for carrving con-

all the techniques ol masonrv construction crete, sand, and other materials to r,vhere

i-,

-;

-:.

::--:,=,i-

r- L

i __

--:,:-,

:', !i':l a--

a:;

' .-:

,-:

1r

and fbrmrvork in this book.

Good, basic books are avail-

able at the libran' or car-r

be purchased at a masonr\r

suppl,v yard, lumberl,ard, orbookstore. Consult one ofthose texts as a supplement

to this book. What vou doneed to know. horvever, is

r'vhat tools ).ou 1r'ill need.

CEMENT MIXER

Although a mechanical mix-er ma\r be used to mix the

mortar and concrete for an

oven, the small quantities re-

quired mav also be mixed bt,

hand in a trough or u'heel-

barrorv. The entire amountof concrete and mortar that

The trarlition ofwearing vnTrta?/-

bonrds (witb a tnssel

on top to signify n

trail of rnortfr.tf

fnlling off the boord.)

goes ba,ch. to

the gradwetioncerelnonies of the

m.idd.le a.ges, wl,ren

rnnsTns were vna.d,e

rwa,sters of their trod.e.

.:/

thev are needed.

TROWEL

It is conr.enient to ha.i'e three

trorvels on an oven job: a

triangular traditional brick-lal,'er's tror.vel, a flat con-

crete finishing trorvel, and a

notched tilesetter's trorvel.lrhich is used to score the

surface of the sand and clallayer on u,hich the hearthbricks are set.

Along with vour trowels a

fe'iv pie ces ofplwvood measur-

ing 18 to 24 inches on each

side *,ill come in handv as

mortarboards from u.hich r.ou

can trorvel up mortar as neces-

sarlr. Apparentlv the traditionof w e aring mortarboardsgoes into an oven is rather small, and its use

is spread out over several davs. Therefore, itis not too much to mix bv hand.

SHO\EL

(with a tassel on top to signift a trail ofmortarlalling off the board) goes back to the gradu-

ation ceremonies of the middle ages, r,vher.r

masons rvere made masters of their trade.Cements and aggregates are usuallv mea-

sured by the shovelful, using a square or IOINTING TOOL

round shovel that can also be used to slice Youdon'tneedoneoftheseforinteriorbrick-into a bag of cement or to clear away the lvork. Get a mason's or tilesetter's sponge

topsoil for a foundation slab. You have to instead. Tooling joints is a good idea fbrhave a shovel, and it is best to have both exterior bricku.ork, as the compressing and

types. sliding action helps seal the mortar against

\\'ater) and forces the mortar into a tighterWT{EELBARROW bond u'ith the brick. }ointing tools are avail-

This means a concrete t,vpe of rvheelbarrow, able in several profiles, so be sure to choosc

rvith a metal or plastic pan that is balanced one that makes a pattern 1'ou like.

t66 THE BREAD BUILDERS

i.:

':r i

.]ONGE

- ilesetters finish off grout lines bv su'eepinS

:rem gently rvith a damp sponge after t}-re

j:out has partiallv hardened. You cirn clo the

'rirle tling r'vith the mortar in interior brick-

'. ork joints. Just don't r-r-rake the sponge too

' ;t. u'hich r,vould make a mess of the joint

-:r.1 brick and also l'ash some of the cen-rent

.-:r.1 strength out of the mortar.

. :\-EL

- lis job requires several 6'pes of levels. Test

:..lir-idual bricks fbr ler,el (the eve can lie),rtl-r a plastic or metal torpedo level. The

r:gser the bubble, thc better. Typicall,v these

:" els are the length of a brick, so thev can

:: placed on a brick ll.hile it is tapped level

',:th the trorvel handle or a x.ooden mallet.

lhe tbundation fbrms ma,v be leveled u'ith a

',.rter level, a builder's optical level, or eten

'. rth a four-fbot level taped onto the edge of. :traight piece of 2 x 4 lumber; the slab is.:rall enough that a small deviation liom ab-

',rlute ler,el n'on't matter that much. A nl'o-: ,ot and a fbur-foot ler.el u.ill come in handv

: 'r leveling and plumbing the block rvalls as

:rer- are laid.

].1,\SON'S CORD

\l.rr-ri. people find it conr.enient to lay out

'qllare, ler.el, and plumb lines to guide con-.:ruction with brick and block. This is donei ith sturdy, colored string, stretched be-

:'r'een stakes or betrveen bricks set at each

.:'rd of a course of bricks to be laid.

H-{LKLINE

\ chalk line is convenient for la,r,ing o.r, ,n.rattern ofthe r,r'all bricks on the hearth bricks,

be tir:c ti.re u'alls are laid. This is not critical;

.r thick pcncil and a straight edge mav serve

ls ri e 11.

\\'OODE\ \L\LLET

f 59 I ,,r'ooclen mallet to tap brick ar-rd block

ir-rto pl.rce.

THR-EE POUND FLAT{MER

Use l three-pound hammerlrith a brick set to

cut bricks to size . and to rnake half-bricks for

corners. A three-pound hammer u'orks bet-

ter and is safbr than an ordinarv carpenter's

hammer for this job.

BRICI( SET

A brick set is a big blunt chisel that is used to

score or stress bricks ur-rtil thev break along

the line. A brick should be placed on a piece

ofl'ood or a somen.hat vielding surface (soil,

sand) "r'hen

it is hit. Flving chips are clritwl?t

and protective lenses are a must.

I]ACI( SAW

You need a hack sa\\r to cut reinforcing bar.

Basic Corpentry Tools

Carpentrrr tools are necessar\r on this ma-

ror-t11' job to build forms for concrete, to

make braces, and to build forms or center-

ing for brickrvork. A circular sa\\', some saw-

horses, hammers, tool belts, squares, measLlr-

ing tapes, r,r'ood cl'risels, and so fbrth are all

needed.

Nolr' that I'r'e previeu'ed the basic eie-

ments of a rrrasonrv oven and the tools and

materials required to build one, it's time tostart construction.

It'

L.

I

NIASONRY I'IATERIAI-S. TOOLS, AND TIETHODS r67

MATEI€\LS LIST FOR 32'x36" OVEN

Exclwsiya offownd.otion slab, insalation, encloswre, wnd roof

Concrete

Hearth slab: Six 90-lb bags of sack mix orequivalent concrete-see text

Oven cladding: Ten 90-lb bags of sack mix orequivalent

Concrete blockFor base 38' high nt beartb: Fifty-three blocks

16" x 8" and two blocks 8" x 8"

MortarPortland mortar to lay this amount of block

and filty bricks (four sacks mortar mixapproximately)

Portland fireclay mortar to lay one hundredtwenty-five bricks OR

Refractory mortar to lay one hundred twenty-five bricks wirh r/+" joinr lines

(Fireclay mortar willl require one sack Porrlandcement, one sack fireclaS and thre e f 00-lbsacks of fine mortar sand)

Reinforcing mesh

Oven cladding: 6' x 7'approx. of 6" x 6"l0-gauge

Reinforcing barHearth slob: 6O' of s/e " bar (20' lengths

preferred )

Blocbwnl[s: (optional) I2A' of 1lz" bar

tl{trl

llI

I

I

ILumberHearth slab forrn: One shee t of 314 " CDX

plyrood; four 8' lengths of l" x 4"softwood

BricksH ea r th : Ninety-six standard-dury fi rebricks

Oven: One hundred trventy-five best-quality redbricks ( l0% less if using firebricks, I0% moreif using modular-size bricls)

Owter arch and flue fhroat: Fifiry best-quality red

bricks

Chirnney: flue tile and red bricks to suitOuter hearth; bullnose brick or stone slab to fitBelow owter hea.rth: Sixteen red brick splits or

pavers

LintelsFor block base: Two 2" x 2" x 3/ro " angle iron

64" long()ven doorway: One 2 " x 3" x r/+" angle iron

22" long

FoilBelow open clwdd.ing:Two rolls healy-duty

house-hold foil

t68 THE BREAD BUILDERS

VI SIT

CAFE

B€AUJOLAISM en d. o cino, C oliforni a

rf Hrur. HouRs oN \ITNDING RoADS up the scenic route from San Frar.r

I cisco, Chris Kump and Margaret Fox work day and night to turn out

memorable meals at Cafe Beaujolais in the North Coast town of Men-

docino. Chris grew up in a chef's family and didn't start to bake until he

rvas in college, although he remembers visiting Lionel Poilane's basement

oven in Paris as a bog and always held the visual and gustatory memory

ofhearth-baked European bread up against the bread that u'as available

to him on the North Coast.

At first Chris and Margaret tried to bake in the restaurant's ovens, but

try as they might, it rvasn't great bread. Chris learned about Alan Scott and

began negotiations for an oven, but was inhibited by the cost not only ofthe oven, but of a building to put it in and the $.ages of the people who

would bake in it. Then, in a farmer's market in a little village in southern

France, Chris sarv a plume of smoke coming out of a shabbv trailer witha line of people outside it. In the trailer was a brick oven, and in the oven

was a batch of the kind of real bread that Chris had to ltave at his place . He

came home and said, "If he can cook bread like that in a trailer, I'm going

to build the oven!" Chris got back in touch u'ith Alan and they decided tobuild the biggest oven Alan had done up to that time (4 x 6-foot interior)

and to do it as a student rvorkshop to offset some of the cost and increase

the excitement. They named the ner'v bakery the Brickery.

The Cafe already had a walk-in cooler in an adjacent shed so the

Brickery construction was a renovation and addition on that shed, creat-

ing both the bakery and a prep room for the Cafe. The face of the oven

is on the short r'vest 'lvall of the bakery room) with the mass of the oven

outside. The south r,r'all of the bakery has r,vindorvs looking over the or-

ganic garden of the Cafe, down toward the Little River cove. The room

is oblong and open, to allorv free use of the peel, ash rake , and hearth

mop. There is a skylight to reduce glare and the room is full of natural

light, with a concrete floor, a homemade proofing cabinet, one sink, and

two Formica-co'r'ered counters. The proofing baskets are stored in a set

of shelves over the counter and the sink, the bagwette pans on another

shelfnear the proofing box.

The Brickery runs on a nventv-four-hour cycle , six days a week; most

of the bread is naturally leavened. Until 1996, the levuin was made in the

t69

VISIT

CAFE B€AUJOLAIS

Chri.s l(wrup ond MargaretFox, M en rl i ci n o, Cal iforn i a.

Er i-\l!i.iV i;

morning-doughs containing 30 to 35 percent of this lepainwere made upat night by the restaurant staff, well after the bakers had gone home, and thisdough had most of its primarv fermentation in the rvalk-in cooler. Doughmixing by the cooks led to some variabilitv in the doughs and rvas a strain onthe restaurant stafI, distracting them from their primary duties. Because thereare three or more naturallv leavened doughs prepared each day and because

they use aL o.atzlyse to achieve a well-hydrated dough, this evening rvork tookup to t\,vo hours. In 1996, thel'changed to a dough process similar to thatdescribed by Nanry Silverton, and they changed the timing of their retardingstep from primary fermentation to proofing.

Nor,v doughs are mixed in the early morning by the bakers, after the firsrbake of loaves is in the oven. Onlv the leavens are mixed in the evening, a_r'rd

this chore is relatively brief. By 11 a.rnr., the doughs have had their primarrfermentation, rounding, and shaping; after one hour at room temperature, ali

ofthe proofing baskets are put in the cooler, to be taken out and baked the

next morning. Aside from the naturall,v fermented breads, the most popular

ltilil

vI

t

*I

$/{//l

170

,ii

l

i:il;:

I ir(a:

::.-(e$

,r.,Ai

-{kf,c,

!-s

bread at the restaurant is a yeasted Austrian Sunflower Bread that contains

ten kinds of seeds or grains; these require soaking to soften and are mixed

together and wetted in the evening so the dough may be made up, fe rme nte d,

and baked the next day.

For a number of years, the Cafe Beaujolais oven was fired with fireplace

logs first thing in the morning, after the wood had dried overnight in the

cooling oven. This delayed baking for several hours, the heat on the hearth

\r'as uneven when baking began, and the wood sometimes overdried. An

or.ernight firing program was developed in l996,inwhich the oven is lnaded

tstill with fireplace-sized wood) at the end of the baking day, but not lit. Thatsood is dry (but not excessively) by the time the evening staff comes in tomix the leavens. They light the oven; when they leave it is burning brightly,

allowing them to place a draft door over the oven doorway, with room at

the top for smoke to exit, but with control of incoming air (with adjustable

air intakes on the door). This gives a burn of about six hours, allowing more

bakes the next daywithout as much use ofa supplemental gas burner berween

bakes. The oven has a portable gas jet that can be fued in the oven for fifteen

to rwenty minutes to raise the temperature by 25 degrees Fahrenheit (14

degrees Celsius) if there is a pause in the baking and there are several loads

still to go. The overnight burn also allows baking to start as soon as the oven

is cleaned out and rested for halfan hour, baking the retarded loaves shaped

the day before.

Altlrough the hearth heat is now even. the re is a tendency for the hearth

to be a little overheated relative to the dome. Since the first bread baked each

day is a load of baguettes, thjs extra hearth heat has not been a big problem:

ttrey are baked in perforated stainless steel pans that hold them up off the

hearth a little. By the end of the morning there is plenry of bread, not iustfor the restaurantl but for wholesale clients (stores) and for retail customers

nho buy bread from the restaurant secretary.

What are the things that really work about this operation) First of all, Chris

and Margaret could not have had a first class restaurant without first-class

bread, and now they have it. Secondly, the restaurant has to have a secretary,

and it is not too much of an interruption for the secretary to sell some bread

in the middle of the day-but it would be too much of an interruption forthe baker to sell it all. Also, the restaurant is staffed at night, and the baker

t7l

Lonpes on a poel wnl, be

sprayed with nratey, then

dusterl with seeds before they

nre bahed.

can be home when the leaven is mixed fbr the next day. All of the staff get

to have some control over their work hours, even though bread is available

by mid-morning.Wrhat are the things that don't work so wellf Well, the Brickerv is only

about a break-even proposition. The market in Mendocino is small andthe labor is hired, so a typical one hundred and fifty loaf day may notbreak even. Tl-ris is made up on the weekends and in the summer, butonly barely. It would also have been nice to create a seasonal n-rorning andlunch place centered around the oven, a service room for coffee and bistrofood, but the construction cost u,'as just too high. A trial some years ago

of oven-bake d pizza for lunch just rvasn't profitable without the ambiance

and seating to go with it.Overall, though, everyone at Cafi3 Beaujolais is pleased rl,'ith the Brick-

ery. They love the bread they sell and eat, they don't lose money, they are

fascinated by the process) and evervone gets some sleep at some time ofthe day or night.

JLISi:t:

for ',

lirr : .--

cle s c:r:ovetl

rion , :lltoSl:give ;ancl k:,bur' 'r-:

make :thou:'.nrain :--

Ft::

ri'alls ::llleas.:f.

firebnc..1L

172