masonry materials, tools, and methods
DESCRIPTION
Chap. 8 The Bread Builders: Masonry Materials, Tools, and Methods. by Daniel Wing and Alan Scott. Chelsea Green Publishing Company, (c) 1999 Daniel Wing and Alan Scott.TRANSCRIPT
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