preparing to build a masonry oven

7/27/2019 Preparing to Build a Masonry Oven

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CHAPTER SEVEN

PREPAruNC tc BIIILDAMASONTgOVEN

ecause most people these da1,s haveiittle experience with masonry con-struction and have neither seen nor:,*r: f, masonry oven, I think it wise to pro-'r:i en introduction to the choices involved.l:s chapter will review the features of di-"::-j'u'-fued masonry ovens) and the safety: :rsiderations inherent in their constructionli[:\J USe.

lrrt Safety. n, :rs built to plans similar to the ones in thist':,, r have been approved by building inspec-r,:r: h many states under the portions of thenuJng codes that deal with fireplaces, butnl ling codes do change and interpretation

,in,: .nfbrcement of these codes varies greadyr.. r: jurisdiction to jurisdiction. Thereforet: t- ttutst discuss your intentions with thetn'ui;ing code enforcement team in your area;r:rr " \-ou build. Ifyou live in an unregulatedun:;- shorv your plans to the chief of the fire

department, and document your conversa-tion. Failure to show reasonable diligence infire safety could void your fire insurance. Ofcourse) in no case can I (nor the publisher orany other party) be considered responsiblefor your actions, your oven, or any problems(such as a structural fire) that may result frombuilding an oven-you have to assume theresponsibility yourself, and acr according tothat burden. I will get you started by describ-ing some common code requirements laterin this chapter.

Design Lessonsfoo* Historicol OvensYou know that traditional bake ovens arecalled internal combustion, retained-heat ovens (or direct-fired) because woodis burned, the ashes are removed, andthe bread is put into the fire chamber tobake. Like traditional rowboats and handtools, internal combustion ovens possess a

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functional elegance honed by hundreds of],ears of trial and error. Every element ofthe oven is necessarl, and errery necessaryelement is in place.Although ovens can be built (and used)that do r-rot lbllorv tl-re guidelines given inthis chapter, they may have drarvbacks. Forexample, over-rs built with a rectangular oroval floor plan (like the one in this book) aremore practical to load with loaves than roundovens, even though lou'-roofbd round ovensare just as fuel efficient. Orrens with accessoryflues and no way to reqrgls the heat carriedolrtin the exhaust are Lrsuallyless fuel etncientthan ovens that vent out the door.

Manv old books refer to the desirabilityof building an o\ien s,'ith an oval floor planand a lor,v door, r,','ithout explaining rvir,v.Lise Boilv and Jean-Frangois Blanchette (intheir 1979 book The Brenrl Oyens of Qrtbec)were the first to make a sumrharv of the de-sign criteria fbr successful ovens. B-v makingdetailed measurerrrents of scores of existingovens built of clay in eastern Canada, the1,distilled for the first time the principles thatmake these things r,vork. It is fortunate thatQuebec ovens are built to a vernacular designbrought from France three hundred yearsago arrd little changed over timc. since mosrsimilar ovens r,vere replaced long ago in urbanEurope, u'here larger hybrid ovens operatedby apprenticeship-trained bakers became thenorm.

Oven Essentials-Intewcally Fi,red. Ot ensInternally fired ovens can be used in bothdirect-ireat and retained-heat methods ofcooking. By direct heat I mean that a fire

continue s to burn in the oven chamber r,r.hilethe bread is baked, as in the Indian tandoor o:in Italian roasting alndpizza o\rens. Retainedheat rleans that the fire is removed befbrcthe food is cooked. This is the r,vay loar.es ofbread are baked.

Because retained-heat ovens can onl',deliver heat drat rvas stored in the masonr-,as the oven r.vas fired, these orrens must behealy and thick. Their mass must be sufficier::to store enough heat to bake the brea.rThis requirement for oven mass is one ,-,the factors that affbcts retained-heat o\-e ,useftilness and efficiencl', but oa1t.t fxgtt-,::

1 7An oyen in which the wolk and lmarth are to,,thin won't retain enough be at for baking lon.1'breads.

An fficient d.irectly-Jired open will hape n du:that is obout 63 percent the beight ofthe hriii,its d.ome.

z

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.re also important, such as insulation and-re d1'nx11ics of oven air flou'. Even more.rportant is the operation or management of:-r- oven (chapter l0), because firir:rg a cold

en to baking heat requires heat that will-:-, er be recovered bv baking bread. (This-.:s been referred to as the preheat b,v oven-.icienc,v researchers.) If at the tirne a fire is:i.lrtd an oven is still warm from a previous-.e. but not hot enough for baking, only a,::rall firing is necessary to get it ready for use.- his marginal or incremental heat could be-, lcrl the baking heat.

Tl-re eficiency of a masonrv oven can be

'. ,)i1e7x that is too flat will lose too wwch of its.;; out the door, and. the d.oor" will be too low for...,)in!.

trtn that is too tall will haye cold spots in the..i the rLonoe thtLt nerer get fwlly heated..

a hard number to pin dou'n, as it is going to\rary with patterns of use el'en in lhe sameoven. It is alu'ays greater when an oven isin daily use because no preheat is necessaryA retained-heat oven designed for daily usema-v therefore be especially massive, so theheat storage is great and the oven tempera-ture is stable. For intermittent use, overallefficienc.v w-ill be higher in iighter ovensbecause the or.en must be preheated eachtime it is used; the preheat cost is less for aless massive or.en. The drau.back of a lightoven is that the oven temperature u'ill be lessstable if it is used in a retained-heat mode-itwill cool off more quicklv as it is used. Theoven r,r'ill need to be fired more often if agreat quantitv ofbread is to be baked, eventhough a light oven may be perfectly suitablefor prolonged use in a direct-heat mode (forpizza, for example ) . *Each penetration into an oven's bakingchamber represents a potential site for losingoven heat and steam, so an internal combus-tion oven should draw in air and exhaust outsmoke through the same door. Ifthe oven hasa chimney, it should be in front of and abovethe oven door. Ifan ash-drop slot is provided,it should be outside the door as well. Presen-ing the sealed integrit,v of the baking cham-ber permits retention of heat r,vhen the fire isremoved and retention of steam during theearly phase of baking.

This lack of air vents and intemal chim-neys in an internal combustion oven placesrestraints on its geometry', since air must flowin the open doorlvalr, lan the fire, heat theoven structure, and flow out without restric-tion. A too-low oven roof or a too-high ovendoor will allou. the fire and its heat to spillout the oven doorway and up the flue. l{eat

A *Eric Shirey andfohn Selker mea-sured the bahingheat eflicienciesofseveral uninsu-lated r.ernacularretained-heat ovensin undevelopedcountries (ovens inuse e\rery day) andfound that theseaverage about 0.45kg offlour bakedper kg ofwoodbr-rrned. Eflicienciesin large externallvfired or.ens (whiteovens, in u.hich thefire and smoke clidnot go through thebaking chamber)were much greater,but rvhite o\rens aremuch more com-plex and expensiveto construct.

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wiil be r'vasted. On the other hand, an exces-sivell, high roof-like the roof of a typicalhemispherical oven of the Southr'vest-willcause the smoke to stall unless air vents areprovided. Firing will be dilficult and the roofof the dome r,r'ill be underheated. (You cansometimes see a coating of soot in the domethat shorvs that part of it rvas inadequatelyheated.) Ovens that are deeper (longer) than

Stat,t the f.re in the front of the oven. Add woodwhen the ft e is bwrning well, and. let it burn allthe way to the boch of the ot,en.

they are wide tend to drar,vwell and are pror-abll' p6.. elficient than round or square o." -ens, although careful construction ofthe are;just inside the door ofa round oven can oti:e:this problem someu'hat.Boily and Blanchette determined br- &-rect measurements that there is a critical be:rratio between the height ofan oven door anithe height of the oven dome. That ratio i:63: 100, or 63 percent. (Folk tradition some-times holds 4:7 to be the ratio, which is 5-percent-quite closel) This represents d:eaverage ratio for Quebec ovens that do nc,:har.e supplemental airvents, lvhichw.as one c,rthe r'r'ays that Boily and Blanchette were ableto determine which Quebec designs lr,orkeibest. The further from these proporrionsan oven is, the more likel,v it is to have-


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pleasing. This is possible because the basicmaterial of the oven-ciar'-is a plastic ardforgiving medium that is eas\r to form intosmooth cuffes and shapes. Unfortunately,,clay has some drawbacks for oven building,even if reinforced with stone or brick:r Good native clay can be diflicult to findand is hard to dig out and prepare in thequantities needed for an oven.. Clay is warer soluble, and the outside ofthe oven will never get hot er-rough tofire the clay into terra-cotta or brick, soit r,vill soften and slump if it gets wet.. Clav is not a good insulator, so the ovenwill not hold heat well from one dav tothe next.r Some clay ovens wear away from theinside (drop pieces of clay) and eventu-ally need to be repaired.

Some of these problems can be over_come when a clay oven is made of temperedhigh-temperarure clay and fired in a kiln,l-hen it is built up of individual hunks ofclay soil that have been dried and are thenbonded u'ith wet clay (adobe), or whenthe clay oven is roofed over. In Mennonitecominunities on the Canadian prairies theoutdoor ovens were built by farm women,using native cla1. xs mortar and claddingtbr an arch of used bricks. The ovens r,verethen col'ered with burlap, pasted to theouter laver of clay with a mixture of flourand lvater. When this rvas dry the oven was',r-hitewashed, giving sufficient rain protec-lion lbr a dry rsgien.

Although these techniques wili extend thelsable life of a clav oven, for most intents andpurposes it is more practical to build ovens

out of more durable and easily availablebuilding materials. The oven constructiondetails I describe later are suitable for an ovenbuilt out of red brick, firebrick, refracrorycements) stone, concrete, steel angle, and soforth, each used in such a \l/av as to providea balance between aesthetics, cost, and ef_ficiency.PROPORIIONS AND MATERIALSFORBzuCI(O\GNSPractical experience has shown that a ceilingheight offifteen to eighteen inches is optimalfor baking loafbreads, because a lower ceilingwill necessitate an impractically low door, anda higher one will reduce the moisture contentaround the loaves and reduce crust fbrma_tion. (This rule does not have to be follorvedso exactly for an oven built primarily for pizzaor for mixed baking and roasting. The doorand dome may be somervhat higher, but stillat the 63 percent ratio.)

Experience also shows that the thicknessof uninsulated masonry in the hearth or floorof the oven should be slightly greater thantl"rat of the oven walls and dome, so that alittle extra heat fiom the hearth can flow upinto the oven during the baking cycle. Heatfrom the hearth is very important ro goodbaking ofloaf breads.

A masonrv thickness of eight inches in thehearth and about seven inches in the domervorks well for an oven that is used intermit_tentl),', or is used for both bread and pizza(the fire is pushed ro the back of the ovenbut continues to burn rvhile the pizza bakes).An oven used only for pizza can make dou,ith tr,vo and one-half to three inches ofmasonry in its walls, and five inches in thehearth. (This may nor pass rhe building codePREPARING TO BUILD A MASONRY OVEN IJJ


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Richard. Fteetnnn has hpo brick oyens in ome: nn innet'at'ch of brichs, n layer of insulotion, and. anenclosut'e of brichs.

in some areas) and may require the use of amuch thicker outer oven, or enclosure. ) Sucha thin oven will be easy to bring to properheat. An oven used to bake loaf bread on adnilybasis should have at least ten and one-half inches of masonry in the dome) and alittle more in the hearth.

A good brick oven is insulated below thehearth mass, all around the walls, and abovethe dome mass. This allows the use of thegraduall,v decreasing heat in the oven over aperiod ofdays (for cooking casseroles, dryintherbs, and similar uses). The heated mass ofthe oven should be isolated from the foun-

dation to reduce I'reat loss and to preventcracking of the fbundation when the ovenis heated.

Modern internal combustion ovens willretain the advantages of their predecessorswhile avoiding the drawbacks mentionedabove by employing these critical features:. one door and no vents;. external chimneys and ash drops;. the 63 percent ratio of door and dome;. baking chamber is deeper than it is

wide;. oven mounted on a slab that can expand134 THF, BREAD BUILDERS


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and contract without crackinq the or-er.rfoundation;. a smooth neck to permit unhindered airflow and easy ash and bread removal;. r'vell insulated;. mass and wall thickness appropriare rotheir intended use;r thermocouple (heat sensor) svstems toassess firing ar-rd baking conditions;o firebrick hearths that transfer heat to thebread at the correct rate $.hen the ovenis properly heated.

Externnlly F'ire d. an.d Exh auste d.Ovens-White OyensThe principles for the construction and use ofwhite ovens are different than those fbr theinternally fired black ovens, and a detaileddiscussior-r is bevond rhe scope of this book.Such ovens rvere once common, and some arestill being made (see the visit to HomeFiresBakerv). In good designs the thickness of themasonry ofthe oven serves to temper the heatdelivered, as urell as to store it-several inchesof masoilr\r (at least tw.o inches) separates thefire and its exhaust from the cavity of theoven. The added cost and complexity of thisflpe of oven construction (tvhich re quires afirebox, a double n all, and nrultiple flues andciean-outs, all of lvhich mlrsr be built by orunder the guidance of an expert mason) onlrrmake sense lbr a commercial oven, or if a ma-sonry heater is being built at the same time,incorporating the oven. Masonry heaters areusually expensive, but including an o\ren maycreate little additional expense.

Plnnning Tour OuenA little thought ahead of time will save you alot of head-scratching later. Let's look at themajor areas you must consider.

SIZE AND STT'I-EThe size and style of your oven must be ap-propriate for its intended use. A brick ovenshould not be depended Lrpon to heat a roomor a house, unless it is built as part of a ma-sonry heater. It is possible to recover someheat from any indoor oven when it is not inuse, but this is a secondarv effect. Ifthe pri-mary goal is house heating, several designs ofcommercially available masonry heating ap-pliar-rces incorporate a small oven, and thereare masons in the United States u'ith experi-ence custom-building masonry heating ap-pliances on-site that have o\rens, or in whichthe firebox can be used as an oven when thefire is removed. Another possibility is to builda small oven (as described in this book) andhave it share a foundation but use a separateflue in the chimney ofa neu'fireplace orr.voodstot'e. All of these are better $ra).s to heat ahouse than to try to build an or.en accordingto the plans in this book, and then try to heatyour hor-rse u'ith it.* Thal said, a masonryoven is the bestw,ay to bake bread and cookother foods you need, and it can be a pou.-erful architectural statement in or outside ahouse or restaurant/bakerlr.

Sizing the oven to y6llf intendecl r-rse isimportant. A 4 x 6 foot or 6 x 8 foot ovenmay bake ten large pizzas or ninety loavesof pan bread at a time, and will ahvays re -quire more r,vood than a small oven. A moremodest oven makes better sense for domes-tic use, indoors or ollt. Masonrl, ot ens work

*Members of theMasonry l{eaterAssociation aresorted bv geographic area ontheir Internetnebsite xt: \\,\r.\...mha-net.org. Seethe Sources list-

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i -ih -st\tle\ lJtnter,Dou11 Wootl,iuhe otem

itt Jtreplace

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better lbr cooldng loaf bread u'hen they arefully loaded, or nearly so, since full loadingkeeps the moisture level up in earlv baking. Asmaller oven will bake just as \\,ell as a largerone, bur it u4ll bake a smaller load. As Selkerand Shirey point out, the geometr_v ofa domeshape means that the radiant heat reachinga loaf from a small oven is the same as fora large o\ren, if tlle masonrv is equally hot(see bibliography). Of course, the conduct-ed heat liom the hearth is dependent on itstemperature and the specific heat ofits brick,not on the size ofthe oven. You should avoidan excessively large oven; if necessar,v, a smalloven mav be refired (reheated) if you oc-casionail,v need to bake a larger quantity ofbread.

O\EN SIZING BY INTENDED USE\\4tat do lrou intend to bakef In general, thosewl-ro wish to make predominantly pizza u'ili\vant the widest possible oven and the lvidestpossible door (and thinner masonry in thedome), r.vhile those u.ho concentrate on loafbread will \\rant a deeper, longer oven u,'itha smaller door. Some oven builder/ou.nershave chosen to build very small or.ens (20 x30 inch) because thev u.ere sure thelr wouldnot \\'ant to cook more than a feu' loaves ata time) onl1, 1e discover that the bread 1r'asso good, thev u.ished they had a larger oven.Besides, it's not easv to leave a fire goingu'hile cooking a series of pizzas in such asmall oven.

The smallest oven AIan Scott recommendsis a24 x 30-inch size, u4rile most householdovens are the size of the one presented inthis book: 32 x 36 inches, with a door thatis 16 inches wide and 10 inches high. Largerfamilv ovens are 36 x 48 inches; interestingll',this is the size of most old flrmstead ovensin this country and Europe, lr.'here all thebread for a famil,v was baked once a \\reek. Byusing modern thermocouples, you can esti-mate hou'much firing you need to bake ser-eral batches once the oven has been heated.Changes in the r,vay you manage your ovenu'ill let you bake two or three times as muchbread as the nominal capaciq'of your oven,u'hen you need it (see "Otren Management,"chapter 10).

Commercial ovens for small bakeries aretypicallv 4 x 6 feet up to a practical limit of6 x 8 feet (iarger ovens are possible, but areusuall1, fired r'vith gas, or are either hvbrid oru.'hite ovens). The maximum practical widrhlbr the mouth of such an o\ren is about 24

.nches. Sor',r'icler, anclirere; ther-as tbr bteaDECIDI\A,L{fERI.IFORAN (The nextansu.er is\-ollr o\-er';lreas: theslabs ar-rd.lome. Tl204 and .temperatlbetn'een tconcreteincreases -use. If th,a feu'tim,crete \\'illgrees Fahstandard lthat just Iit retainsever, \'oLllheat in) arant or b:mav be cthermal cis advisabconcreteding (seeConstanteasier wiitemperarner oven-YoLr plailtime t ort

THE BREAD BUILDERS


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inches. Some restaurant ovens are higher,wider, and shorter than the ones describedhere; they are designed for roasting as r.vellas l'or bread and pizzas.

This same kind of reasoning applies forusing red brick on the oven u'alls and dome:red brick r.r'ill last your lifbtime if you heat\rour o\ren graduall.v and bake a feu'times a

week, but it will probably lastDECIDING ON THE onl1, a few years if the oven isr\{-ATERIALS A fWASOnfy 7ten iS in constant use or is exposedFORAN OVEN thebeSt WAy tO bOke torapidtemperaturefluctua-Thc rrcxt questiolr you mtlst t , , - ^ ^r^ ^-,- ^-- tiorls, especiallv from exces-a.swcr is about materials ficr bread nnd c00k Orner sivewaterspravsormopping.vour o\ren, especiall,v in tr,vo fOOdS yOW rueed: A'nd' In the latter cases, it is bet-areas: the concrete for the it Cnn be n pOWeff^l ter to use firebrick. In someslabs and the bricks lbr the 1 | , lictions that follorv thea.rcnne ctural Llt':'c1ome. The charts on pages Uniform Building Code,204 and 205 shos, that the sta'teywent 0n 07/ oven domes may need to betemperature at the interface OUtSi,d,e A hOUSe Oy l0 inches thick (includingbetr'veen the bricks and the resta,Lrrnnt/bakery. bricks) when lined s'ith redconcrete cladding graduaily brick, and only 8 inches thicklncreases rvhen the oven is in ':/ r,vhen lined with firebrick.,,rse. If the oven is only fired That could be a decidingr tbrv times a week, the con- fbctor fbr -vou, if you want;rete rnn'ill never get much hotter than 450 de- an 8-inch dome. Also, some code enforcers*rees Fahrenheit (230 degrees Celsius), and may require that the outer walls of the oven':andardPortland-basedconcreteu,'illhandle (the enclosure) be 8 inches thick if the oven:rat just fine; even at700 degrees Fahrenheit chamber is lined with red brick, and only 4:: retains 50 percent of its strength. If, how- inches thick if it is lined with firebrick.-\.er, your oven is both insulated (keeping the:eat in) and in use every da1' (as in a restau- SPACE PLANNING::nr or bakerv oven), concrete temperatures Ask yourself r,vhat will be taking place in the:.ilv be excessive, especially in vieu' of the area surrounding the ol'en. Consider that-:ermal q/cling that occurs. In that case, it ovens draw peopie together and become a. edr,isable to use alumina-based refractory focus of activity, indoors or out. It is a good: increte for the hearth slab and dome clad- idea to plan not only the extra space neces-:ig(seethefollowingchapteronmaterials). sary for manipulating the long oven tools,L. .rnstant use (for bread, notpizza) becomes but to allow plentv of room, somervhere-.sier with a thicker ol'en because the oven near, fbr the peanut gallery (people love:::lperatureismorestable. Ofcourse,athin- to rvatch!). It is essential to have a flat sur--.:: oven will be more e conomical with fuel if face onto rvhich you can place dough, pans,

l plan to bahe onl,v one or trvo loads each boards, cornmeal, your fire gloves, and er'-:re vou heat the oven. erything else you need. Ofcourse, you needPRF,PARING TO BUILD A MASONRY OVEN 137


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facadesteel mesh

afus(joirmcchi(onmubui.minthisoraresi


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a masonry chimnel'. In masonrS bothuse a s/r-inch fireclay or refractory linerjoined u'ith medium-dut.v refractorymortar. The wall of the Residentialchimney need onl1, be 4 inches thick(one brick), u'hile an Industriai chimneymlrst at least 8 inches thick. Thebuilding code uses a graph to determineminimum cross-sectional flue area, butthis rvill be met by an 8 x S-inch squareor a 7-inch diameter round flue for allresidential ovens.

2. Chimney reinforcement: In seismicallyactive areas, masonry chimneys must bereinforced n4th steel and strapped tothe frame of the building at each floor,even (in some cases) tied to the ovenfoundation. Regardless of reinfbrcement,in no areas are chimneys aliowed tocarry any of the load of the frame of ahouse unless specificallv so designed andapproved.

3. Spark arrestor: In dry regions code mayrequire a metal mesh spark arrestor if theoven is withiria certain distance of trees,brush, or flammable roofing.

4. Foundation: The stock building codelanguage requires a foundation that isa fbot thick and that extends at least 6inches outside the oven u'all. That por-tion of the code allorvs for exceptions,which you should seek-a foot is thickerthan 1rs11 need, if 1,our foundation slab isadequately reinforced.

5. Clearances: There should be no com-bustible material within 2 inches of achimney, or 9 inches of an oven rvall.This distance can be reduced (under Na-tional Fire Protection Association rules)if heat deflectors are installed. Note

that these distances are not the same asthose that apply to "range appliances"such as r,vood-burning stoves made ofmetal, which have much higher surfacetemperatlrres than the outside of ovenenclosures, and must be much furtherfiom combustible surfaces.

6. Hearths: This section may require thatthe hearth extend at least l6 inches fromthe inner oven door, tvhich is longerthan is practical. This is one area r'vherefireplaces and ovens really are different,and so you should argue if questioned.The fire in an oven is much farther fromthe front of the hearth than the fire in afireplace.

7. Centering: All combustible lbrmworkand centering (wooden work used tosupport arches during construction)must be remol'ed before the oven isused.Use the charts in chapter l0 if you haveto convince the authorities that the out-

side of the oven insulation will not be hotenough to be a danger. These are recordsof tests on installed ovens. Plan to vent thearea betrveen the insr-rlation and the sur-round, regardless ofthe adequacy ofyourinsulation. If any part of the surround isnot masonry) Llse metal studs and fram-ing and insulate with a granular materiallike vermiculite or perlite (preferably witha thin layer of diatomaceous earth rightnext to the r.valls and dome of the oven),u,hich can sift into and seal any potentialcracks. Line 1rs111 enclosure u'ith a non-combustible material before you applyrvooden siding. Consider building an in-sulated masonry enclosure, then strapping

Consi.d.er thoto"pens d,rawpeople

together a.nd.beconoe

n focus ofoctivity, sonllow plentyof roono towork, ond,enobgh for the

pea,nxotgnllery.

r39REPARING TO BUILD A MASONRY OVEN


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the outside of it with metal studs, and put-ting wood siding over that. Be safe.OUTDOORO\TN SAFETYIn most districts an outdoor oven is con-sidered a barbecue (Section 3102.2 of theUBC), and in most districts these are fuilyregulated. You should ask, to be sure vourinsurance is not jeopardized. You may needto follow the same structural guidelines, andyou may need a screen over the top of theflue in areas prone to brush fires. In addition,there may be a zoning issue-you must ob-serve properqr-line setbacks. In an.v case youu'ill still be responsible for any fire you causedue to poor construction or unsafb handlingofthe fire, the coals, or the ashes. Ifthere is nohose faucet nearby, mount a fire extinguisherto the oven base some*,here) to back up yourbucket of water. Watch the oven during theearly part of the burn, r,vhen it might throrvsparks.

Balert, Fires-ttYan't Happen Here !It cowld. happen here. I know of tlvo firesin small commercial bakeries, caused in eachcase by both structural deficiencies and im-proper oven management. Neither of thesefires caused major structural damage, but thatr,vas mostly luck.In the first case the structural problemsincluded both an inadequately thick cladding(that allowed cracks to form) and the use of afibrous insulation that did not seal the cracks,that allowed soot to build up, and was porous enough to allow combustion air to reachthe hot soot. The management problem wasthe routine use (over a period of years) of

the oven to dry rvet firewood. This allowedvolatile wood gases to escape from the oventhrough the structural defects, then con-dense as soot. Fortunatelv. the smolderingsoot in the fibrous insulation made enoughsmoke that the bakers were alerted and therewas little additional damage. The oven hassince been rebuiit and improved, and they nolonger bake (the technical word is "coke" )their firen'ood in this fashion.

The basic cause of the other fire was over-firing an oven that was too small and toothinly clad for the production asked ofit. Thissmall oven w.as often overheated to attemptto get extra bakes from each firing, and theresult was cracked bricks and cladding. Thissecond oven had an unventilated rvoodensn6le5lrls-more no-nos. Although the en-ciosure u'as damaged in the fire, the baken-building was not damaged. Again the oven,the enclosure, and the management of theoven were changed.To revielv: Drying rvood excessively ina masonry oven is not recommended (seechapter 10). Wood enclosures are not rec-ommended unlcss applied or er fireproofmaterials. Build an oven wall that is at leasr8 inches thick. Do not insulare a brick ovenwith loose fiber insulation such as rock woolor fiberglass. Use vermiculite and/or dia-tomaceous earth that will sift into and sealcracks that develop. Loose fill insulation likethese r'von't pass enough air to support com-bustion, either.

The Heabh Depa.rtvnentYou need to get in touch with your loca1health department if you are going to sellsome of yor.rr bread. Rules and their inter-

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r40 THE BRT,AD BUILDERS


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pretations vary too much for yoll to make as-sulnptions. For instance) some states are \rerylenient with small-time producers, and voumay firr4 you can sell quite a few loaves a dayor a week without any interference. In otherareas you are not supposed to sell anvthingrvithout some kind of permit. Regulationsusualll. cover the storage of ingredients, airgaps on the sinks, drains in the floor, sew-ers or septic tank connections, and trash andgarbage receptacles. Find out w'hat you needbefore you set up your baker,v, otherwise yourun the risk of facing expenses iater.* I(eeprodents and insects out of the grain and thebakery area itself.

Some artisan bakers have had troubleu'ith their local health authorities becauseof urooden lvork surf-aces, or because linencowche cloths or baskets are not normallyrvashed between uses. You must realize thatthe person from the health department r'r'illprobably never have seen a bakery like yoursbefore, so )rou must know the codes yourselfand establish aworking relationship with theinspector by pro*ding information aboutartisan baking. (The Bread Baker's Guildof America can provide copies of articleson this subject.) Having the inspector trv alittle of your bread is a great wav to breakthe ice. If the inspector is going to $'ritevou up for things you believe are safe prac-tices, remember that brick ovens and linencouches are probably ruot covered in the codebook, and I knorv of no documentation thatthey constitute a health risk. Don't roll overand play dead. Get an attornelr, if necessary,and go through the appeal process. You rvillprobably win.

Constrwction Prel)tewLet's revier'v the basic elements of 1'e1tt -"-sonrY oven.FOUNDATION SLABThe most practical foundation for an oven isa slab of reinforced concrete, resting on well-drained soil or sand without other lbotings orfrost wails. In a cold climate, the slab shouldrest on rigid fbam insulation or a rubble foot-ing. This will prevent freezing and heavingunder the slab, and will allolv you to omit thecustomary fiost walls.

Commercial concrete is purchased tran-sit-mixed out of a truck, but most comPanieslvon't deliver less than a cubic yard withoutan extra charge. This charge may be reason-able ifyou are not far from the batch plant, orif ,vou need to make a foot-thick foundationunder local code. The alternative is to mix ityourself unless yo11 "ta itt an urban area wheresmali transit-mix trailers are available.ASH SLOT AND CFL{MBE,RIt is best to provide an ash chamber under theoven, lvith masonry r,valls and/or a fireproofmetal container for the ashes that are scrapedoff the floor of the oven after firing. A metaldoor that closes off this chamber will keepchildren, pets, and rain out of the ashes. Thebricks on the floor ofthe oven rest on a bedofclay and sand above a reinlbrced concretesiab, which is supported by the walls on thesides and back of the ash cl.r.amber. The ovenfloor slab is made smaller (shorter and nar-rower) than the oudine of the supporting'rvalls and the slab's grid of steel reinforcingbars is left to extend out above those u'alls

*See rvhether thereis a categorv forsmall kitchens likethose in schoolsand camps-thatcategorr,couldapplv to vou andis usuallr. lessrestrictive thanthe general commercial categor)rAlso check onpackaging rules invour area-somejurisdictions requireclosed bags.

PREPAzuNG TO BUILD A MASONRY OVEN 14I


14/28

tlernents of thethein the oyen

the owterthe ash slot,

the doojamb

original redin the backfireplace of

house are justs'earing out.haven't repiaced

thor,rgh,thet'aren't

s-orse thanll ere ten vearsand mv house

;nore rhan 200rrs olcl l

L42

thechufburhalfpouiof thmorllongof al;dom,ro rhreintiso rhtbil aenoUlinsulaor st(o\-en.nd rest on them. That wav. the slab is freeto move slightly with changes in tempera-

ture. It also means that outdoor ovens maybe fairly easy to jack up and move to a newlocation, to be set on a ne\\. foundation ifneed bc.HE4RIHThe floor of the oven, the hearth, is builtof firebricks, turned on edge; no mortar isused to hold them in place. Firebricks lastmuch longer than red bricks when in directcontact r,vith coals. Although soapstoneslabs make an attractive and durable hearth,they are more expensive than firebricks, andthey store and transfer so much heat thatthe bottoms of loaves of bread tend to getburned by the time the tops of the loavesare baked. Soapstone is fine for flatbread,but rvhy limit vor-rrself to flatbreadl Somepeople sav that firebrick is too porous fora hearth, and recommend some form ofpottery. In practice, though, the heat ofthe next fire rvill burn up any traces of fat

THE BREAD

or other liquids that have dripped onto thehearth, and firebrick is more resistant tothermal shock than pottery.WATLS AND DOA,TEThe inner walls and dome of a home ovenmav be built of hard red brick or firebrick.Red brick is cheaper, attractive, easily avaii-ablc, and long-lasting in this applicarion.if it is not sprayed excessively wirh warer.*Most people use firebrick for the hearth.rvalls, and dome, though, and some masonsare shocked by the idea of using anythingelse. Firebrick is much more resistant rothe type oferosion that occurs on the floorof an oven u'hen r,vood embers are fannedby combustion air, but this only happensto a limited extent at the n.alls and domeof an oven. Firebrick is more resistant tobeing splashed rvith water when it is hot.but even firebrick will not last lbrever if itis abused that wav.The u'all bricks are set vertically, mortaredtogether with a thin iine of mortar so rhar

BUILDERS


15/28

-TI

I13-1 6',

fl ue

the long edges of the bricks face the ovenchamber. This gives a brichthickness of aboutfbur inches. and an additional trvo and one-half to six inches of reinforced concrele ispoured outside them (depending on the sizeof the oven and its use). The dome bricks aremortared into an arched vault, again with thelong edges facing the oven chamber. A la1'erof aluminum foil laid over the bricks of thedome prevents the brick la1'er from stickingto the surrounding reinforced concrete. Thereinfbrced concrete hoids the walls togetherso the brick arch cannot collapse, r.vhile thefoil allorvs the bricks in the dome to heaveenough so that no big cracks can form. Aninsulation layer and an enclosure u4th a brick

::.rrr"".facing complete the body of the

THERMOCOUPLESThermocouples are metallic thermometerprobes that can be buried in the rvall andtloor of the oven. Wires then lead to a gauge:hat will tell you the masonry temperature at.r giance. The det*fls of these devices will becovered in the chapter on oven managementchapter l0), but u'hat you need ro knorv:ere is that it is helpful to have a series of

-hem at various levels of the thickness of thelasonrv. That makes it easv to see when the,r'en has been heated enough and easy to see'-,'hen the stored heat in the masonry is too.)\\-to continue baking. The main drawback:r thermocouples is cost-both the probes.':J thc gauges are expensive.I\T,N DOOR

llost ovens with a flue above and outside the,, en doorway do not have a hinged metal.r )or or pair of doors to close off the mouth

ofthe oven itself, because they are not nec-essary. Hinged lightweight metal doors areoften fitted to ciose offthe outer opening ofthe chimney recess ofindoor ovens to ensureno smoke enters the house, to screen the oc-cupants fi'om the heat of the oven, and (insome counties) to meet fireplace codes. Ifthis kind of door is closed when the oven isfired, draft air must be available through theash slot or through draft slats or controls inthe doors themselves.

Instead ofhinged doors, most ovens havesimple metai or metal and r,vood doors u'ith aD-handle on the outer side. These are easilyplaced and removed as necessary) and they siton the lip between the ash slot and the oven

sheet metal*" plywood

arr spacealuminum foil

ash dump

hearth slab

Longitud.inal section throwgh tLn olev, door and. the outeroyen doorttay.

=1'I

i10'

top of arch

PREPARING TO BUILD A MASONRY OVEN 143

angle iron Alintel \ M-##atlI


16/28

Soapstoneis f,ne for

flntbreod., butwhy linoityowrself toflatbread.?

t44

door. This kind of door is used whenever theoven is used to bake loaves, and it is left outwhen pizza is baked with the fire pushed tothe back or side ofthe oven.The exception to this discussion aboutremovable doors is for small commercialbakeries, where it is more convenient to usecounterweighted doors that either fall awayin front of the peel or lift up out of t1le way(into the chimney recess) when activated bythe baker.ENCLOSUREA vented enclosure, preferably of masonryor metal, protects the outside of the ovenand its insulation. The minimum thicknessof the enclosure may be dictated by buildingcodes. The enclosure includes the facade ofthe oven, its outer sides, and its back and cap.Make an access and inspection door in the topof the rear of the enclosure .CAPMany ovens have a masonry cap that rests ontfe .n.lor.r.e walls and closes off the spacearound the oven dome. The cap is essentiallythe top of the oven structure. It is typicallymade ofreinforced concrete. Many other ov-ens are capped with sheet metal. Some arecapped with wood, but experience (and, inmost locations, the building code) indicatesthat is not a good idea.ROOFOutdoor oven enclosures are either roofedover with a separate roof, or the cap of theenclosure itself can be of some non-combus-tible material, pitched to shed rain. I favorseparate roofs, as they make the outside of

the dome more accessible. Because mostforms of heat-resistant insulation will staywet if exposed to water, and because stuccowill crack ifparts of the outside of a stuccoedstructure are heated to different tempera-tures, covering an entire oven with stuccorequires perfect detailing. I don't really fa-vor depending on stucco for waterproofing,because I live in a wet climate with largetemperature extremes. I favor a masonry cap(a thin, reinforced slab) that is completelvwatertight and can be removed if you needto modifi'your oven in the future.A stucco enclosure and roof combined.however, is something that lots of othershave done in drier and more temperate plac-es. If you want to try it, be sure to space thestucco mesh or plaster lath out a few inchesfrom the oven and the chimney, then caparound the chimney with metal or stone)creating a thermal and structural break.That wan the stucco will heat more evenly. Ifan entirely masonry oven enclosure is whatyou have in mind, consider a brick, slate,concrete, or stone roof, and you will.makeit watertight.CHIMNEY MATERIALSThe chimney recess is built of brick that istied to the brick or stone ofthe facade. Abovethe recess the chimney (for an indoor oven)must be lined with formed clay flus tiles orapproved metal flue pipe. Indoor ovens needa damper so that warm air from the room isnot drawn up the chimney when the oven isnot being fired or used for baking. Outdoorovens should have a chimney cap in rainy cli-mates, and a spark screen in dry ones.

THE BRI,AD BUILDERS

.:4z


17/28

l\u(zi7r1r , tll/ Itl,il

I45


18/28

Design choicesYou will be more familiar u'ith masonry ma-terials after ltou have read the chapter onmaterials (chapter 8). If ,vou are going tobuild your own oven, you need to buy abasic book on masonrv construction or getone from the library. It rn'ould be wasteful toduplicate all of that information here. Aftereducating yourself you must still make sev-eral decisions:1. Do you want a slab and block walls as

your foundation (as is presented in thisbook), or some other arrangement'such as a hear,y-duq'welded metalstandf2. Are you in a cold climate, where thefoundation should be insulated orplaced over a rubble footing to preventfrost heavingf

3. Do you want an ash slot in the hearthfThey are convenient for bread ovens

6..- but optional for pizza ovens, where thefire is pushed into the back or side, notraked out.4. \44rat is your comfortable workingheightf For most people it is a littlebelow elbow level. Remember that thisis the height of the finished hearth, notthe height of the ash-dump walls or theheight of the top of the hearth slab.The traditional height of a Europeanhearth is 90 centimeters-about 35r/zinches; however, manv bakers like ahigher hearth. A lower one will nzt do,unless children will be actively involvedwith the oven, as at a school.

5. Will you use firebrick or red brick forthe u-alls and domef If you use firebrick

for the walls and dome you need 10percent feu'er bricks than the standardplans call for, because firebrick arelarger than red brick.

6. Will you use Portland cement oralumina-based concrete for the hearthslab and cladding of the oven, and horvthick will the cladding bef Use aluminaand a thicker cladding if you are goingto be baking every dng or if you lvantto bake more than three loads Perfiring.7. Do you want thermocouples, and hou'manyl I recommend at least one in thewall or dome, and one in the hearth,but having a series of three of them inline somewhere in the dome is evenbetter.8. \A4eat will the facade of the oven looklikel

9. \44rat type of arch do you want at theopening of the chimne), recess, andwhat type of brick, stone) or tile is to beseen on the facadef

10. Do vou want a stone slab or bricks forvour outer hearthf

f 1 . Will you insulate dre bottom of thehearth slab to save heatl This will beworthrvhile if you plan to use the ovenmore than once a week, and it addslitde expense or labor.

12. How will you insulate the dome andwalls of the oven)

13. Ifoutdoors, what kind ofroofand en-closure do you wantf If indoors, whatkind of outer oven finish do you want:Brick, stucco, stonef

14. Will your flue run straight up, or doesit need to snake around somewhere toget out of the buildingf

-1-r

:

F+--_"

t46 THE BREAD BUILDERS


19/28

As you can see) there are many questionsthat must be answered-and this list is by nomeans complete. Building a masonry ovenrequires a certain amount of forethought,but remember, the more considerationyou devote in the planning stages the moresmoothly the construction processes will pro-ceed and the more satisfied you will be withthe final outcome.

Bwying nn O1)enAs this book is written I know of onlyone company making modular masonryovens designed primarily for baking loafbreads-Dietmeyer, Ward, and Stroud ofVashon Island, Washington, makes bothretained-heat and white modular ovens insmall, household sizes-but beginning inthe early I980s, several companies began to

147

Brickworh tet'ms.

PREPARING TO BUILD A MASONRY OVEN


20/28

import or manufacture multipurpose ovensdesigned primariil, for baking flatbreadsand for roasting, but usable for loaf breads.Some have domes of refractory concrete,some of high-fired refractory clay. Somehave hearths of dense, nonporous high-fired cla-v. and some use less dense ceramicsformulated specifically for hearths. Pleasesee the Sources list for contact informationfor these suppliers.If you are considering purchasing a man-ufactured, modular masonry oven, and planto bake loaves, keep these important charac-teristics in mind:1. The masonry of a retained-heat oven

should be at least four inches thick toguarantee that enough heat can bestored for trvo bakes without refiring.2. The hearth material should have a den-sity and conductivity not greater thanmedium density firebrick (130 pounds

&

per cubic foot, and B .5 btu x in/hr x ftsquared x degree Fahrenheit or, in met-ric units 2.06 g/cm squared and 1.23W/mx degree C.)

3. Get one that has been approved by anational testing agency. Otheru.ise youma,v have problems u,.ith the local codeofficers, since the wall of the oven is go-ing to be less than 8 inches thick.Some suppliers furnish ovens in parts that

require assembll', but that are easily carriedto the site. Some supply prefabricated ovensthat don't require assembly but may need aforklift or a lot of ingenuity to unload andinstall. Some ovens can be orderedwith metalbases that are lighter than concrete block;these may, be installed on an existing floor.Some suppliers don't have much to offer inhousehold sizes. Some supply oven tools aspart of the kit. Make your selections carefullyto be sure you get what will work for you.

r48 THE BREAD BUILDERS


21/28

VISiT

MUGNAINIIMPORTS

Wotsontille, Colifurnin

l)orrtnr ovE\ Il.\r'RS were built in Devon, England, for hundreds ofI yents. erported. and rvidelv used in colonial houses in this counrr).ln other parts of Europe there is a similar rradirion of prefhbricared, I


22/28

VISITMUGNAINIIMPORTS rounded dome formed ofrebar, metal lath, and stucco, while the larger homeovens (the "Medio") usually get a roof and u'alls.

The domes of the Valoriani ovens are insulated with blankets of kaolin-based ceramic fiber insulation, then 6 inches of loose vermiculite. No attemptis made to insulate the hearth. n'hich sits on a site-br.rilt concrete and sardsandrvich that is fourreen itrches t-hick overall. The olerr dome is much thin-ner than thar of a site-built bread oletr, and so stores less heat. The modularovens are thus better and more efficient for cooking flatbreads, for roastingrvith a fire in place. or for cooldng one load of bread loar es. but they will notcook multiple loads of loaves without refiring'I visited Andrea at her California-Mediterranean hillside house, wth itshillside stone and terra-cotta terrace and su'eeping vicws of the central Cali-fornia coast. Talk about ltaly-I catne a\\-avwith a powerful impression ofthepotential for elegance that an outdoor oven offers in such a setting. It becomesa Iit-esq'le statement that Americatts can interpret. Andrea says, rhrough theirlong experience with barbecues and fireplaces. I also realized thal there areplenw of people who don't wa.nt to build their own oven. and there is noreason they should. Thel' 6an have someone else do it, and using a modularoren kit rvill probably lower the overall cost of professional installation. Onthe other hand, it was clear to me from my I'isit to Mugnaini and m1, revie$'of the catalogucs of the other companies in this business that a site-built ove ltrvill be better l'or loaf bread rhan anvthing thar is currcntly comme rciallv avail-able, because the masonry of site-built ovens is thicker.TECHNICAI POINTS. Although Andrea supplies thermometers that may be used in the ovens,

she advises he r customers to learn to iudge the hcat in the oven bv di-rect observation-for example, pizza edge s and toppings should bubblein thirty seconds and a plate-sized pizza should cook completely in threeminutes. This means that the oven temperature is betlveen 650 and 750degrees Fahrenheit (345 to 400 degrees Celsius). The desired 450 to500 degrecs Fahrenheit t230 to 290 degrees Celsius) oven lor roastingis maintaine d by obsen ing the cooking food, feeling the heat with ahand in the oveu, then adjusting the draft door. fire, and the exposureof the food to the fire. She recommends a cooler oven for loaf bread,

*,


23/28

.. i:;:.n::f.'t'.r'rl.::::;*

achie'n'ed by closing the oven for several hours (usuallv or.'ernight) after ithas been used lbr other cooking.. -{ndrea likes the nonporous hearth tiles, in preference to more porousfirebrick, because she does a lot of roasting, and liquid spatters ancl foododors don,r ger into the tiles. Also, the large size of the tiles combinesri'ith their high conductivigv to evenll' distribute heat in the hearth-hotspots are not a problem. of course, the dor,vnside is the relative deli-cac.v (to thermal and mechanical shock) and rapid heat transfer rate ofrhe tiles, u,hich theoretically could be a problem r.vhen she bakes loavesinstead of flatbreads. Since she usually rvaits until the next day to bakebread and the ovens have tro lrearth irlsulation. it mr1'be that she aloidsburning the bottorn of her loaves because the hearth becomes slighdvcooler than the dome.

Tbis Mwgnaini wodwlarown is pat"t of a nearl,t,co?npleted house inCaffirnia (photo:Mugnoini Iwports).


24/28

\.TSTTMUCNAINI

IMPORTS Andrea was arranging a regional distribution sysrem for the ovenswhen lye met) and may in the future be able to make referrals to localdistributors and/or installers. Up to norn. she has shippcd everythingfrom warehouses in Watsonville and Los Angeles, though she has anew office h Nerv York.Although it is environmentally appropriate and economically soundto use locally available materials and labor when possible (which iscertainlv possible when ovens are built of uarive.lry. o. of bricksmade from native clay, or of a refractorv mixrure of alumina cementand heat-rcsistant nrtivc rock). nor e\er)'part of the U.S. has goodclal', a local brick kiln, or a source of heat-resistant rock. The scratchmaterials you bu,v ma,v have been trucked two thousand miles, whilea prelbbricated European oven r,vill have been shipped ro rhis counrr\rby water, a relatively efficient method, and trucked a feu' hundredmilcs.

n-

RJ+,


25/28

VISITSAN JUANBAKERY

San Juow Bautistn,LalUorntlz

HOMEFIRESBAIRYLe nt e nw or th, Wash ingt o n

The soard,ougltsta,Trter end

soard.ough brendrecipry.re

wnchonged'inf,fty yenrs

or ALL BRICIi ovENS r,vere made to be fired rvith rvood-coal-firedovens are still common in Neu York Cin, and large oil or gas orerrs

rvere built in many areas into the 1950s and some gas-fired masonry ovensare being built today. Let's look at two such ovens, one directly-fired (aburner pointed into the mouth o1'thc ovcn ) and onc externallv-fired rwirha burner in a separate fire box r,r'ith its own fuses).

There is an carll gas overl in the srnall missioll to\\'n ol'San JuanBautista, California, r,vhere in l93B Reno Cornaggio got tired of therecurrent flooding in his oven room and bought the building across thestreet. He hired Paul Metz, a u'ell-knou'n oven builder from Oaldand,to build a large gas fired brick or.en-its inside dimensions are about 12x 12 feet. It has been in continuous usc sincc it u,as built, b), Cornaggio(rvho often sang opera in the street), b), Bill and Gladts Paradis (u'hobaked everl'bod\t's turkey, al1 of them at once) at Thanksgiving), and fbrtl-re past sixteen years, b1, John House, no\l'in his mid-sixties. The sour-dough starter and sourdough bread recipe are unchanged in fift1, ygn15,the recipe for Portuguese orange nut bread r'vas acquired by Bill Paradisbefore he bought the bakery, and the horizontal paddle mixer, the slicer,and tl-re oven are unchanged.

The orren's heat storage is immense, as the hearth bricks rest on 13inches of sand and the dome bricks are covered with the same amount. Theoven is fued for two and one-quarter hours at the end of the afternooneach da,v so the heat can equalize b)'morning. On Sundal. (his biggestbaking day), ]ohn bakes trvo hundred and fortt,)'easted French loave s, trvohundred sourdough loaves, and any number ofloaves ofherb and onion,garlic Romano, pesto tomato, cheese and jalapeio) potato) and Portugueseorange nut breads, in addition to pastries and cookies. Hundreds andhundreds of loaves on one firing of tl-re oven-the massive heat srorage ofthis oven does the trick.There is a verlr different gas-fired oven I teu' miles outside theB avarian/Tyrolean-theme tor.vn of Leaven\rorth, Washin gton : a "lvhite"or externally-fired and vented masonrv oven, built in 1985 bv Dietmeyer,Ward, and Stroud, of Vashon Island, Washington, under the guidance ofErnst Heuft, a fifth-generation German sto\re mason r.vho lives in BritishColumbia. The style and the rvorkings of this oven are q,pical of small


26/28

VIS iT

SAN JUAN BAKERYand"

HOMEFIRESBAIRY

commercial masonrv ovens in Germanl', Austria, and Switzerland, and manyof the oven parts lvere imported from Europe. Although built for lvood-firing. it was converted to propane seven )'ears agoi ir can be converred backto q'ood-firing in a matter of minutes, should that ever be necessarr,.The eificienc.v of external-firing commercial or.ens mav justifi' their com-plexiry since the puryose of any firing schedule for a masonry oven is to heatthe outer part of the mass to a temperatltre abol'e that required b)r the bak-ing bread. That wa1, heat r.rill florv into rhe oven as breacl is baked, uithoutol'er-heating the bread early fu the baking cycle. With a directly-fued oven,this is achieved by carefully timing the firing, clean-out, resting, and bakingoperations. There is little recourse if the oven is rlor hot enough when youwant to use ir, or ifyou want to bake extra loads. with externally fired ovens,however, the hear is alv.a)rs coming into the oven from outside (u'here it isgenerated), and continuous or intermittent firing can provide heat at therate it is used, while retaining the hearth conducrion, radiant hear. and highmoisture advantages intrinsic to masonr)' o\ ells.

What is the dou,nsid.ef Cost and complexit\.. The HomeFires oven cosrabout $15,000 in 1985, and that rvas abour $5,000 ior,r'er than it otherwiseu,'ould have heen because the constructors wanted to gain experience withthe techniques used to make it. with inflation and currency changes (for thesame imported castings), the same oven r,vould cost about $50,000 in \997dollars, which is a lot to pa1, for an oven that has half or a third the hearthspace ofan equalll expensive deck oven.

\44rat is the oven likei It is a large rectangular masonry structure q'ith abrick front and stuccoed sides. In its face there is an iron oven door that slidesuprvard on iron tracks, its u'eight counterbalanced by iron r,veights on the endofrwo chains that run from the upper corners ofthe door over two toothedidler sprockets, then down to tlvo iron tveights. There is no outer hearth,but there is an inner transitio' hearth of smooth stone that slopes sharplvLrp to a gradually sloping oven floor of refractorv blocks. At rhe far cornersof the oven there are smail cooling venrs. controlled b)' big chrome-plateddamper handles on the ftronr face of the oven, while on the right inner ovenwall there is a small opening in the bricl< oren lining to let irr sream. Sreanris gcnerated by allowing \\-arer to run into a copper funnel mounted on thestucco wall. From there it runs to a thick-r,ralled metal box on the side of the

$.6rtatlbuionstarTh,andllltdt,ilitthebaclcal icotl1

the ;


27/28

John Howsa nt tbe Snn JwanBaker.v. Tfu pipes brhintl hiwserve thc gas burnerantl the ttea.nz injectal Therigid gas pipe is joinred, andcan swing into the rnouth&s the u)en is f'red. See howhigh this hearth is? The dooris cou ntrr-weighted (phon,:Dina Dabois).

firebox, wheie it instantly boils, releasing steam into the oven. Because this isan open sysrem gr both ends there is no risk of steam explosion, and if scalehuilds up it is easTly removed.

The fire box is under the rear of the oven, with an iron door that openson thc righr side of the oven base. Dampers direct rhe flame into vertical (forirarting the fire, or to reduce heating of the hearth)or horizontal channels.The firstpair of horizontal channels run the full length of the ov1n, undeland on each side of the center line of the hearth; they then double back, stillunder the hearth but under its ourer aspect. They end in vertical tubes thattake the smoke above the oven and empt.v it into horizontal channels over-,Jre outer aspect of the oven roof; these take it forward, so that ir can be sentback again in rwo ( more centralh' located ) channels rhat finally join at I l..tricai tube that dumps into a last horizontal channel. At its forward end this is;ontrolled by the main draft damper. A{ter the smoke passes this damper itrcaches rhe chimneyl a flap-rype barometric drafr there automadcally adjustslhe force of the draft as the oven is fired. In all, the smoke makes five passes


28/28

\/ISIT

SAN JUAN BAIGRYenn

HOMEFIRESBAIRY

across dre oven brickwork, transferring heat to the masonry. Trvo internaldampers control the firebox, nvo control the cooling vents, and rhere isone main smoke damper and one barometric damper. There is a cleanourdoor at each 1SO-dcgree bend of the smol

preparing to build a masonry oven

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