March/April 2005 • PotteryMaking Illustrated 1 O ne of the most difficult and important factors to consider when planning to build a kiln is the kiln’s "scale." The potential size of a kiln is thoroughly discussed, debated and pondered whenever a potter decides to build a kiln. Kurt Wild and I have tried to address some of the questions about scale that arise when designing and building kilns. Without question, the most important question to ask when considering the scale of a kiln is how many pots can you make in a specific amount of time? Just how heavy is your production? Be honest with yourself. Make sure that the kiln that you build fits your production schedule and accommodates the size of the pots that you make. Building a large kiln, and then agonizing over how to fill it with enough work in order to fire it on a reasonable schedule, is a waste of your time and energy. Many potters are exposed to large kilns in school or the gas kiln at the local art center. These are high-production kilns, used by many people, making hundreds of pots per month. In many cases, potters use these huge kilns as a model of what they should build. Since the plans are flexible, the "Minnesota Flat-Top Kiln" design by Nils Lou can be sized to fit almost any space or studio. We have built them as small as 10 cubic feet and as large as 60 cubic feet with a car system. A kiln of about 25 cubic feet is ideal for a home potter that has limited space. Keeping in mind that the flu size does not need to change and the burner system is constant in a large or small kiln, you can build a kiln to suit your situation. These kilns can be built to use natural or propane gas. A small gas kiln can use a limited amount of fuel and be as safe as electric firing—just a simple shed roof is all that is needed for cover in most situations. I have built several of these kilns in garages. Just keep in mind that a good amount of space is needed around any fuel kiln. As always, you need to observe some caution when building a kiln! Please check with your local building/zoning department and the fire department for area regulations before moving ahead with this project. It would also be prudent to contact your insurance carrier about your coverage. It is better to be prepared before you start, rather than making changes after you are finished. These plans are meant to be a basic guide to building the kiln. You can take these plans and modify them to fit the space and size of the area that you are planning to use. It is very simple math to change or modify these kilns. Since these plans are for the kiln we built for Kurt, we have provided a material’s list, and Kurt offers notes and suggestions gathered during the building process. Following the basic ideas of Nils Lou but being a bit creative will allow you to have a kiln that is "the perfect fit." We also suggest that you obtain a copy of "The Art of Firing" by Nils Lou. This book contains a wealth of information on building and firing kilns, especially the Minnesota Flat-Top. The Building Pr ocess The Foundation The site for building the kiln should be a flat, clear area with a compacted gravel base or a concrete slab. The base for the kiln and stack are constructed using a combination of 8-inch and 12-inch concrete block. This kiln has a layer of 8-inch block positioned so the holes in the block run horizontally to allow air to pass under the kiln. A layer of 12inch block with the holes in a vertical position is placed on the smaller block, overlapping the seams. Another layer of 8-inch block is placed on top of the 12-inch block in the same pattern as the bottom layer. (See Drawing 1) Once the concrete block is in place and level, place the expanded metal or cement board on top as the base for the kiln floor. The Floor The floor of the kiln and the stack consists of 3 layers of brick: First, a layer of hardbrick; second, a layer of softbrick (K 23); and third, another layer of hardbrick. The two layers of hardbrick can be laid in the same pattern, but the pattern of the Building a Small Flat-top Kiln By Mel Jacobson and Kurt Wild Make your dreams of having a fuel-fired kiln come true with these flexible plans
Transcript
March/April 2005 • PotteryMaking Illustrated 1
One of the most difficult andimportant factors to consider
when planning to build a kiln is thekiln’s "scale." The potential size of akiln is thoroughly discussed, debatedand pondered whenever a potterdecides to build a kiln. Kurt Wild andI have tried to address some of thequestions about scale that arise whendesigning and building kilns.
Without question, the mostimportant question to ask whenconsidering the scale of a kiln is howmany pots can you make in a specificamount of time? Just how heavy isyour production? Be honest withyourself. Make sure that the kiln thatyou build fits your productionschedule and accommodates the sizeof the pots that you make.
Building a large kiln, andthen agonizing over how to fill it withenough work in order to fire it on areasonable schedule, is a waste of yourtime and energy. Many potters areexposed to large kilns in school or thegas kiln at the local art center. Theseare high-production kilns, used bymany people, making hundreds ofpots per month. In many cases,potters use these huge kilns as a modelof what they should build.
Since the plans are flexible, the"Minnesota Flat-Top Kiln" design byNils Lou can be sized to fit almost anyspace or studio. We have built them assmall as 10 cubic feet and as large as 60cubic feet with a car system. A kiln ofabout 25 cubic feet is ideal for a homepotter that has limited space.
Keeping in mind that the flusize does not need to change and theburner system is constant in a large orsmall kiln, you can build a kiln to suityour situation. These kilns can bebuilt to use natural or propane gas. Asmall gas kiln can use a limitedamount of fuel and be as safe aselectric firing—just a simple shed roofis all that is needed for cover in mostsituations. I have built several of thesekilns in garages. Just keep in mind thata good amount of space is neededaround any fuel kiln.
As always, you need toobserve some caution when building akiln! Please check with your localbuilding/zoning department and thefire department for area regulationsbefore moving ahead with this project.It would also be prudent to contactyour insurance carrier about yourcoverage. It is better to be preparedbefore you start, rather than makingchanges after you are finished.
These plans are meant to be abasic guide to building the kiln. Youcan take these plans and modify themto fit the space and size of the areathat you are planning to use. It is verysimple math to change or modifythese kilns. Since these plans are forthe kiln we built for Kurt, we haveprovided a material’s list, and Kurtoffers notes and suggestions gatheredduring the building process.
Following the basic ideas ofNils Lou but being a bit creative willallow you to have a kiln that is "theperfect fit." We also suggest that you
obtain a copy of "The Art of Firing"by Nils Lou. This book contains awealth of information on building andfiring kilns, especially the MinnesotaFlat-Top.
The Building Process
The FoundationThe site for building the kiln
should be a flat, clear area with acompacted gravel base or a concreteslab. The base for the kiln and stackare constructed using a combinationof 8-inch and 12-inch concrete block.This kiln has a layer of 8-inch blockpositioned so the holes in the blockrun horizontally to allow air to passunder the kiln. A layer of 12inchblock with the holes in a verticalposition is placed on the smallerblock, overlapping the seams. Anotherlayer of 8-inch block is placed on topof the 12-inch block in the samepattern as the bottom layer. (SeeDrawing 1)
Once the concrete block is inplace and level, place the expandedmetal or cement board on top as thebase for the kiln floor.
The FloorThe floor of the kiln and the
stack consists of 3 layers of brick:First, a layer of hardbrick; second, alayer of softbrick (K 23); and third,another layer of hardbrick. The twolayers of hardbrick can be laid in thesame pattern, but the pattern of the
Building a Small Flat-top KilnBy Mel Jacobson and Kurt Wild
Make your dreams of having a fuel-fired kiln come true with these flexible plans
middle layer of softbrick should be changed so the joints are staggeredbetween layers. You should pay closeattention to maintaining a level, flatsurface with each layer of brick. Thisattention to detail will help ease theconstruction of the rest of the kiln.(See Drawing 2)
The WallsThe first course of the wall
is a soldier course. The bricks areplaced on edge so the layer is 41/2
inches high. You should start withthe back wall (See Drawing 3) toposition the flue (41/2 x 7 inches) andthe burner ports (41/2 x 41/2 inches).You will notice that the flue openingis just slightly off center on thedrawing to allow for use of a fullbrick on one side. This will not affectthe kiln’s operation. Continue withthe soldier course and allow for thedoor opening. These plans show thedoor on the front wall of the kiln(See Drawing 4) but in Kurt’s kiln thedoor was placed in the sidewall.Either option will work. Someinsulation bricks will need to betrimmed to size using a hacksaw or aregular handsaw.
Once the soldier course iscompleted, continue building thewalls. Rows 5 through 16 are laid inalternating courses (See Drawings 5and 6). When starting to place thebrick for row 5, you may need toadjust the brick on the back wall sothat there aren’t any joints above theflue or burner port openings. Be sureto maintain the proper width for thedoor opening as you build the walls.
You also need to build inpeepholes for viewing the cone packsand the inside of the kiln during firing.Some people have used a brick built intothe wall that projects into the chamberas a shelf for the cone packs. You do notneed to do this if you place your conepacks on the shelves with your work.
The RoofThe roof consists of
insulating firebrick stacked on end inmultiple rows and clamped together.The first step is to cut out a 3/4-inchplywood deck that is just slightlysmaller than the inside dimensions ofthe kiln chamber. Be sure to includethe opening left in the wall for thedoor. This piece is mounted in thekiln using 2x4 braces placed at aslight diagonal to allow for easyremoval when you are finishedbuilding the roof. Be sure to useplenty of braces around the perimeterand in the middle of the form. Thetop of the plywood should be slightlyhigher than the kiln walls to allowfor the thickness of the ceramic fiberplaced on top of the wall as a gasket.
Tip: Place a chalk line ontop of the plywood to mark thecenter of the kiln from front to back.This line will help keep the roofsquare while placing the brick on topof the plywood.
When placing the brick inposition, dip the top 2/3 of eachbrick in a very thin slip made up ofequal parts fireclay, common sandand water. This slip should be thickenough to lightly cover the brick’ssurface, not just stain it. Not coatingthe whole brick will prevent clayparticles from falling into the kilnduring the firing. The clay slip on theother part of the brick will help holdit in position when clamped togetherin the next step.
Set each brick in positionwith the clean end against theplywood. Work from the centerlineout to each edge starting at the frontof the kiln. Butt the bricks as securelyas possible, small gaps will disappearwhen the bricks are clamped together.You do not need to dip the bricks thatrest on the wall into the clay slurry.Place the three hard firebricks on eachcorner as shown (See drawing 7).
Tip: Although you canperform most of the constructionprocess as an individual, it is a wisedecision to enlist help from others forseveral of these steps, especially whenbuilding the roof.
You are now ready to placethe corner braces and tie rods inplace. Make the four corner bracesby welding pieces of 21/2 x 21/2 x1/4-inch steel angle together and drillingholes in the appropriate locations.(See inset on drawing 7) Position thebraces, add the tie rods, nuts andwashers, and snug them up evenly.Place hard firebrick splits betweenthe brick and the tie rods on eachside of the roof (See drawing 7)before tightening the nuts on the tierods. This will keep the bricks frombowing out or the tie rods frombowing in during the tighteningprocess.
Once you have applied aslight tension to the roof structure,remove the middle inside support.Replace this support with a shorterone and a hydraulic jack. Raise thecenter of the roof about 3/4 inch tocause a slight domed effect. Continuetightening the tie rods in an equalmanner working from front to backand side to side in several steps. Atorque wrench is recommended andyou should tighten to about 40 ft/lbsof torque. The roof is now a slightlydomed, solid slab. Once you fire thekiln, you will want to re-tighten thenuts to 40 ft/lbs to allow for anystretching of the metal tie rods orshrinking of the brick.
Tip: It is a recommendedpractice to check the tension of the tie rods after several firingsthroughout the kiln’s life.
Corner BracesYou can now add the
bracing for the corners of the kilnstructure. This consists of a 2x2x1/4
2 PotteryMaking Illustrated • March/April 2005
inch thick angle iron that isapproximately 76 inches in length oneach corner joined by tie rod orcable. A unique feature on Kurt’s kilnis the use of 1/8 inch steel cable andeyebolts to join the corners together.The eyebolts are placed in holesdrilled through the angle iron. Theholes are drilled so that the top holesare 2 inches above the roof and thebottom holes are 4 inches below thehard brick floor. One end of thecable is looped through the eyeboltand fastened with a cable clamp. Theother end is passed through theopposite eyebolt, pulled tight andfastened with a cable clamp. Whenall 8 cables are in position, slowlyand alternately tighten the nuts onthe eyebolts to create an even tensionon all the cables.
The Flue Box and Chimney StackThe flue box is designed to
create a double Venturi effect on thegases coming from the kiln chamber.This system of restricting, thenexpanding, then restricting andexpanding again is used to create astrong draft of the flue gases andturbulence within the kiln chamber.
The flue box uses acombination of hard brick laid flatand soldiered to make the 1-inch slotfor the damper (see drawing 8). Thedamper is made from a 1-inch thickpiece of Kaowool "M" board. Thetop of the flue box is the second areaof restriction before entering thechimney stack. This opening is thesame size as the opening from theback wall of the kiln into the fluebox.
The chimney stack iscomposed of 10 inch inside diametergalvanized pipe and Kaowool sleevesapproximately 93/4 inch in diameter.These will slide into the metal pipeproviding you with a ceramic fiberchimney. The chimney stack should
sit on a piece of the ceramic fiberboard or blanket to provide anairtight seal against the brick of theflue box.
The chimney on Kurt’s kilnis 10 feet in height. The height canvary to some degree without affectingthe firing of the kiln. If your kiln isgoing to be located inside, thechimney needs to extend through andbeyond the peak of the roof. It willbe supported and secured by the roofstructure. If the kiln is outside, youwill need to support the stack eitherby having a shed over the kiln orusing a guy wire system to hold thechimney in place.
BurnersThe burners for this kiln can
either be a high velocity propane ornatural gas with forced air. Yourburners should have the requiredsafety devices such as apilot/thermocouple safety shut offsystem and be installed to meet safetycodes in your area. The burners areplaced on either side of the chimneywith the flame entering the chamberagainst the inside of the wall. Targetbricks can be used to direct the flamewhere needed. These bricks can bemoved to fine tune the firing of thekiln.
Other NotesThe internal measurements
of Kurt’s kiln are 311/2 inches wide by36 inches deep by 341/2 inches highfor a total of 22.6 cubic feet.
The actual setting space, using 2 12x24-inch shelves side by side set2 inches off the floor, is 10.8 cubicfeet.
Facing into the kiln, the shelves areset so that they are 4 inches from theleft wall and 2 1/2 inches from theright wall with the flue opening. The
shelves are placed so there is a 6-inchspace on both the back and front sideof the shelves to act as the flamewaysfor the burners.
Materials list for Kurt Wild’s versionof the Minnesota Flat-Top Kiln:
51 Standard 8-inch cement blocks (71/2 x 71/2 x 151/2 inches)12 12-inch cement blocks (71/2 x 111/2 x 151/2 inches)3 4-inch cement blocks (71/2 x 31/2 x 151/2 inches)
Expanded metal or cement board asthe first layer over the cement blockand before laying the brick. For thekiln proper, 1 48x54 inch piece or 224x54 inch pieces are required. Thestack base requires 1 18x18-inchpiece.
800 K23 insulating firebrick 9x4 1/2x2 1/2 inches (this amountincludes about 20 extra bricks tocover breakage and or cutting).
220 hard firebrick (straights) (9 x 41/2 x 21/2 inches) 8 #2 split hard firebrick (9 x 41/2 x 2 inches) 2 #1 split hard firebrick (91/2 x41/2 x 11/2 inches)2 1 1/4-inch split hard firebrick (9 x 6 x 11/4 inches) 4 thin split hard firebrick (9 x 41/2 x 1 inches) 1 21/2 x 41/2x12-inch or 121/2-inch hard firebrick (for over damper slot)
12x24-inch shelves as desiredShelf supports as desired
1 piece of Kaowool 48x54 inches or2 pieces 24x54 inches(optional/desirable added insulationover top of kiln)"M" board for damper and base ofmetal stack sleeve
March/April 2005 • PotteryMaking Illustrated 3
10 12-inch Kaowool sleeves (81/2 inch ID x12 inch length; 91/2 inch OD), to line galvanizedmetal stack2 5-foot-long sections of heavygalvanized pipe for stack (to be linedwith the Kaowool sleeves). Usingstandard 2-foot lengths of galvanizedpipe is not recommended, as theKaowool sleeves do not readily slidedown the pipe. Any heating andsheet metal shop can fabricate 5-footlengths. Be sure to provide the shopwith a Kaowool liner to ensure adecent fit.
1 72-inch piece of 2x2x1/4-inchangle iron is required for fabricationof the 4 roof corner braces.
1/2-inch cold rolled rod is required toconnect the roof corner braces:4 52-inch long pieces are required forthe sides4 45-inch-long pieces are required forthe front and back (each rod must bethreaded 3 inches on each end).16 1/2-inch nuts are required and 161/2-inch washers.
4 Corner, upright angle iron braces(2x2x1/4 inch) 76 inches in length.1/8-inch steel cable to fasten uprightbraces (you may want to have thecable cut to size at the hardwarestore as it is difficult to cut withoutproper tools). This kiln required 4pieces, 56 inches long and 4 pieces,48 inches long 16 5/16x4-inch eye bolts16 5/16-inch nuts16 5/16-inch washers16 cable clamps
