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STORY AND PHOTOS BY JOYCE MICHAUD

Tree trunks rose 12 feet intothe air, supporting the corru-gated metal roof over a grav-

el-filled trench as potters arrived towork with Svend Bayer to build #9, aThai-style wood-fire kiln. The 180-cubic-foot, single-chamber kiln, builtduring a workshop for Hood College atMt. Hope Pottery, is the ninth wood-fire kiln built by Svend Bayer — andthe fourth which he has built here inthe United States.

The kiln foundation had been dugbelow the frost line and filled with 12inches of gravel and 4 inches of sand.The final 9 inches of pure silica sandfor the floor of the kiln would comelater, after all construction was com-pleted. The sand and gravel founda-tion and sub-flooring were smoothedand leveled side-to-side with a gradual

Top left: Foundation of kiln and firebox.

Middle left: Arch formers being installed.

Top right: Arch formers with lath attached.

Bottom left: Foot mixing technique.

Bottom right: Insulating layer of clay is applied.

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one-foot rise from firebox to chimney.

The sunken preheat firebox, whichlengthens the height of the door andallows walk-in access during loading,was adjusted. The cement foundationfor the chimney had been poured.

The kiln shed, built with indige-nous timbers, would protect the func-tional sculpture emerging on site overthe next seven days. Pallets of newbrick, clay and vermiculite, mounds ofsand and gravel, stacks of lumber, usedbrick, and firewood crowded the yard.

The footprint of the kiln emergedas the 9-inch-high brick foundation waslaid. By hanging a chain at the widthand height indicated on Bayer’s graphand making allowances for lumbersize, the catenary arches were marked,cut and assembled. Another crew mea-sured and marked the foundation andleveled bricks to support the arch form-ers at the proper height and positionevery 2 feet along the length of the kiln,and closer together in the downwardslope over the firebox.

The arch formers were set on theirtemporary foundations beginning atthe back of the kiln. Each arch formerwas perfectly centered and leveled inall directions before being anchored inplace. The top of the front arch formerwas angled back approximately 6 inch-es to finish the curve down over thefirebox. Tying the arch formers togetherby bracing with long lengths of woodcrisscrossed through the center open-ings created a stable, skeletal structureacross which the lath ribs would bestretched.

The lath spanned the arches to cre-ate a surface which defined the curvesand supported the weight of the bricks.The wood was thick enough to supportthe weight, but thin enough to curvewithout breaking. To facilitate the bend,thicker laths were scored on the insideof the area of greatest curve to about 1⁄3its depth. Cuts were closer together atthe sharpest area of the curve and far-ther apart at the shallow areas. Theconcave curve at the bottom of theslope just before the chimney requiredscoring on the outside. The lath wasfastened to the arch formers only asneeded for stability and to set thecurve.

The foundation bricks had beenlaid perpendicular to the axis of thekiln, giving a 9-inch base. The wall waslaid parallel to the axis of the kiln onthe inside edge of the foundation

courses, leaving the outside of thefoundation to support the clay, sand,and vermiculite insulation layer.

To facilitate straight edges of brickon the front and back of the kiln, a 2-inch-wide wood spacer, followed by ascrap piece of arch former, wasattached to the firebox and chimneyends of the kiln. Each layer of brickswas begun at both the firebox andchimney ends and met at different loca-

Chimney base former is leveled in place.

Parallel guide boards provide an end point for side bricks.

Gaps at top of arch are later filled with castable material.

Thai-style Wood Kilncontinued from page 43

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tions along the sides to provide foradditional strength of materials.

The bricks were laid with a clayand sand mortar (one bag of dry clay,six shovels of sand and three bucketsof water). The rows of brick movedparallel along the base of the kiln untilthe top of the curve of the flue wasreached. Keystone bricks were cut tofinish the arch over the flue. Brickscontinued to climb row by row aroundthe belly of the kiln.

Bayer calculated the placement ofthe four side stoke openings based onthe dimensions of the kiln shelves. Hepositioned the ceramic cylinders usedfor the spy holes halfway between theside stoke areas.

A measure was taken and parallellines were created as guides to definethe change in direction as the sidecourses ended and the bricks at theback of the kiln were laid in parallelcourses up the spine. The higher thecourses climbed, the more complex thecurves became until the rows of brickcame together in a zigzag pattern onthe top of the kiln. An elongated eye-shaped hole remained at the peak.

Anticipating the gaps in the brick-work, canvas had been stretched overthe lath to support the areas wherecastable refractory material would beused. The holes were cleaned of claymortar and the castable was mixedand pressed into the gaps in the brick-work.

As the brickwork progressed,crews back-filled dirt around the kilnto support the arch, laid a course ofbrick to support the 4-inch clay insula-tion layer that would cover the outsideof the kiln, and built the chimney. Theclay cladding made from equal partsof clay, sand, and vermiculite wasapplied in grapefruit-size balls, pound-ed to compress the clay, and then wastroweled to seal the clay and minimizecracking during drying.

A chipboard former, which wouldbe burned out later, was used to createthe chimney. This eliminated the needto measure and level, and allowedbricks to be stacked quickly withoutmortar. When the chimney, with itspassive damper, rose 12 feet into theair, angle iron was bolted on all fourcorners to its full height. The kiln shellwas complete.

The next morning, the arch form-

continued on page 46

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Thai-style Wood Kilncontinued from page 45

Top left: Bayer adds the last bits of clay cladding to the kiln.

Top right: Interior view of brickwork.

Bottom left: Stoke holes were smoothed and finished, the kiln complete.

Bottom right: Bayer surveys the first fire in the new kiln.

ers were disassembled and theinside of the bricks was exposed.The use of chipboard, a screwgun, and screws for constructionmade dismantling the complexgrid of braces and arch formers aquick process.

When the arch formers wereremoved, the door arch could befashioned and the front of thekiln finished. The kiln doorwould come later, with its threestoke holes: the preheat stokehole, the primary stoke hole(used to achieve intense flame

and heat rise), and the top stokehole (used to fill the firebox fromthe top, minimize the tempera-ture rise, and facilitate a reduc-tion atmosphere).

When the flames of the firstfire, set to burn the chimneyform, reached 6 feet, Bayerproudly reflected, “This is a gor-geous kiln! It is the best one Ihave ever made.” �

To learn more about this kilnbuilding project, go to the Web siteat: http://www.hood.edu.