Brick by brick

[offcntr]

The big gas kiln at Club Mud had a problem. Concentrated heat in the fireboxes had baked the softbrick walls to the point where they were cracked, shrunken, or in worst case, curling like potato chips. Pieces were leaning out, blocking the flame path into the kiln, or threatening to fall out entirely. Obviously, something needed to be done.

I budgeted a week for kiln repairs. It took both more and less time than I expected.

I'd actually planned to tackle this earlier, working with Jon, the other potter who fires the kiln regularly. Then COVID set me back a week, and he volunteered to coach high school track in Portland and things got terribly complicated. Fortunately our treasurer, Don, had done a similar project on our previous small gas kiln, and he volunteered to help me out.

I did an estimate on brick needed--nine dozen--and ran up to Hi-Temp in Portland to collect them, just before my quarantine. Now it was time to take the beast apart. We took apart the bag walls--hard brick walls that take the burner flame and deflect it up into the top of the kiln--placing the two sides separately on the kiln car so we'd be able to reassemble them again later. Then it was time to attack the problem.

The walls of the kiln are two bricks deep. Most of the courses are stretchers--laid flat, running parallel to the wall, joins staggered. Every five or six courses, though we had headers--brick laid the short way, running through the wall, tying the inner and outer layers together. Replacing the stretchers was easy. Replacing the headers was like some reverse Jenga: tap the old brick out with a hammer and piece of two-by-four, slide in the new piece, all the while hoping the whole stack doesn't collapse. Then there were complications: the fully-loaded kiln furniture shelf that blocked the first three headers on one side, bricks too tight to shift on the other. We wound up cutting bricks flush and piecing in bits to fill awkward spots. Fortunately, Don is very good at cutting softbrick. I'm not; the saw tends to wander when I try.

It only took us three hours on Monday to do the entire right wall; another three on Tuesday for the left. (We could probably have continued working Monday--it was only 1 pm--but decided tired and stupid wasn't a good idea. I'm glad--the left side was the one with the too-tight bricks. I'm glad we came at it fresh.

Wednesday was a day off--Don had a standing appointment, and we were waiting the the ITC to arrive.

ITC 100 is a high-temperature kiln coating that reflects heat away from the surface it's on. It's amazing stuff--I saw someone make a firebox door for a wood kiln by slathering the stuff on a sheet of plywood. Coating our brick will help prevent it from overheating, cracking and shrinking again. It took two pints, diluted with 50% water (to make three pints total) to cover the entire new firebox surface, with a quarter cup left over.

I did it on Thursday in about an hour, then spent another hour with the shop vac, cleaning up scraps and brick dust. Friday, after everything had dried, I put the bag walls back together, did a little last clean-up, and put the extra bricks away. I'd overestimated, had three dozen left, but there's always need for repairs.