The keystone brick or "key brick" is the final brick placed when building an arch of any kind. It is probably the most important part of an arch, and a dislodged or failing keystone brick can cause major issues, and even arch collapse!
For our hybrid Noborigama, we cut some special key bricks for the sprung arch in the front chamber, and poured castable refractory cement (often just called "Castable") at the top of the catenary arch in the back chamber.
The sprung arch key bricks had to be carefully cut and then set a little above where they needed to be, so they could all be hammered in together — thereby preventing any bricks from going too far down and letting one fall through the gap!
For the back chamber's catenary arch, we attached two small plywood boards to each end, and laid refractory castable in the gap. Once the plywood came off, we had a perfectly set keystone brick (visible as the darker color in the picture below). Ta Da!
KU students pouring refractory castable where the keystone for the catenary arch will be.
The next step was to weld some stabilizing metal framework around both arches before the plywood arch forms could come out, for extra precaution and to make sure that the arches themselves don't slump over time.
Zeynep Uner is the current kiln and wheel repair apprentice at Bracker’s, working directly with David Sturm (the head tech) on repairs large and small. She has been repairing kilns for approximately 3 years now, and has been absorbing everything she possibly can from David’s 30+ years in the field.
Zeynep enjoys atmospheric firing, taking film photos, and throwing on her old Brent kick wheel.
