Sealing the Arch Bricks

What I have done here is put mortar on the edges of the arch on the inside (left photo) and the outside (right photo) of the kiln.

You can see on the inside - left photo - that the seams of the wall were also mortared. Even though there is an entire wall of soft brick behind the hard brick on the hot face - inside - of the kiln.

I'm not concerned about putting mortar between the arch bricks for 2 reasons. First is that the arch will expand and rise when it is heated during the firing of the kiln. If the bricks were mortared, it would hold back their expansion. The second reason is even more basic: There will be a layer of 2" of kaowool, the space-age insulation material, laying on top of the arch. The insulation will butt up against the stair-step of frontwall and back wall bricks that sandwich the arch together. In the right side photo you can see part of the stair-step of front wall bricks.

Kaowool is an excellent insulating material. It does have some natural forces that will detract from its insulating qualities as time passes. First is that kaowool does not like to get wet. Besides the kiln roof, I am going to great lengths to make sure the chimney opening will not leak any rainwater. Next, is that kaowool is a lofty product that loses some of its effectiveness when it is compressed. I will not place heavy objects on top of the arch & kaowool in the mistaken idea that it will increase insulation. The other natural hazards I have found to be much harder to fend off. They include birds pecking at the insulation for nest-building material. Other country varmits as mice, rats and bats will leave their scat on the top of the kiln - yucky! I have only found dead pencils in a kiln after a firing, but have heard stories of finding skeletons of lizards and even a cat (it crawled inside during a cold night, before the door was bricked up).