Floor insulation

[david s]

The powdered clay in the dry 50/50 clay sand mix fills in the gaps between the grains of sand. This reduces movement of the sand when the floor bricks expand and contract with their heating and cooling. The mix is better if it’s dry because a wet mix will set up hard and make any possible removal of floor bricks to be replaced if required, extremely difficult. If you have difficulty sourcing bricklayers clay from bricklayers’ suppliers try pottery suppliers and look for Ball Clay or powdered casting clay.

[RickH]

I poured the perlcrete, came out pretty good, I was afraid that I did not use enough water, it was pretty crumbly but set up nice. I was able to find a bag of fire clay and I did a 50/50 mix with sand to set my floor. with help from my friends we were able to get it pretty level (and it passed the peel test with no snags)

My next question is with the indispensable tool, I made it with a castor, and I have the 21" radius at the bottom but when I go straight up I am 22" from the base of the castor, add another 1.5" for the thickness of the wood on the bottom , my ceiling will be at 23.5", will this affect my build?

Thank you

[UtahBeehiver]

The increase the dome height due to the pivot point off the floor level will not affect the operation of the oven. But with the pivot point off the floor level and the offset of the castor will affect the angle of the interior of the brick face. It will not be perpendicular to the center of the floor, the error is cumulative as you go up in courses and you will see a stepping of the brick face and the higher you go the worse it gets. It is also important to have the IT adjustable in length to adjust for brick variables. Also the line from the center of the dome along the IT NEEDS to intersect the center of the brick face. Right not the IT hits the top of the brick.

[david s]

The pivot point can be lowered to floor level by removing the centre brick and replacing it with a wooden brick of the same dimensions..When the dome has been built and the IT removed, the original brick can be replaced.

[rsandler]

To adjust your existing IT as Utah suggests to make sure the pivot point intersects the midpoint of the brick, you could cut the long piece of wood where you've marked a line. This new cut surface is what will contact the brick. Then, glue/screw the smaller block on top of the long piece, extending over the top of the brick. Better still, put a a spacer even with the new cut surface to raise the top piece about 1/2". I'm assuming you're using 2.5" thick brick, so you want the pivot point to be 1.25" below where the arm hits the top of the brick. Currently you have it 3/4" above (assuming that's a 1.5" this piece lumber you're using as the arm), which is going to get the angles increasingly wrong as you go up.

Here's the IT from my second build--you can see how the pivot point is ~1.25" below where the top of the brick will hit, and in that pic I also had mocked up attaching the IT to a wood block below floor level, as Davis S suggests: