First WFO build

[swarm1023]

Hey guys, I've been reading on this site for quite some time and have picked up a lot of valuable info, thanks.

I work at a ceramic tile manufacturer and have been given some kiln brick from a kiln that was taken out of service and am planning to build with it. The brick are 4x9 and have a 2.5" to 1.5" taper so they actually form the arch of the dome perfectly. I wandering however if it will take me forever to get that much mass fully saturated with heat, and also questioning putting fiberboard under the floor. Several here think the same way I do and that the fiberboard isn't going to hold up well over time being outside. Just the hot and cold and humidity will eventually break it down. So I'm thinking of just bedding it on a layer of crushed tile, which I think should hold the heat fairly well and since I will be standing the brick on its side I don't think too much heat will be going down through the 4" of brick.

I was in search of some hydrated lime and went to a local brick and block supplier that has been in business for many years and the guys there told me that they have never sold hydrated lime to mix in with the mortar. He said the Portland cement, fire clay and sand has never given them any problems, any thoughts?

I've got a little work into all ready, I'm building a retaining wall out of stone that I had laying around and will backfill with gravel and probably do a 6" layer of crushed tile to bed it on.

[swarm1023]

Re: First WFO build

Any and all suggestion/comments are appreciated, thanks

[david s]

Re: First WFO build

You need dense firebricks with thermal mass for a WFO. Your kiln bricks may be insulating fire bricks and therefore not suitable. Although insulating bricks are an excellent underfloor insulation as an alternative to fibre board.
Hydrated Lime is highly suitable as a binder for the temps seen in a WFO.

[mrchipster]

Re: First WFO build

Picture of your bricks would be helpful for comments.

[swarm1023]

Re: First WFO build

Yeah, these are very dense, heavy firebrick, not the lightweight, soft insulating bricks. Didn't think to get a close up pic of the brick this morning, but I have this. I done a quick layout when I was unloading the brick at the house just to see how they would stack up.

[mrchipster]

Re: First WFO build

Interesting shape, are you going to cut them in half and alternate row thicknesses?

1.5 inch row 1
1.75 row 2
1.5 row 3 etc..

[swarm1023]

Re: First WFO build

No, planning on leaving them full size. I'm afraid it will take longer to heat up, but on the flip side of that it should hold temp a lot better and longer.
I can get high heat clay for practically nothing so I'm going to fill the big gaps at the back side of the bricks with basically a high temp cob similar to what people use to make ovens with.

[Gulf]

Re: First WFO build

9" thick! Wow. Mexman, just tore an 8" one down and started over because of long heat up times . But, that is your choice.

[swarm1023]

Re: First WFO build

Well, that's kinda been my concern, didn't know if anybody else had had any issues trying to use a full size brick. I'm gonna have to think about this a little more.

[mrchipster]

Re: First WFO build

4.5 inch thick dome is a lot and 9 inch will take a long time to heat up and use significant amounts of wood. If you do decide to go the full 9 inches, how thick and what type of brick do you want to use on the floor?

I hope you have free wood available.

[swarm1023]

Re: First WFO build

I'm planning on stacking the brick for the floor, turning pieces in opposite directions to have a flat cooking surface.

Not exactly free wood, but there is a hickory mill here that will sell their left over pieces for $10 for a pickup truck load.

Starting to think I'll cut the brick in half.

[mrchipster]

Re: First WFO build

I know it might be hard to do but I would buy brick for the floor. The reduced thermal transfer and difficulty in getting a smooth floor using tapered bricks will make it well worth the extra money for proper floor bricks.

That is almost free wood and if it is kiln dried it is better than free.

[swarm1023]

Re: First WFO build

well my original thought was to stand the bricks on there sides, see pic, but I thought by stacking the brick it might actually help to insulate by allowing the bottom layer of bricks to act as an insulating layer.

yeah, the wood is kiln dried and works great, I've used a lot of it in my smoker.

[mrchipster]

Re: First WFO build

well my original thought was to stand the bricks on there sides, see pic, but I thought by stacking the brick it might actually help to insulate by allowing the bottom layer of bricks to act as an insulating layer.

yeah, the wood is kiln dried and works great, I've used a lot of it in my smoker.

Dense Firebrick is not an insulator and a 4 inch thick floor will be very difficult to get hot. But better than your layering idea.

The space between the two bricks will limit your transfer of heat from the top brick to the lower brick. the layered brick approach will give you the worst of both thin floor with minimal thermal mass and a heat sink that is taking heat away from your floor but not allowing efficient transfer of the heat back into the oven.

You will be wicking heat away and because of the minimal air space between the bricks you will waste significant energy getting the heat into and out of the lower bricks. The air gap acts as a thermal break but radiant heat will still be lost to the brick you will just loose a great deal of conductive heat.

In order of effectiveness as an insulator. Air is the biggest insulator in this analysis but only when not allowed to move thus the air trapped in the small cavities of the insulation.

Ceramic fiber
Foamglas
Insulating fire brick
Perlite
Vermiculite
Perlcrete or vermicrete
Sand/glass
Firebrick

[swarm1023]

Re: First WFO build

ok, more to think about.