Floor: Firebrick and Insulation

[Travelinman]

Quick questions:

1) The order of flooring: I was going to put 4" firebrick, 2"ceramic insulated board, 2 1/2" of vermicrete, 3/8 porcelain tiles (cracked for drainage). Does this sound like the correct items and order?
2) Does anyone use NSA approved firebrick or is that just overkill.

Thanks,

Chris

[fox]

Sounds ok but it would be a lot easier to use 3-4’’ of ceramic fibre board forget the Vcreet and put some drainage holes around and below the board.
2’’ of ceramic board will work but you will still get quite a bit of heat transfer into the concrete support base, even 3’’ will allow the concrete to get pretty warm but if the underside is used as a wood store then that is not a bad thing.
ceramic fibre board will soak up moister and make it totally infective while wet but water will not destroy the board however the best bet is to put a lot of thought and effort into avoiding water Ingres !

[UtahBeehiver]

Are you laying the brick on edge (ie 4" thick) or flat (2.5" thick?) 4"thick floor is typically used for heavy duty baking due to the large amount of thermal mass to heat up. Using all CaSi is definitely the most efficient if your budget can handle it but CaSi/Vcrete (5 to 1 ratio) is a viable option so is all vcrete (but need to be at least a min of 4:" thick with 6-8" better. It is all budget and labor based.

[Travelinman]

Thanks Utah and Fox:

I have these massive bricks that were ordered about 80 years ago for a local lime kiln, which are 4" thick.

I will try the vermicrete at 4" with the 2" of ceramic board.

I am a little concerned about the weight of the whole brick dome on 2" of rigid form around the perimeter. Will it support the dome? The insulation was recommended on the forum.

Thanks, again.

[fox]

That is a valid concern, all I can say is the ceramic fibre I use is very dense and extremely crush resistant however I have noticed on some of my builds that the oven may sink a fraction (1-2 mm) over the first few weeks but not move there after. I assume there is some moister that drys out allowing a tiny movement.
what I do is allow 4’’ around the base so the dome is not sitting right on the edge, then the dome insulation will sit on top of the overhang.
i often see quotes on this forum about the cost of ceramic fibre board but where I live in the U.K. it must be considerably cheaper.
Re the thick bricks, the main issue will be heat up time and the amount of fuel to get it up to temperature...of course the bricks will hold onto that heat for a long time once they are saturated!

[Travelinman]

Thanks for your responses!

[Sandieego]

what about 4 inches of perlite and portland cement with a layer of aluminum foil below it to reflect the heat up?
so it would be 2.5 inches of fire brick, then 4 inches of perlite/portland and foil, then 4 inches of concrete.

[SableSprings]

what about 4 inches of perlite and portland cement with a layer of aluminum foil below it to reflect the heat up?
so it would be 2.5 inches of fire brick, then 4 inches of perlite/portland and foil, then 4 inches of concrete.

Welcome Sandieego. Adding a foil layer will not serve as a heat barrier and will prevent moisture from escaping. That's why we encourage weep holes in the hearth slab with loose tile sheets/pieces sandwiched between the slab and base insulation.

[Sandieego]

Thanks. I am pouring my slabs this weekend. was thinking of using a 2 by 4 for the perlite concrete insulating slab. as that is not 4 inches, I am curious if anyone feels that is sufficient insulation or should I add the ceramic 2" on top? from what i read the 2 inches on top would not be overkill as it allows better heat retention and probably easier to lay the firebricks?
Also, trying to see how people do these weep holes and not seeing much pre-pour except for doing pvc pipes placed about an inch below the suspended slab. I was thinking of placing a piece of toilet paper and stuff it with crushed rock, then allowing the concrete to crush it inwards making it part of the pour. Anyone think that reasonable? Or should I do two 1" PVC pipes?

[SableSprings]

Sandieego, you should start your own build thread instead of hijacking this one...helps all of us keep track of builds. Sorry for the short hijack TravelinMan.

As you have noted, a standard 2x4 will not give you a 4" layer of 5:1 perlcrete which is considered a minimum insulation base layer. I would recommend adding 1" or 2" of ceramic board on top of the perlcrete or just using 2" on the weep hole/tile slab top. Ceramic board is generally rated as twice as efficient as insulating concrete...so 4" of 5:1 perlcrete is roughly equivalent to 2" of ceramic board. The feeling by many on this forum is that extra insulation for any WFO is a good investment.

In answer to your weep hole question, you have two options. The first is to incorporate the weep holes in the slab pour and the second is to drill the holes after the pour has set (1/2" hole diameter is perfect). If you plan a drilling, then you need to take note of your rebar positions so you don't end up trying to drill through one (or three ). The easiest (IMHO) method is the pipe/tube embedding during the pour. Rigid 1/2" or 3/4" pvc pipe is set in the form so the top of the pipe is just slightly below the target top surface of the final concrete layer. Stuff the pipe top with some paper or cover with plastic wrap to keep the pour from filling the tube. Once the concrete is set and the lower form is removed, you take a piece of rebar and from below, pop out the top "thin concrete cap" of your pvc. This actually will form a small crater draining into the pvc...which is a good thing. I'm not sure that your toilet paper/crushed rock method will work as you do need to open it up and I think the wet concrete will most likely push through the paper and seal off your intended drain. If you can't get pvc, making a bundle of plastic straws should work. You should be looking at creating 3-4 weep holes underneath the intended location of your actual WFO structure. You will also want to cover the bottom of the weep holes with screen to keep "critters" from occupying them.

Hope that helps...and please start a thread so you can post pictures and we can more easily help you.