Insulating layer, a question.....

[carguy73]

I have attached a photo of my base, and I have been having some issues figuring out what I am going to use for my 4" insulation layer.

I originally wanted to use Plicast 16, but at $60 a bag, and needing 15 bags to fill that hole, I opted for a more economic solution! I have seen people talk about fire-clay mixes, perlite mixes, etc, and I am wondering what is the best to use?

Fire-clay mix = 1 bag fire-clay, 2 bags Portland cement, 6 bags sand.

Perlite mix = 6:1 perlite, Portland cement.

My question is this I guess:

Is it better to use a bag of fire-clay, 2 bags of cement, and 6 bags of perlite, or just the perlite/cement mix?

I want something that will A) last the test of time, and B) keep the heat from going through the structure.Any help, guidance, wisdom, would be MUCH appreciated!!

[RandyJ]

Why dot you consider useing ceramic board insulation under the oven. It is way more efficient than the vermicreete or something like that. It is a little expensive but not what you are talking about. I got mine from McGills warehouse. I thought that the price was pretty reasonable. I think 12 sqft 2" thick shipped to MN from CA was 100$ shipping included. I don't know where you are compared to them but maby you could save the 40$ a box in shipping to drive to them. I used 3 boxes to do the floor and part of another for a door. I have a 40" dome with 4" of insulation under it . That is what I would do.

Randy

[carguy73]

Not really the route I want to take, but I am open to persuasion. How does it lay, board with refractory cement cover? Tell me more....

[RandyJ]

The way I set mine was just flat on top of my stand. You don't need to mortar it down or anything else. It is 2 to 3 times as good a insulator as vermicreete. I used 4" on my oven sitting on patio stones to get the height I wanted. I put 3 " of ceramic blanket over the top and filled the rest of my enclosure with vermiculite, and have incredible heat retention. It is quick, easy, and very effective.

Randy

[RandyJ]

I was thinking and thought you also might have wondered how to set your bricks on the ceramic board. I used the fire clay and sand mix and add water to a peanut butter consistency. Then set and level the floor. The dome just sits around the floor. Make sure to leave a expansion joint like a piece of cardboard works great as a template.

Randy

[UtahBeehiver]

Nothing wrong with using p-crete but 4" of p-crete, at best, is only equal to 2" of CaSi board which IMHO is the bare minimum of floor insulation. It will work, but heat retention will not be as good as if you installed 3-4" of CaSi. If you go the p-crete route I would suggest 6" or more. I am not sure what the fire clay recipe buys you. I would just go perlite and Portland no richer than 6:1 but look at CaSi board seriously.