Floor insulation - many layers better?

[Frenchie]

Greetings all! My first thread here, I have to start by saying what a great community this is, full of knowledge and enthusiasm! Thanks for being here and I hope one day to contribute myself

In the meantime, my journey to build a 39” Pompeii dome oven is just beginning - with building materials. My local supplier is having supply issues with 2” fibreboard, and has instead offered 2x the qty in 1”. They have kindly given me the option of taking the 1” boards now for the same price or waiting until the 2” is available.

Apart from the slight hassle of cutting twice as many bits of fibreboard to shape, and staggering more joints, are there any downsides? Or indeed as the title suggests, is it even reasonable to expect marginally better insulation from several layers? Is it ok to separate the layers with foil?

Thanks in advance!

[SableSprings]

Welcome to the Forum Frenchie! Just to be clear, you are looking at a ceramic based board that will withstand high temps (~ 1,000F or 535C) and have a compression rating of at least 70psi. In the USA, fibreboard is not a high temp, insulation product...so I thought I'd better ask... A couple layers of 1" CalSil board (to give you at least 2" total thickness) is considered the basic amount of insulation for a WFO. Many builders add more insulation by laying the CalSil on top of either FoamGlas or 5:1 insulated cement (either perlite, vermiculite, or a mix of the two with 1 part by volume cement). You won't get better insulation value having two layers with overlapped seams vs a single thick layer, but the difference is negligible. It's the total amount of insulation thickness that matters, not how many layers it takes to achieve that thickness.

Do not separate the layers of insulation with foil as it serves to block moisture transfer. (That was an old school method to accommodate expansion/contraction during the firing/cooling cycle of a WFO.) In addition, you will want to include a drainage/water barrier between the concrete stand and the insulation base material...this is covered in several threads, so let us know if you can't find those posts & we'll direct you.

Good luck and we're all looking forward to your progress & build...

[david s]

Greetings all! My first thread here, I have to start by saying what a great community this is, full of knowledge and enthusiasm! Thanks for being here and I hope one day to contribute myself

In the meantime, my journey to build a 39” Pompeii dome oven is just beginning - with building materials. My local supplier is having supply issues with 2” fibreboard, and has instead offered 2x the qty in 1”. They have kindly given me the option of taking the 1” boards now for the same price or waiting until the 2” is available.

Apart from the slight hassle of cutting twice as many bits of fibreboard to shape, and staggering more joints, are there any downsides? Or indeed as the title suggests, is it even reasonable to expect marginally better insulation from several layers? Is it ok to separate the layers with foil?

Thanks in advance!

Layering the insulation boards will give you the same result as a single thickness. Foil between the layers will theoretically improve the insulation value, but it does also act as a barrier for moisture making water removal slower. Perforating the foil helps to allow moisture to pass. As long as foil is not placed against a conductive material it will work well to reflect radiant heat.

[Harrypopsom]

Do I need a special thermal concrete for a floor of an extension. Where can I buy it

[SableSprings]

Welcome to the forum Harry. No special type of concrete needed if you're referring to an area outside the heating/cooking area. Insulation separates cooking floor refractory casting or firebricks from a supporting concrete hearth because concrete will degrade at WFO normal firing temps.

Sorry to highjack your thread Frenchie.