Ca-si board vs vermiculite board.

[mrotter]

Hello guys, I have two options for hearth insulation:

1. ca-si board - 40 mm thick
2. vermiculite board - 25 mm thick

Fairly similar prices. Would single layer of 40 mm ca-si boards under firebrick floor be enough?

[fox]

Vermiculite board is not suitable as it is very prone to cracking in larger pieces, the overall product is very brittle and it will suck up water like a sponge.
Not to say it is a bad product and it has many uses but it has very little structural integrity especially as a base supporting such a heavy weight.
The board is made from compressed vermiculite and water glass although the actual formular seem to be a secrete!
What many folk use is a mix of loose vermiculite mixed with cement as that forms a more stable and stronger result .
However the Ca si board is a popular choice as is ceramic fibre board .

[mrotter]

Vermiculite board is not suitable as it is very prone to cracking in larger pieces, the overall product is very brittle and it will suck up water like a sponge.
Not to say it is a bad product and it has many uses but it has very little structural integrity especially as a base supporting such a heavy weight.

I see, that is the exact information I need. So CaSi boards are de-facto standard material for this? Or should I look into some alternative insulating boards which can sustain such a weight laying on it?

[mrotter]

Also, I found premade Keramzit/concrete (Liapor - perlite-like insulant) boards.

[fox]

calcium silicate is a popular choice it is strong enough at around 100 tons per square meter and can withstand 1000 °C .

foam glass is also becoming very popular, I have never used it but it is so not prone to water damage.

Ceramic fibre has the best thermal properties and is what I use.

The most important aspect is to make sure you base insulation does not absorb water.

[mrotter]

Thanks! Will got with CaSi board or ceramic/foamglass board if CaSi will not be available.

[UtahBeehiver]

A couple other options, AiSi board will work as well, similar to CaSi. Here are a couple key components in addition to a high temp rating, 70-75 psia compression at 5% compression and a K value of about 0.55 Btu-in/(hr*ft2*F) at 500 F. If budget is a factor, a 5 to 1 p/vcrete is an option you just need twice the thickness of CaSi or AiSi. Min recommended floor thickness for CaSi or AiSi is 50mm. FoamGlas is a good first layer since it will not absorb water but it is hard to find. There are new perlite based boards with good thermal/structural properties and water resistance but I have not used them.