Ceramic Fiber Blanket under Hearth Bricks

[Priest777]

Hi all, I have a ton of ceramic fiber blankets left over and have used around 2” of vermicrete under the hearth bricks so far. Rather than using FB ceramic board I am wondering, “Is it possible to use 1” or 2” of ceramic fiber blanketing directly under the hearth bricks for extra insulation?

the reason is I have tons of blanketing and would rather use it than spend another $100 on the fiber board. Despite the compression of the blanket reducing the insulation, would this work in place of the Fb Board in concert with the vermicrete?

These forums are hugely helpful, thank you all!

[Mongo]

No, do not use blanket under your floor. Too soft, even once compressed. You want a rigid material.

[UtahBeehiver]

Mongo is correct. Floor insulation should be at least 75 psi at 5% compression.

[Priest777]

Thank you both for the advice! Per your advice, I have kept to the vermicrete / perlcrete insulating base with the hearth bricks laid directly on it. I have insulated the dome with 3” of ceramic fiber blanket to compensate.

thank you for the quick replies!

[UtahBeehiver]

Have you laid the floor yet? 2" of vcrete is not sufficient under the floor. You need at min of 4" at 5 to 1 ratio.