Cement board (hardie backer) with water glass

[wileythenord]

Has anyone ever experimented with cement board coated with water glass to create a "batch box" for a rocket stove? These materials are very cheap and it seems to me if you place fire brick splits at the burn tunnel end of the chamber and just coat the rest with water glass it should be able to withstand prolonged use. 

I'm thinking about trying this, creating a box, coating the inside with fireglass, wrapping the outside with ceramic fiber blanket and then covering that with another layer of cement board for finishing. Any reason this wouldn't work?

Thanks,
Wileythenord

[josephcrawley]

Unfortunately portland cement based products start to breakdown around 300C. The cement board will absolutely exceed that in your design with or without the water glass.

[Deleted]

Dec 15, 2020 6:37:19 GMT -8 wileythenord said:

Any reason this wouldn't work?

The Achilles' heel of portland cement:

Ettringite Ca6Al2(SO4)3(OH)12·26H2O watercontent about 37%

Alternatively:

One could try to soak rock wool insulation or refractory calcium silicate board/blanket with a mixture of kaolin clay and water glass.