hearth insulation layer

[Alex uk]

Hi, I've just bought a wfo from a shut down small restaurant & rebuilding it in my garden. The plans I have recommend using a 1" lean cement (9 parts sand 1 part cement) on top of the concrete hearth support, and then their fire bricks, 30mm deapth on top of that. Having read your Pompeii plan (excellent by the way!) there doen't seem to be enough insulation in my oven hearth? I guess the sand is acting as insulation but is it enough? Can anyone advise? Many thanks, Alex

[david s]

Re: hearth insulation layer

Sand is not a particularly good insulation material. In the case of a 9:1 sand, cement mix you will be getting some air space around the sand which will act as an insulator, but it is not a particularly good result. A 5 or 6 :1 vermiculite or perlite mix will provide many more spaces in the resulting mix and give you a way better performing insulating layer.

[dmun]

Re: hearth insulation layer

1" lean cement (9 parts sand 1 part cement) on top of the concrete hearth

Not only is sand a particularly poor insulator, like the gravel and broken glass that are sometimes cited, but one inch of anything is not nearly enough insulation. David's suggestion above of a vermiculite mix is a good one, but you will need at least four inches of vermiculite concrete. If you are pressed for space, you can substitute two inches of refractory insulation board.

[callan88]

Re: hearth insulation layer

Go with the refractory insulation board. I tried a single layer of firebrick atop an insulating layer of sand and consider it now to be a huge mistake. I'm losing so much heat through the hearth that I often have to rake coals out onto the hearth between pizzas to get the temperature back up again. I built an 1100 degree monster fire two weeks ago that kept the hearth hot enough, but it had to be watched very carefully because the top and edges of the pizza were incinerated after little more than a minute.