dome insulation with calcium silicate

[neilos83]

Hello oven gurus. A quick question. I was planning to insulate my dome with the usual fire blanket and vermicrete. i've got the blanket but i am yet to buy the vermiculite and i've got some calcium silicate board left over that i didn't use on my base, would there be any value in using this instead of vermicrete and if so shound i put it on under or over the blanket?  i know the calcium board has good thermal value but is it as good as the vermicrete?
cheers.
NEIL

[downunderdave]

Mar 13, 2016 10:38:04 GMT neilos83 said:

Hello oven gurus. A quick question. I was planning to insulate my dome with the usual fire blanket and vermicrete. i've got the blanket but i am yet to buy the vermiculite and i've got some calcium silicate board left over that i didn't use on my base, would there be any value in using this instead of vermicrete and if so shound i put it on under or over the blanket?  i know the calcium board has good thermal value but is it as good as the vermicrete?
cheers.
NEIL

The calcium silicate board has better insulation qualities than vermicrete, but it won't conform to the curve of the dome easily. You'd have to cut it into pieces and fill in-between with vermicrete or bits of blanket.

[neilos83]

Ok, so if i did go for the calcium silicate option, do you think it best to lay 4" of blanket on top of my firebrick dome, and then 2-3" of calcium silicate board or would it best to lay the board and then the blanket? I like your idea of filling the gaps with vermicrete. I think i would try and cut the blocks to as good a fit as possible so there is as small a gap as possible. I do have a small amount of vermiculite so i could always do a thin  later of vermicrete just to make the shape of my dome.
Cheers.
NEIL

[diggerjones]

I would put blanket on first. This would make the dome bigger so board would go on easier

[downunderdave]

Mar 13, 2016 19:00:03 GMT neilos83 said:

Ok, so if i did go for the calcium silicate option, do you think it best to lay 4" of blanket on top of my firebrick dome, and then 2-3" of calcium silicate board or would it best to lay the board and then the blanket? I like your idea of filling the gaps with vermicrete. I think i would try and cut the blocks to as good a fit as possible so there is as small a gap as possible. I do have a small amount of vermiculite so i could always do a thin  later of vermicrete just to make the shape of my dome.
Cheers.
NEIL

If you are intending to do an igloo style outer, shell the problem you have is that the calsil board will leave you with a lot of flat surfaces making it difficult to get a nice spherical form to render the outer shell onto. You could of course just keep making the outer render thicker until you get it round, but this requires more material and more work. If i were in your position I'd sell the excess calsil and use the money to buy more vermiculite so you can vermicrete over the lumpy blanket. Tapping the surface with a trowel or piece of wood gets a great rounded surface to render on to. I find you need a layer of around an inch and a half thick, starting from the bottom and working up to the top, to get this method working well. I use a 10:1 vermiculite, cement mix with half a handful of clay per litre of vermiculite to help make a good mix that's sticky enough but lean enough for good insulation.
If you are building a dog kennel around the oven then you can throw in any kind of dry insulation over the blanket and not worry about the form or adding water that has to be eliminated.

[neilos83]

Thanks for the info. I think i will just use more blanket and then top with a thin layer of vermicrete and render. I see the issue with the board and shape so I think I will be best off selling it. Thanks all for your info.