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karl 07-10-2008 05:02 AM

Hearth insulation - Siporex
I am soon to start up the insulating layer on the top of the oven stand. I have seen the procedure to use Vermiculite or Perlite and cement (5:1). I have also seen that Forno Bravo advertise insulation plates as an alternative. Forno Bravo is a looong way from being able to supply me with materials, but I am speculating using 100 mm Siporex plates (SIPOREX -> Homepage) instead. It's a type of leightweight (porous) concrete.The U-value is specified (for 100 mm) to: 1.257 W/m2 K (no imperial units here!). Will this do the job?

Regards from Karl

karl 07-10-2008 09:42 AM

Re: Hearth insulation - Siporex
I have done some further investigations around this and the heat conductivity of the Siporex is about 0,114 W/mK while the FB ceramic board is quoted to have 0,111 W/mK (at 600 C). So the heat insulation properties of Siporex should be OK even for approximately the same thickness as a FB plate. May I should add some few centimetres in thickness to be sure. The mechanical strenght of Siporex is also very good.

My only "concern" in using it is that the sintering (thats when the heat insulation properties start to take permanent damage) is quoted to some 1000 C and the melting temperature to 1100 - 1200 C.

But will I ever have to worry about such temperatures in my oven? Even at hot-spots and short-term loads?

regards from Karl

asudavew 07-10-2008 12:18 PM

Re: Hearth insulation - Siporex
This is interesting ....

It says the fire reaches about 1000f .

I've seen threads where ovens have hit 1100f to 1200f or 600c

I've measured my oven in the coals at 700c, but I'm not convinced of the accuracy.

So I think you will be just fine.


karl 07-10-2008 02:05 PM

Re: Hearth insulation - Siporex
Yes, I think the Siporex will stand up to the task. Thank you for sharing your temperature measurements Dave.

regards from karl

karl 07-13-2008 10:24 AM

Re: Hearth insulation - Siporex

For your information I managed to find the ACC blocks recommended as insulation blocks for brick ovens. The recommendation is taken from:
Maine Wood Heat - Organic Wood Fired Ovens

You can find it on page 23 in their downloadable instructions. They call the blocks "Ytong (also called foam cement", but it is clear from the instruction that this is ACC (or Siporex as markedet in my country).
The oven brand is LePanyol which is a recognised company in this trade.

regards from Karl

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