Oven base insulation

[pizzahead]

Hi. I have a 40mm (bit less than 2") calsium silicate insulation board for underneath the oven floor. Does anyone think that this is not enough insulation. The board is sitting on a concrete hearth 100mm (bit more than 4") thick.

Thanks
Jase

[asudavew]

I used vermcrete, but I think you need at least 2 inches of cal sil

You could use a couple inches of vermcrete and then the cal sil board.

Don't skimp here my friend. The more insulation under the floor the better.

Dave

[james]

I'll agree with that. The thermal calculations show that 2" of ceramic insulating board (Cal Sil or Alu Sil) is a little better than 4" of vermiculite concrete. The 2" thickness takes a 1000ºF face down to something reasonable at equilibrium -- which works well for a home brick oven that will operate for hours at a time, rather than continuously.

If cost isn't too big of an issue, go thicker.

James

[pizzahead]

Thanks for the advice. Actually 40mm is a bit less than 2" not 1" - is it still worth laying down maybe 2" of vermiculite/cement? That would mean I would have 40mm cal sil board & 50mm vermiculite/concrete?

Cheers
Jase

[james]

Hey Jase,

.393 x 4.0 = 1.572". I should have caught that. :-)

If you lay down 2" of vermiculite concrete under your Cal Sil board, you will be in good shape. That would not be expensive, and not require too much effort.

Nice idea.
James

[pizzahead]

Thanks James. Purchased the materials at lunch today and will lay it tonight. How long should I wait for it to cure before I lay out the Cal Sil board and base for the oven?

Also the mix is 5 parts vermiculite to 1 part portland cement, roughly how much water is needed to get a good mix.

Thanks again.

Jase

[james]

Jase,

You can do it by sight and feel. Think oatmeal; Scottish oats. You can set your boards on the damp vermiculite concrete, and let it all cure. The boards are light and will not sink or compress the vermiculite.

If you give that a day or two to set, you should be fine.

Would other builders agree with that?

James

[pizzahead]

The boards are very light yes, but how long before I can lay out the firebrick oven base and start the dome do you think?

Thanks again.

Jase

[james]

As soon as the vermiculite layer is dry enough to not compress.
James

[pizzahead]

Thanks for your help James. I laid 75mm (bit over 3") of vermiculite concrete last night and it looks good this morning. That plus the 40mm cal sil board and I should have plenty of insulation for my oven.

Cheers
Jase