soapstone instead of FB Board

[Dagored154]

A friend of mine has sold me enough 3 1/2" soapstone bricks to place under the firebricks. he has also suggested splits on top of the full firebrick for the cooking surface. he has built many commercial pizza ovens and residential ovens over the last 40 years using this method and he highly recommends it. he is a very experienced hobbiest bread and pizza maker as well. I enjoy his enthusiasm and advice. But some on this site have concerns about the lack of FB insulation underneath the bricks. I don't think my friend would steer me wrong however I would like to hear from other experienced oven builders. what are your thoughts? thanks for sharing.

[deejayoh]

Re: soapstone instead of FB Board

Soapstone is a heat conductor, not an insulator. You could put it under your firebrick if you want a super thick heat sink, but you will still need an insulating layer of FB board or vermicrete. Otherwise your heat just passes through the firebrick and soapstone and gets sucked into your concrete hearth

[Dagored154]

Re: soapstone instead of FB Board

Thank you Deejayoh. I hear you and will contact my friend when he gets back from Canada.

[Les]

Re: soapstone instead of FB Board

But some on this site have concerns about the lack of FB insulation underneath the bricks..

It's not a concern; it's a fact. I don't know who your friend has been building for but we know insulation is your friend. There is a possibility that they dump an incredible amount of energy into the oven and it would retain the heat (think Allen Scott). It comes down to what you want your oven to do.

[azatty]

Re: soapstone instead of FB Board

It's not a concern; it's a fact. I don't know who your friend has been building for but we know insulation is your friend. There is a possibility that they dump an incredible amount of energy into the oven and it would retain the heat (think Allen Scott). It comes down to what you want your oven to do.

You said "bread" and I immediately thought of the Scott design. The double layer your friend is using sounds very much Alan Scott's design. Or the Masonry Heater folks.

Insulation under the hearth keeps the heat from conducting from the brick into the structural slab, which is a massive heat sink. The triple layer of bricks without insulation will heat up nicely, but it will also cool down faster because the multiple layers of brick and the slab pull the heat from the surface of the hearth bricks untill the temperature equalizes. What you get is an inefficient oven. Sure, it works, but it can work better with insulation. It doesn't need to be FB board. It can be vermicrete or perlcrete or any other high temperature insulation.

[texassourdough]

Re: soapstone instead of FB Board

Adding soap stone below the hearth adds mass. That alone is not necessarily good or bad, depending on what you want from the oven. OTOH, thinking of soapstone as a replacement for insulation is simply WRONG for as discussed previously it is a relatively good conductor.

The real question is what is your intent for the oven. Having excess mass means more firing time to get to operating temps and having too little means having baking temps fall too fast - particularly on multiple bakes.

If you add mass under the hearth, you should probably add it to the dome as well or you will directionally be imbalanced.

But most of all you need to think about how many "batches" of bread you plan to bake at 12 to 20 pounds of dough per batch. Your friend seems to be designing ovens more for bread than pizza (whether barrel vault or pizza design you don't say). If your plan is pizza only or single batches of bread there is little if any benefit to his design over a well insulted Pompeii design based on the collective experience of this forum.

[texman]

Re: soapstone instead of FB Board

Dagored
Glad you are getting some advice to get you going. Keep that thread going and post lots of pics.
Tracy