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Granite is a highly variable material. One success does not insure universal success. Nor does one heat up/cool down cycle represent a lifetime. I have built fires on clean granite (clean, no granular material, natural granite as in mountains) and have heard it pop and found granular material in the ashes. Obviously that granite does not represent all granite either.
Why you want stone or tile as an oven floor? Please understand that I'm not trying to dissuade you from preferred choices, I’m just asking. Relative to Soapstone I did a bit of research and posted some info in the Pompeii build forum.
I know there is a bunch more to uncover relative to this but it might give you a head start. What I have come away with is that if you choose something other than firebrick brick naturally you need to adjust the build to embrace the material’s nature. Soapstone is more conductive than is firebrick and so this seems to be a plus for a pizzeria where you want to get pies in and out I a real hurry but it may not help a person only wanting to do pizza for a small group. I can’t really say if this is a plus or not.
Bread bakers seem to shun soapstone in their ovens. Some say the bottoms can burn before the center or outside of the bread is done cooking, I don't know.
I can comment on using a thin 3cm slab in my gas range and I’m very happy with it so far.
If you’re looking for a stain free surface for your oven, Soapstone can work well although know that the firebricks within the oven are really self cleaning with the next fire. Firebricks in the entry area are an irritation for some. This area doesn’t get hot enough to cook off the spills and any porous material here will get some staining with use. I replaced my entry firebricks with a slab of Soapstone and I like the clean non porous surface, this said I’m planning to swap it out for the same granite that I have on my counters. I don’t believe that the lower heat in this area will be a problem for this granite. Another aspect of the Soapstone is because it is more conductive I would expect the concrete hearth to get hotter sooner with the same insulation than an oven with a firebrick floor would.
well put Chris, it all depends on what your trying to accomplish. Putting some exotic matl, especially on the floor, puts you into unproven design situation. Soapstone is the only alternative to firebrick matl this forum has any experience. You are going outside the design experience and you would have to do all the characterization work yourself. You might find out some other material may not be a good solution for this application.
Ask yourself why you want to use a different material and present it here for comments. You may just end up with firebrick. Remember, once you have used an alternative material, it is cast in stone (or concrete) and not easy to change. IMHO.
When I built the oven I set the floor using firebrick directly on 2" of rigid board insulation. In this configuration I was able to saturate the oven and hold cooking temperatures, from 850F cooling down to 250F over 72 hours without burning additional wood. After I swapped the brick in the entry area to soapstone I found that I had 2 days of cooking temperatures, from 850 down to 250F. Part of this I attributed to the saturation of the oven in the first instance, maybe. Part of this I attribute to a change from an IR thermometer to a dial set in the door, maybe. But, at the time, I had the feeling that the design change was a major part of the differences that I was seeing. During the little bit of Soapstone research that I was able to do, I found that it transfers heat 6 times faster than does brick.
I think that the Soapstone in my entry provides a path for heat to be conducted from the interior of the oven. My solution is to cut a thin piece of rigid insulation to create a thermal break between the firebrick floor and the entry floor. I think this design change will make a big difference in the heat retention and the duration of cooking time in my oven. This is only my example of how I think the material, in the entry, unexpectedly changed the oven performance. I'm sure that some of what I was seeing relates to the thermometer change and saturation of the oven but I'm convinced that the soapstone is acting as a conduit for heat to escape.
The reason that I’m moving to granite is for aesthetic consistency. I would have gone directly to granite but I didn’t have enough comfort that the granite would hold up. Some forum members are using similar granite for their entry and are not experiencing problems, so I’m going ahead with this material change and will include a small thermal break.
That soapstone or granite would cool your oven without a thermal break is not surprising. Grainite for the entry (with a break) should pose no problems so long as you don't set scorching/glowing skillets and stuff like that on it.
The oven floor is arguably not as critical for pizza as for bread. Part of the character of a traditional WFO is the rate of heat release back to the oven after loading and closure. High conductivity materials like soapstone and granite would be expected to give a different crust (and interior temp) from a brick oven. A