Forestsmith Posted December 28, 2020 Share Posted December 28, 2020 Hello! I’m building my first propane forge and I have been reading about various forge designs and I had what I think is a good idea pop into my head. I absolutely love soapstone, and I am ordering a slab for my kitchen counter, why not use the remnants for the forge? It looks like soapstone can handle up to 3,000 degrees (I have a soapstone woodstove) but not sure about the insulating value. When my woodstove fireplace is ranging hot its about 500 degrees on the sides. However that is with firebrick as well. Has anyone here tried this? Any thoughts? Thanks! Link to comment Share on other sites More sharing options...
George N. M. Posted December 28, 2020 Share Posted December 28, 2020 A couple thoughts: -Soapstone or steatite is metamorphic rock composed of talc and other minerals and will stand pretty high temperatures without degrading. -It is fairly dense and will act as a heat sink more than other materials. It is often used in wood stoves as a heat sink to radiate heat. This will be a drawback if you are thinking of using it as a shell tor a propane forge. You want your energy to go to heating metal, not the body of the stove. This will be somewhat mitigated by insulation inside the forge. -It should be fairly resistant to thermal shock because it is only moderately brittle compared to other rocks. -Soapstone often has varying amounts of asbestos in it. Therefore, you should be VERY cautious about dust generated when cutting it. Do NOT rely on any assurances given by the stone yard where you bought it or the counter installer. They know less than nothing about the geology of the slabs they sell. They MAY know the country of origin but that is about all. -Generally, soapstone used for counter tops has less talc in it and is harder than the stone used for carving and sculptures. -Generally, I would say the soapstone would not be my first choice for forge construction. You did not indicate if you are talking about a box for a solid fuel forge or the shell of a propane forge. It might work better for the former than the latter. "By hammer and hand all arts do stand." Link to comment Share on other sites More sharing options...
pnut Posted December 28, 2020 Share Posted December 28, 2020 It's used as a tue stone. I've never heard of an entire forge being made from it. Pnut Link to comment Share on other sites More sharing options...
Forestsmith Posted December 28, 2020 Author Share Posted December 28, 2020 I should have specified, this will be a small to medium sized gas forge. I was thinking using soapstone as the shell and still lining with fire brick. Link to comment Share on other sites More sharing options...
Frosty Posted December 28, 2020 Share Posted December 28, 2020 Soapstone, talc, asbestos, jade, and similar only really differ in the molecular water content and the dust is ALL a serious breathing hazard. Soapstone is used in stoves because is is relatively IR transparent, meaning thermal radiation passes through it pretty freely. Think visible light and window glass. It MIGHT work in a thin layer as a flame face though it's relatively fragile at forge temps. It's definitely NOT an insulating material so you'll need something that is an insulator for outer layers between it and the forge shell. Soft insulating fire brick might do it, Morgan Ceramics, K-26 is the best and most affordable I'm aware of and is available in Seattle and Spokane. Kiln shelf is designed to line high temp furnaces like a forge and is known to work. Small or large doesn't matter, you have to design for the environment and a propane forge is not only a high temp environment it's very chemically active and suffers rapid thermal cycling. Frosty The Lucky. Link to comment Share on other sites More sharing options...
ThomasPowers Posted December 28, 2020 Share Posted December 28, 2020 Neat idea; but not good one. I have a slab of soapstone that was a laboratory bench top that I used under a propane forge to protect the wooden work bench it was on , made a nice place to set hot items and tooling too. I originally got it for making soapstone spindle whorls based on dark ages finds. Link to comment Share on other sites More sharing options...
Forestsmith Posted December 28, 2020 Author Share Posted December 28, 2020 1 hour ago, Frosty said: It MIGHT work in a thin layer as a flame face though it's relatively fragile at forge temps. It's definitely NOT an insulating material so you'll need something that is an insulator for outer layers between it and the forge shell. Soft insulating fire brick might do it, Morgan Ceramics, K-26 is the best and most affordable I'm aware of and is available in Seattle and Spokane. Kiln shelf is designed to line high temp furnaces like a forge and is known to work. I actually didn’t consider it as a liner, but I think I may experiment! I appreciate the firebrick suggestions, I will most certainly check into it. The soapstone, however does, not sound like an ideal material, but I do think it may have a place in my forge build, even if its my table top next to my forge. I still may give the lining or shell a try, considering I will have a significant amount available. I will keep everyone posted on my results! Link to comment Share on other sites More sharing options...
Frosty Posted December 28, 2020 Share Posted December 28, 2020 I don't, I think it's a dangerously bad material to line a furnace, especially one you're going to be jamming steel into. You WILL abrade it and the propane burner WILL blow the dust into your breathable. You might as well wear an asbestos face mask. My advice is to choose a proven forge design and follow it. I prefer the insulating outer liner to be rigidized, 8lb. Kaowool, and Kastolite, water setting, high alumina bubble refractory for the hard inner liner. While not perfect for the flame face it IS durable and chemically resistant enough to serve. However a good kiln wash is icing on the cake, making the flame face impervious to: propane's highly reactive flame, the extremely caustic nature of borax based welding fluxes, and is very mechanically robust. Cold sharp steel bar will skate off it at yellow heat. Make side tables, serving trays, hot plates/trivets, etc. from your leftover soapstone counter top material. It's beautiful stuff but there are much less dangerous things to use it for. Frosty The Lucky. Link to comment Share on other sites More sharing options...
Glenn Posted December 28, 2020 Share Posted December 28, 2020 If soapstone were good material to be used in a forge, do you not think you would have heard of it being used in that fashion before? Link to comment Share on other sites More sharing options...
Forestsmith Posted December 28, 2020 Author Share Posted December 28, 2020 Not necessarily. Soapstone in large quantities isn’t exactly readily available, as well as being heavy and expensive, those reasons alone would make it a poor choice, all of which would be negated if I already had it on hand. I also don’t know everything and so that’s why questions need to be asked! As far as asbestos, to help clarify for future concerns, I did a decent amount of research into that (im installing my soapstone countertop myself, so I do need to be aware of asbestos) and the commercially mined countertop soapstone is tested for it. I mean this day and age theyd get sued left and right if it did contain asbestos. However, old stuff or anything that did not come from a modern commercial mine would, for sure, be concerning. Link to comment Share on other sites More sharing options...
George N. M. Posted December 29, 2020 Share Posted December 29, 2020 F.: As an old geologist I'd want to know what mine, where it is located, and see the actual test results. Composition in a deposit can change quickly, sometimes within a few feet. I'd want to know where my slab came from versus where the sample was pulled. Relying on the idea that a company would be sued for negligence is similar reasoning to "They wouldn't put it on the internet unless it was true." (BTW, I'm an attorney, too.) You may be just fine. There is a lot of steatite out there with little or no asbestos contamination and it is the source material for talcum powder. You may recall that Johnson and Johnson got sued for asbestos in their talcum powder. Your call but at a minimum I'd make sure that any cutting or drilling I did was wet and that the cuttings and dust were not allowed to dry out before disposal. "By hammer and hand all arts do stand." Link to comment Share on other sites More sharing options...
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