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Post by DCish on May 8, 2014 4:00:23 GMT -8
Mint, your reply is helping my thinking along, thank you very much! The countertop fabricator works with both natural stone and composite materials. It's up to me to figure out which is which on the scrap pile. I'd certainly have to be cautious on that point! The composite ones do have a "chunks in resin" look to them, though, so it ought to be relatively easy to sort out.
On the list you link to, mortar is listed as between 7.3 and 13.5. With granite clocking in at 7.9, maybe the thing to do is to try to figure out which mortar is on the low end of the expansion spectrum, and mortar it together. It took me some noodling around to realize that soapstone (not on the list) is the same as steatite, which is listed at 8.3, not too far off from granite. That has me wondering how mortar can have such a wide range of expansion rates, which takes me back to Smarty's post proposing using Talc as a filler in an aluminae cement casting. Could I substitute dust from cutting the stone I use (soapstone if I finally find a source of scrap, granite as my fall-back choice) in place of sand in a clay-sand mortar mixture as a way to move the mortar toward an expansion rate closer to that of the stone? If cement at 10 and steel at 13 are close enough together to use rebar to reinforce concrete, perhaps a stone powder - clay mixture could be close enough to my stone of choice to stick the pieces together without cracking significantly?
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Post by bmeagle on May 17, 2014 21:59:28 GMT -8
Just keep in mind that the temperature difference, ie difference between maximum temperature that the material will experience with the stove running and the room temperature determine by how much the material will elongate at the thermal expansion rate. Concrete and steel works despite the difference because concrete structures experience relatively small temperature differences. RMH temperature difference is extremely significant.
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Post by bmeagle on May 17, 2014 22:02:49 GMT -8
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Post by patamos on May 19, 2014 9:57:32 GMT -8
DC, you might want to consider the effects of different kinds of sand mixed with the clay slip. Clay on its own (with enough water to make it workable) is bound to contract significantly with its initial drying. This will likely make for cracks regardless. So a clay-sand (or other) mortar aggregate makes sense. I built a downdraft chamber recently using a wide array of brick scraps and cob. Cracks were inevitable so i gave it a 1/2" or so of cob (4 parts sand, 3 parts finely chopped straw, 3 parts clay slurry - 70%clay 30% water). Let that dry and shrink. Then laid on a finish plaster - fiberglass - finish plaster sandwich. The fiberglass can be bought in rolls at any store that sells drywall supplies. s895.photobucket.com/user/patamos/library/?sort=3&page=1We fired this heater full blast for 14+ hours a day for over a month (drying out a house full of brown-coat plaster in winter...). And the only place any sign of cracking developed was where i didn't place the fiberglass. A quick repair of another layer took care of that. I suspect some of the older clay bricks will spall with time, but the idea is to repair the inner wall with the technique i used to seal the outer skin. For further away in the cooler sections of your bell you could embed looseweave burlap into a cob browncoat. This is a simple way to ensure a crack free outer skin without fretting too much about the aesthetics of your brick/stone/slab work. well being pat
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Post by DCish on May 19, 2014 18:37:39 GMT -8
Very good point, Eagle. The Wikipedia link has some formulas that look like they'll come handy.
Pat, your description of using fiberglass is reminding me of things that Karl has mentioned for making the stove core. Off to post on another thread. About mortar, though, So now I'm wondering about buying some refractory mortar and cutting it with soapstone dust to make a mortar that will be the right expansion rate. What do you think? Or with all the recent talk of sodium silicate as binder, maybe a sodium silicate / soapstone dust mix as mortar?
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