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Post by tallgrass on Jan 30, 2016 11:30:05 GMT -8
I was wondering if its possible to use a non refractory material to cap a heater without paying for expensive refractory mix or firebrick tiles. I know an 8" batchbox throws a ton of heat, but I thought I would ask if anyone has tried to use regular concrete pavers with KAO-wool or other ceramic paper mortared to the bottom. I understand it doesn't hold up as a riser material without a ridgidizer, but the velocities of gas movement should be much lower at the point of the capping slab and I feel like there would be less deterioration that would occur? Has anyone tried this?
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Post by peterberg on Jan 30, 2016 12:10:45 GMT -8
Normal concrete will break into pieces when exeeding 572 C / 1060 F, a temperature which is easily obtained. It'll almost certainly crack long before reaching that point.
Personally, I tried it with a just so-so rocket (my first), while the riser end was about 1.5 m / 5 ft away from the top. The heater wasn't optimized at the time, I wouldn't dare to use it like that with a recent heater. What you could do: use large pavers and glue some 2.5" of superwool underneath. No guarantees it'll hold.
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Post by patamos on Jan 30, 2016 13:04:14 GMT -8
I have wondered about cob/adobe slabs with fiberglass strands in place of the chopped straw
On a bench bell i did two years back i applied cob to the underside of 2'x2' concrete slabs then more cob on the top side to create a 5+" top deck. I also rounded off arches where the deck meets side walls and columns to add strength. Not as hot as the top of a batch box bell, but holding up well so far.
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Post by peterberg on Jan 31, 2016 1:04:07 GMT -8
Sidewalk pavers are perfect for benches, most of the time it's done as a double layer with overlapping joints. The top of a bell, being right above the riser is much hotter. Maybe building a cob arch? I wouldn't know how to that, but it do sound like a viable option to me.
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Post by patamos on Jan 31, 2016 12:04:29 GMT -8
Ya that makes sense I am not sure of the best ratios of the cob mix for this application, but i would be inclined to include cow manure and a bit of horse manure in place of straw. The fibre is there mostly to keep things from cracking, but the finer fibres are used in place of straw so that no real cavities are left when they burn out. The nice thing about the arch is that it ought to hold up even if it does crack here and there
Donkey has written a good explanation of his high heat cob mix (which also has wood ash). It might be found in the reference category on this forum.
I think Matt Walker has experimented with blending roxul (spun mineral wool) with sodium silicate and clay to form his feed chamber. Getting materials evenly blended would be important here. This is why i am curious to try fiberglass filaments.
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