roy
New Member
Posts: 38
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Post by roy on Jan 18, 2012 4:44:31 GMT -8
after years of thought and finally finishing the building which will contain the cob bench, ive ordered the bits for the RMH.
i still have loads of questions but the main one at the moment is what to construct to sit the burn tunnel on. i plan to pull up a couple of slate flag stones which are sitting on earth. i want to sink the RMH down a bit. my thought was to pour a small concrete plinth for the bricks to sit on? i know ive had the answer to this question when ive looked in the past.
i plan to use fire clay to cover the burn tunnel and to construct the junction between barrel and flue. the bench should be sub soil from digging the foundations for the convervatory.
8" flue around 25'
many thanks
chris
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Post by Donkey on Jan 18, 2012 8:29:24 GMT -8
Concrete is likely to crack (heat shock). Still.. Cracked or not, it'll hold up the works.
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roy
New Member
Posts: 38
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Post by roy on Jan 19, 2012 7:57:01 GMT -8
donkey, are there any other options which wont crack? fire cement? i might not be able to bury the RMH and therefore have to place the slab on the slate foor, any ideas how thick the slab should be.
thanks chris
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Post by solarbas on Jan 19, 2012 9:27:56 GMT -8
Hi everybody! roy, perhaps it is possible to insulate the burn tunnel from your concrete slab by using foamed glass or vermiculite with clay/cement. That way the concrete will experience less thermal stress and the burn tunnel will be hotter, improving combustion. Bas
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Post by canyon on Jan 19, 2012 12:32:59 GMT -8
I second solarbas on his suggestion of foamed glass. The stuff is wonderful and not too expensive. I have built several rocket combustion units on top of it and as long as you are careful in laying the firebrick it can handle the load. I suggest setting the foamed glass in a clay/sand mortar bed to level and get proper support. Perlite or vermiculite clay can work too but for me it is usually worth the $30 or so dollars for the ease of the foamed glass.
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roy
New Member
Posts: 38
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Post by roy on Jan 19, 2012 12:58:02 GMT -8
thanks canyon. im not sure what foamed glass is in the UK.
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Post by canyon on Jan 19, 2012 19:48:47 GMT -8
Check with masonry stove builders and supply houses or ceramic kiln/refractory suppliers, it is common in those lines.
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roy
New Member
Posts: 38
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Post by roy on Jan 19, 2012 23:46:53 GMT -8
found some, but i dont want to insulate the floor. i want to heat the slate floor and use the earth as more thermal mass.
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Post by canyon on Jan 20, 2012 10:03:33 GMT -8
Sounds like just a good bed of clay/sand mortar is in order then.
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roy
New Member
Posts: 38
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Post by roy on Jan 22, 2012 8:11:39 GMT -8
thanks canyon.
i dry stacked the burn tunnel in the garden yesterday and it worked nicely. plenty of draw sideways and a rocket noise even though the wind was very strong and swirling around. planning on laying the foundations in a week or 2 and then dry slacking again before i mortar the bricks.
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