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Post by pete123 on Jun 27, 2012 19:24:43 GMT
I collected my Vermiculite (with a healthy WFO Jewson discount - thanks). It is Silvaperl V4 branded. There is no mention on the packet of agricultural use. All the info on it states the insulation properties including fireproof and irritation free. it is a brownish colour and looks like cereal or wood-chips. Photo attached in case anyone is interested in what it looks like. Attachments:
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Post by pete123 on Jun 27, 2012 19:35:09 GMT
I've bought some waterproofer from Screwfix for when it's time for the render. www.screwfix.com/p/no-nonsense-integral-waterproofer-fluorescent-pink-5ltr/43947On the back of the can it says "A liquid admixture designed for use in reducing water absorption and making cement less permeable..." and "Specifically designed for use in rendering finishes such as harling, dry dash and pebble dashing" It sounds ideal for the render to me. Does anyone see a problem adding it to the vermiculite concrete? Is that a good idea? Don't panic though I won't be pebble dashing my oven.
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Post by cannyfradock on Jun 27, 2012 19:44:14 GMT
Pete
Great repair job. I have tried to look back over your build to see the interior bricks where the crack has appeared....but the only vertical joints I can see are on the left hand side of your dome.....your cracks seem to come from the rear of your dome. I have also noticed that you have put smaller bricks in the rings to avoid vertical joints one on top of the other. (it's difficult to find a specific part of your build as your thread is very popular with 15 pages and over 2000 views....I love it!!!.)
The homebrew is supposed to be as strong as the fire-bricks themselves so I can only think that there was still too much moisture in the dome when hard firing for the cracks to appear like that. If that was the case then when the water left in the dome was exposed to too much heat....and the water expanded, it would find it's weakest point to expand.......the mortar. The natural form of a dome means it can't go anywhere, so the crack will just be a pain in the arse in aesthetic value. Something to give you piece of mind would be to place some strips of ex-met...or chicken wire over the exterior joints (about 4" wide).....this should help any future cracking. (homebrew or wet lime and sand will help hold this in place)
Don't worry.....you're getting there. Love your build.
Terry
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Post by pete123 on Jun 28, 2012 20:23:30 GMT
Thanks for the above advice Terry. This is the insulation. Not a brilliant photo. Attachments:
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Post by pete123 on Jun 28, 2012 20:25:37 GMT
The first layer 25mm thick went around the circumference. Attachments:
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Post by pete123 on Jun 28, 2012 20:31:09 GMT
I was a bit concerned about running out & it all needed covering twice. So perhaps a bit unconventional but the next bit went front to back - to cover the top and double thickness at the back. I also trimmed some excess (overlap) from the first bit to fill in the triangular gaps. Attachments:
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Post by pete123 on Jun 28, 2012 20:40:59 GMT
This bit goes from side to side. So most of it is 50mm now. With the leftover bits filling in the gaps and the very last bit plonked on the top front bit. The only bit with 25mm is the little bit in the photo where you can just see the thermocouple wires poking out (on the left.) It's the same the other side. Extra vermiculite concrete will cover it. Attachments:
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Post by pete123 on Jun 28, 2012 20:44:11 GMT
A couple of screws kept the chicken wire in place. You can see the small bit with just the one layer of insulation better in this photo. Attachments:
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Post by pete123 on Jun 28, 2012 20:48:22 GMT
With the wire on. The upper bits of wire aren't doing an awful lot. Hopefully they are on enough to stop the wind blowing them away before I can get the vermicucrete on. Attachments:
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Post by pete123 on Jun 28, 2012 20:49:34 GMT
...and for completeness the other side. Attachments:
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Post by bookemdanno on Jun 28, 2012 21:18:53 GMT
way-hey!! All tucked up nicely!! Now the joys of VERMIIIIICCCRRRREEEETTTEEE...mwahhh haa haaaaaaa!!!!!!!!!!!
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Post by faz on Jun 28, 2012 21:30:09 GMT
It's not too bad, don't listen to him
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Post by pete123 on Jun 28, 2012 22:37:11 GMT
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Post by bookemdanno on Jun 29, 2012 6:18:21 GMT
Thats rather handy pete! Well done!
I think Terry has another method of pre-soaking the Vermiculite overnight, then mixing a cement/water slurry first before adding the Vermiculite later. It no doubt adds a lot more water to the mix but if it's allowed to dry out slowwly and fully its not an issue. Terry may well have initially tried the "book method" and then created his own for ease of workability around an oven form. I'd say 6 or 7 to one would do. You want as much Vermiculite as possible with just enough cement to bring it all together. Not sure that the waterproofer would do much as the Vermiculite mix looks to be quite open in texture. Sort of like a handful of damp Sugar Puffs. I've not yet to have the pleasure of Vermicrete though. IMO a good waterproofed outer layer will do fine.
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Post by bookemdanno on Jun 29, 2012 6:48:27 GMT
I meant to add. It seems to be hard to get the Vermicrete to hold, even with the wire mesh in place. I'm not sure i'll use Vermiculite as i've got an insulating render, a bit like Segrelime for my oven. I'm thinking of making a runny slurry of Hydraulic Lime/water and flick this at the mineral wool to let it crust up and create a peaky key coat around the wire mesh. My thinking is this'll make the mineral wool insulation a slightly harder substrate to work onto and the crust will give a bit of suction for the next layer. It'll be a messy old job though!
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