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Post by Calaf on Feb 6, 2012 21:14:46 GMT
My stack of 16 storage heater blocks. They had been sitting outside for several months so I put them in the oven in batches of 4 to dry out. The fan oven took 1 hour to raise the temperature to just 120'C. I tried to get them to 240'C but after 2 hours they had only reached 190'C.*** This exercise tells me Turkey was right to suggest laying firebricks flat on the oven floor. They are thermal sponges. My neighbour has also donated 4 firebricks. They appear to be 50mm rather than the usual 76mm. I may use them as the keystones in the oven vault. Edit: *** Turns out the oven's thermostat was broke.
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Post by Calaf on Feb 6, 2012 21:16:30 GMT
Hey Calaf, Nice pile of bricks you have there, Very similar to what I have. Nice work on the base... Looking good! I don't know if you need to cut them? But if you do a Segmented Dimond Blade in a angle grinder works very well. (just cut a whole bunch myself) The bricks seem very hard but this blade went through it very easily! I soaked them in water for a couple of minutes before I cut them and it kept the dust down. Merry Xmas Rich361 Hi Rich, My bricks are profiled one side ... I suspect this makes getting a clean split more difficult unless you cut all the way through. I want to avoid cutting these if I can. The vault arches will be regular firebrick as I only have 16 of these.
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Post by Calaf on Feb 6, 2012 21:17:48 GMT
storage heater bricks rock! Good to see all you guys using them, they really do make for a perfect hearth, and as you say are a great heat sink and are great to cook on merry xmas cheers marcus Hi Marcus, I'm hoping they have the same thermal properties as the regular firebricks. Would be interesting to hear from someone who has used both. I usually throw money and technology at projects like this but this time, finding myself in a state of involuntary early retirement, I thought I would try and be economical and recycle stuff laying about the garden. And it's fun.
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Post by Calaf on Feb 6, 2012 21:18:37 GMT
I hope everyone has enjoyed fillinging their bellies and bladders this Christmas. But as we gorge ourselves, let us not forget the true reason for the season... 23.4394° axial tilt of the Earth's rotational axis. Build is on schedule, following the weirdly clement weather, with base structure complete. Five 38mm pavers laid to provide a platform for the oven build. Costs 4 - 600x600x38mm pavers ------ £20 B&Q 1 - ditto ------------------------ £0 recycled Total --------------------------- £20The final render and featheredge timber finish to the front will cost another £10. Total cost of base: £62.
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Post by Calaf on Feb 6, 2012 21:22:04 GMT
Hey Calaf, Great looking base! I found with my build the base was the most time consuming part. The oven was the quickest part, I hope you foind the same! You will be cooking before you know it! Merry Xmas and Happy New Year!! Rich, I don't think I can come close to the speed you finished your oven. But I'll try.
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Post by Calaf on Feb 6, 2012 21:22:48 GMT
I now have a platform of 1.2m x 1.5m on which to commence phase 2 of the oven build. I had planned to lay a ring of 8 celcon blocks and place a ceramic fibre board over to provide the hearth-base isolation. However, conscious of the need to avoid adding unnecessary height to my "compact" oven, I decided to go with a perlite mortar raft of 40mm. (And I have some perlite to get rid of anyhow.)
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Post by Calaf on Feb 6, 2012 21:24:22 GMT
Hi Calaf, you're making good progress. One thing for you to consider, its not clear exactly how close to the front the wfo will be when finished but one practical thing you need to consider is that the further away the cooking area is from the front the more difficult it is to load (wood and food) particularly if you plan on roasts and stews. Because of the height of wfos, there's no bending from the waist so the furthest you can easily get stuff into the oven is about arms length. I think this is probably more important for barrel design than pompeii. Hi Tony Thanks for the headsup. I'm fumbling in the dark on this so appreciate all the input I can get. Because of the limited space I hadn't really considered reach within the oven, assuming it would be smaller than most others. I'm planning on a cooking floor of 600x920mm (WxD, essentialy determined by the brick sizes) with a short landing. If you think it advisable I could reduce the depth of the oven by 115mm by cutting a half-brick arch.
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Post by Calaf on Feb 6, 2012 21:25:57 GMT
Hi Terry, this is my current thinking on the hearth/oven floor. Perlite mortar raft in lieu of blocks, 15mm ceramic fibre board for isolation and Firebricks laid flat per Turkey's suggestion.
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Post by Calaf on Feb 6, 2012 21:27:27 GMT
I think you'll be ok with those measurements particularly as the fire in a barrel oven is usually at the back. Its just that most people think having a large landing is good for temporarily storing things but forget that the height of the wfo means manoeuvring food into the oven difficult. Its really just a heads up practical thing to think about. Thanks Tony, I'll keep in mind the ergonomics. The short landing I'll keep to a minimum and will probably be determined by the chimney provision.
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Post by Calaf on Feb 6, 2012 21:28:12 GMT
Now, feeling thrifty I have reappraised the firebrick arrangement. There are 8 bricks (in the 2 outer floor rows under the walls) that, not being fire-facing, could be replaced by 37p engineering bricks. That would save £5.04p which I could spend at Tesco on their 4-for-£5 beers. Every little helps.
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Post by Calaf on Feb 6, 2012 21:29:06 GMT
On another forum I read folk were using perlite at a ratio of 10-to-1. This seemed a bit weak to me so I thought I would do my own tests. A few days ago I made up some 40mm cakes of vermicrete and perlicrete (?) as an experiment at 9:1 and 5:1, to determine their mechanical and thermal properties. Here are my observations. At 9:1 the perlicrete, although crumblier at the edges, seemed stronger in compression than the vermicrete which after drying for two days still had a bit of a spring to it. The vermicrete took several more days to set properly. Perlicrete was prone to pooling of the portland if the mix was too wet. Not surprising as perlite is used in gardening for drainage, vermiculite for water retention. At 5:1 the vermicrete set well but still seemed weaker than the perlicrete in compression. However, it was superior in resisting shearing and tension. I can see why people use this to span voids or cantilever. Using an Infra-Red pyrometer I found that thermally the vermicrete was slightly better at insulating from a blow-torch on full tonk for 1 minute, averaging over 4 readings a rise of 8 degrees on the opposite side where the perlicrete rose by 11 degrees. I was surprised by that, expecting the perlite to do better, and suspect it might be that perlite is more porous to gases. To work with the perlicrete was awkward. You have to get the water content just right and it doesn’t stick well. The vermicrete had better cohesion and seemed to me to be a better choice for vertical rendering. (But note my experience is at odds with the FB forum 'experts' who claim the opposite.) I shall use the perlite merely because I have 50 ltres in the shed but will add some vermiculite to help prevent pooling when wet.
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Post by Calaf on Feb 6, 2012 21:29:58 GMT
Thank you Calaf for a perfect insight between the qualities of Perlite V's Vermiculite.....Please keep us informed on your progress. Myself I have never seen perlite on sale, although I have seen it on the www. Terry Terry, best place to buy Perlite is your local "weed" shop (hydroponics). £15/16 for a 100 litres bag. One thing I didn't mention is that it is a pig to level. It's like Rice Crispies, only not as tasty, and the Perlicrete mix is just like chocolate Rice Crispies cakes.
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Post by Calaf on Feb 6, 2012 21:31:18 GMT
Christ on a bike! This weather is insane. Lots of clearing up to do including a shattered pane in the greenhouse. But the wife wont take any excuses and has commanded me to go out in the garden and get cracking on the oven. Have made a start on the perlite raft, 40mm deep... The outer ring was a 4:1:1 perlite, vermiculite and portland mix. The inner part 8:1 perlite and portland. The reason for this being the load stress is at the periphery and more thermal stress in the middle. I've chosen perlite rather than vermiculite, despite my above (dodgy) thermal resistence test, because the ceramic fibre board will provide a convection barrier so theoretically the perlite will perform better. About 40 litres of perlite was used.
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Post by Calaf on Feb 6, 2012 21:36:18 GMT
That's looking grand there. Remeber it's the air trapped in these materials that is the insulator, so you want the mix as light as you can without compressing it too much. Very interested to see the differences in materials. Cheers Marcus Hi Marcus, Good point about air. Perlite is easily crushed so I mixed it in a bucket with a garden trowel, folding like cake mixture. Unfortunately the mix doesn't flow like concrete so you have to push it into the corners, tap it down and level with a floor trowel. Treat it like food rather than a building material.
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Post by Calaf on Feb 6, 2012 21:37:03 GMT
Ever-mindful of keeping the oven as compact as possible, particularly depth-wise, I’m going to make the aperture a half-brick (115mm) in depth. This reduces the brick count to 5 for the aperture and will make reach within the oven easier per Tony’s advice. Hoping those firebricks are easy to split.
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