nixie
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Post by nixie on May 20, 2013 10:27:21 GMT
Going to get all the fire bricks out this week and do a lego type layout session to work out how to lay them. I've seen the 45deg option a few times and it does look good. I have 33 firebricks which should hopefully be enough, if it starts getting tight then the arch floor might miss out to start with.
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nixie
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Posts: 144
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Post by nixie on May 21, 2013 8:46:44 GMT
Had a few spare minutes last might so made a form for the rest of the arch. Unfortunately also discovered the right hand side of the arch is not attached! Must have knocked it while cement was going off as the brick didn't bond to the cement. Annoying. Anyway, pics below showing the form in place with cardboard wedges spacing the bricks out. I'm starting to get a proper sense of the scale of the finished oven now.
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Post by nordberg on May 21, 2013 19:13:50 GMT
Great pics of a work in progress!
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nixie
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Post by nixie on May 28, 2013 12:12:48 GMT
This is going to be a bit of a monster (picture) post as plenty of progress over the long weekend. First up completed the arch with gap at the back for chimney. Did this in the pissing rain which was interesting with the cement getting wet and my brother holding 2 umbrellas above us and the arch (got caught out by a heavy shower) While that was drying off progress on the main part of the oven was limited so we worked out the oven floor layout and cut the fire bricks to shape. We used a bog standard tile cutter for this as the one I had from doing the kitchen handles 25mm tiles, perfect for my fire bricks. Bricks cut, laid out and numbered. Next day was starting to lay the oven floor so first batch of clay mixed up. I ended up using way more clay in this part than I hoped because of height difference between the entrance bricks and sub floor thermal mass (read didn't put enough sand under the sub floor!). To protect the bricks at the front of the arch I used a spare section of tile edging. I'm hoping this will stop any tools catching and chipping the leading edge of the fire bricks. Yesterday I mixed up the second batch of clay/sand and finished the oven floor. As you can see in this picture I've used the off cuts of fire bricks to take up space below the oven floor where the main dome will go, this is to save clay. Most of this batch of clay is left over so I've double bagged and sealed it for use when the dome is made. I'm hoping to mix most of the clay up in advance so the actually dome building goes quicker. To mix the clay/sand I'm using a tarp type bag, one of the ones our council uses to supply for garden waste, as this means less mess and that its easy to turn the mixture over. Final bit for the weekend was placing of the chimney. This a cavity spanning duct brick that I came across whilst in B&Q. They also had one half the thickness, however I decided its easier to restrict a larger chimney if its too large than to increase the size of a smaller one.
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Post by nordberg on May 28, 2013 19:25:51 GMT
Looks great. Can you comment on your clay mixture? You bought clay didn't you? What ratio are you using.?
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nixie
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Post by nixie on May 29, 2013 8:43:04 GMT
Yeap I bought clay. I used a ratio of approx 2:1 sand:clay (by volume) for the mixture with sand straight from the bag. I used Wickes sharp sand. It work out as roughly 14l of sand and 7l of clay in my bucket. I then did a drop test which held together fine, but did not splat out (I also did a test with sand that was wetter and this definitely splatted). I think I could maybe get away with a bit more sand as the mixture did not crack when dropped. There doesn't appear to be any shrinkage ate the moment in what I've done, but still early days.
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Woody
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Post by Woody on May 29, 2013 19:08:59 GMT
Looks great! I might have to borrow your chimney design.
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nixie
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Post by nixie on May 30, 2013 9:10:02 GMT
Thanks. Borrow away, if its too big for your build there is also a slimmer version which is half the width, both cost around £5-6 in B&Q, probably cheaper elsewhere.
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nixie
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Posts: 144
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Post by nixie on Jun 10, 2013 14:06:03 GMT
Been a while since I've had any spare time to put into the oven. However got a good run at it on Saturday and made great progress. I had decided before starting on Saturday that I was marginal on clay, so to reduce the required amount first off was to get the base of the walls to floor height. I decided to start the insulation early and used roughly cut up (you can't see it so no need to be neat) insulating brick to widen the foot print. No separate pics of this but you can see it in the sand form pics below. Next up was the sand form. This is actually 75% bricks to but down on sand usage. It also has a cardboard form inside running front to back which gave me a line to work too without having to place the external form onto the dome. Once I was close the external shape was placed over and the dome shaped to it. A wet paper layer followed the sand, not very easy to apply in wind! If its useful to any future build make this layer thicker than 3 sheets. I didn't and in places this ripped when adding the clay. So finally time to add the clay. As I mentioned earlier I thought I'd be close on having enough clay, turns out I didn't so about a third of the way up I stopped trying to make full thickness walls and decided that completing the dome was more important. At this point I wished I was using garden clay and had a nice hole to get a bit more from. More clay is now on order and I hope to finish the dome on Friday. The second mistake of the weekend of to be too vigorous placing the arch from back in (to hold the sand back). My arch is now cracked on both sides and is loose. I'm not sure how to repair this at the moment, thinking of drilling out 2/3rds of the 2 broken joints (leaving enough to hold the arch up just) and then fill the gap with fresh cement. Any other suggestions? I'm going to be order a peel and seasoned wood this week too I think as firing is getting close. Also trying to decide on insulation. I've been thinking about either making a frame and using loose fill vermiculite, or maybe a body soluble fibre (super wool) blanket. A question for the brick dome makers, how thick a layer of insulation blanket is normal?
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Woody
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Post by Woody on Jun 10, 2013 20:41:52 GMT
Nixie,
I'm following you build with great interest as I am a few steps behind you.
On an earlier post you said you ordered 75KG of clay , are you saying that is not enough for your build?
Cheers, Woody
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Woody
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Post by Woody on Jun 10, 2013 21:49:14 GMT
Further to my last post, I found this guide on another site:
Oven dimensions – 80cm internal diameter, 40cm high.
- 125 – 175kg of clay - 10.5 – 14 bags of building sand (20 kg each) - A third to half a bag (100ltr plus size) of wood shavings
The former dome took 120kg of sand to make. The first layer, chimney and entrance took about 45kg (3.5 bags) of clay and 90kg of sand The second (insulation) layer took the wood shavings and about 19kg (1.5 bags) of clay. The final layer and chimney extension (made it a little short to start with) took about 60kg (4.75 bags) of clay and the 120kg of sand used for the former
That's way more clay than I had imagined, but good to know.
Woody
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nixie
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Posts: 144
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Post by nixie on Jun 11, 2013 8:55:43 GMT
Hi Woody,
Yes I ordered 75KG of clay to start with. I think had I not used some of this between the oven floor and sub floor that it would have been just enough to complete the inner dome and porch. I've been mixing it nominally 2:1 by volume with Wickes sharp sand. I say nominally as 1 bag of Wickes sharp sand is more than twice the volume of 12.5kg clay, initially I use a bucket to estimate 2:1 which left maybe 15% of the sand in the bag. Later mixes I used a whole bag as its easier to measure. Drop test was still fine. Later still I used a whole bag and the 15% from an earlier bag and it was still fine.
Those dimensions are the same as mine, I'll add though that I'm going for a 10cm oven wall. The outer layer measurements are scary!! Think I might look for alternatives the cost less for that.
I can believe the dome took 120kg of sand, I used 4 bags and had a huge brick pile in the middle too (I'd recommend doing this if you have spare bricks laying around as its saves cash and time).
I think my measurement will be something like 60-70kg clay with 6-7 bags sand for the dome.
Out of interest what site did that list come from? Sounds like it could be worth a read.
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Post by cannyfradock on Jun 11, 2013 15:12:51 GMT
Nixie
Regarding insulation.....on a clay oven, hay or wood chips are added to either the whole dome clay or more often added to the second layer. The principle being this will create a honeycomb effect in the dome giving more insulating value. The insulating blanket we use on brick domes is 50mm thick. If you want to "house" the oven then loose vermiculit will suffice for a clay oven.
Whichever route you take you will have to dry the clay out before the next step. Make your curing fires slow...but steady. If cracks appear be ready with some more clay to fill them while the cracks are open.......then leave to cool before the next curing fire.
Terry
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Woody
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Post by Woody on Jun 11, 2013 19:01:17 GMT
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nixie
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Post by nixie on Jun 17, 2013 13:28:45 GMT
Mainly a picture update this time as not a great deal to say. The dome is now complete. Used an extra 2 bags of clay to complete. Starting to mine the sand (and bricks). I stopped on Friday at this point as the arch was a little soft and did 2 burns of tea lights to help dry it a little. More mining on Sunday to empty the interior Start of the drying process. After a ikea trip at lunch I now have 200 tea lights to burn through over the next few days. You can see a bit of a crack on the arch transition that I'll fill in time. Also a bit of cracking from shrinkage by the arch. I'm hoping to get some proper fires going at the end of the week
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