nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 17, 2013 13:29:41 GMT
Thanks Woody. That sites one of the ones I had a good read of before starting on the project .
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nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 17, 2013 14:41:59 GMT
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Post by cannyfradock on Jun 17, 2013 16:52:44 GMT
Nixie
The oven looks really good. Of course the main problem with Clay ovens is shrinkage when curing the clay. On my own clay builds apart from general cracks appearing on the dome (I think I didn't add enough sand to a pure clay when donning the wellies), I have also had separation from the clay/brick arch area. I think this is due to the clay bricks ....already being dry, take most of the heat when starting the curing fires. The clay is naturally initially saturated with water so during the curing process, this junction of raw clay meeting kiln dried clay is going to act against each other?......On my next Clay build I will soak the brick arch in water when I start my little curing fires.
Hopefully some of the more experienced Clay oven builders will see this and give advice.
Terry
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Post by nordberg on Jun 18, 2013 5:13:02 GMT
Superb! Well done..
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nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 18, 2013 9:37:23 GMT
Thanks both. The oven appears now to be hardening up nicely, I had pushed my finger into the crack in the porch to close it up a bit and I now can't easily compact this any more which is a good sign. No more cracks yet but I haven't put any real heat into it. 25 tea lights at a time appears to lift the internal temperature to 30deg, and the out side to low 20's (cold was around 16 I think). I think I'm going to leave the brick/clay gap for the minute until after a few fires. It'll be easier to fill if it shrinks back a bit more. I also have a few spare oven floor bricks that I might add to either side to the entrance to protect the clay.
Have now started shopping around for a seasoned wood delivery (also got plenty of crap wood to burn for curing fires) and a peel.
(from other thread). Terry, I thought that vermiculite brick thread was really good. Might use that technique to make bricks to line the BBQ thats going next to the wfo (use the wfo to cure them instead of a kiln). I'm also interested in building a rocket stove as garage heating.
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ringo
valid member
Posts: 75
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Post by ringo on Jun 18, 2013 19:46:36 GMT
Great build nixie - looking good As I'm 'borrowing' your floor design (by accident ) but using thick quarry tiles instead, can I ask what cement you laid your storage heater blocks on then what did you use for the firebricks? I've bought a couple of tubs of fire cement but not sure if I've got enough Cheers
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nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 19, 2013 9:47:34 GMT
Hi Ringo,
The storage heater blocks are bedded on sharp sand. There is a very thin bit of normal premix around the edge, this was more to keep the sand in though while I worked on the oven. The firebricks are bedded onto the storage blocks using the same clay/sand mixture that the dome is made from. If I was doing this again I think I'd put less sand under the storage blocks and use some thin bits of insulation to raise them closer to the arch floor height and then use a thin layer of clay slip between storage blocks and fire bricks.
Cheers,
Aaron
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Post by rivergirl on Jun 19, 2013 14:10:21 GMT
Nixie The oven looks really good. Of course the main problem with Clay ovens is shrinkage when curing the clay. On my own clay builds apart from general cracks appearing on the dome (I think I didn't add enough sand to a pure clay when donning the wellies), I have also had separation from the clay/brick arch area. I think this is due to the clay bricks ....already being dry, take most of the heat when starting the curing fires. The clay is naturally initially saturated with water so during the curing process, this junction of raw clay meeting kiln dried clay is going to act against each other?......On my next Clay build I will soak the brick arch in water when I start my little curing fires. Hopefully some of the more experienced Clay oven builders will see this and give advice. I wish I had realised about the shrinkage when I made my first oven opening..... I formed it around the chunk of wood that I was using as the door and went away and left it to dry.................... It took quite a bit of chipping to get the door out !!! My next build will definitely have a brick arch doorway, it seems to be less susceptible to knocks and gouges.
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Post by bookemdanno on Jun 20, 2013 5:57:28 GMT
do you think painting on a clay slip/slurry onto dampened off bricks before building up the clay to them may help?
also, what about making the brick arch more of an integrated part of the oven, you know, like the brick dome builders? rather than building up to the arch.
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nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 20, 2013 9:35:03 GMT
do you think painting on a clay slip/slurry onto dampened off bricks before building up the clay to them may help? No don't think so, will put an updated pic up soon however the main problem is shrinking back towards the dome from the arch,not shrinking inwards (though it is doing this too). also, what about making the brick arch more of an integrated part of the oven, you know, like the brick dome builders? rather than building up to the arch. You mean make the whole parch -> porch -> oven from brick. Suspect this may help yes, also makes the inside of the tunnel a bit more robust. If I was starting again I think I'd do this and make the arch 2 bricks deep. I think though you'd have to use fire cement like the brick oven builders as the brick work would be exposed to more heat. Also the choice of brick would be important for the same reason.
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nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 23, 2013 11:46:12 GMT
So had two burns this weekend. Think I might have gone too big with them though as lots of cracks! Whoops. Photos to follow when uploaded. First burn was couple of hundred inside with 90deg on the outside top. 2nd burn hit 500 at top of dome and 170ish on the outside! Lots of steam last night.
Had a weird think last night where there was no oxygen getting to the back so the flames would die, any idea how to deal with this. Suspect its down to how the fire was set.
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Post by cannyfradock on Jun 23, 2013 14:14:36 GMT
Nixie
It's difficult to comment on the cracks as a lot depends on your clay mix and how slowly you carry out your curing process. Just try to take it steady and fill the cracks with fresh cob once the oven has cooled.
If the oven is built to the recommended formula of (dome height = half the diameter of the oven hearth and the entrance height = 63% of dome height)...or in that ballpark figure, then the oven (once there is a bit of heat in it) should draw the cold air in through the lower part of the entrance and draw it around the dome where the "new" air is expanded and "spent" and exit at the top of the arch. The correct equation of the oven measurements makes this process happen more efficiently....
Terry
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nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 24, 2013 9:32:04 GMT
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nixie
WFO Team Player
Posts: 144
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Post by nixie on Jun 24, 2013 9:33:28 GMT
If the oven is built to the recommended formula of (dome height = half the diameter of the oven hearth and the entrance height = 63% of dome height)...or in that ballpark figure, then the oven (once there is a bit of heat in it) should draw the cold air in through the lower part of the entrance and draw it around the dome where the "new" air is expanded and "spent" and exit at the top of the arch. The correct equation of the oven measurements makes this process happen more efficiently.... Oven is built to those ratios, going to check tonight that the opening hasn't shrunk in loads. I think it could well have been that I was drying wood in the entrance and it caught fire. Suspect having a fire in the entrance then stopped the proper flow of air.
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Post by cannyfradock on Jun 24, 2013 20:19:35 GMT
Nixie
I really wish I could come up with a simple solution.......but I can't. I have suggested fixing the cracks when the oven has cooled down, but maybe.....and it's only just another suggestion....it maybe worth making up a "slip" of clay (soaked in water so it becomes soft) mixed with very fine sand ...and water to make a "slurry" consistency and pour into the cracks while still warm.....and open....even if it means cutting away part of the cracked area so as the slurry can fill the crack......when the oven dome eventually totally cool's, this may seal the gap.
Clay ovens sometimes don't crack.....but more than often do. Please don't get too disheartened.....The first time I saw a Clay oven was at the Abergavenny food festival. A chap called Richard Scadding was there with his "Earth oven"....churning out pizza after pizza for the whole 2 day event (he's there every year)....his "Earth" (clay oven) had a few vertical cracks and a horizontal crack that you could park your car in!!.......the oven still worked....and worked well and he had a never ending queue for the whole 2 days churning out 90 second pizzas at £4 or £5 a throw....and in all honesty, they tasted really good.
Stick with it....and try this and that to fix the cracks ......then once you're happy that the clay has dried......fire the thing up and try it.
Terry
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