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Post by lovepizza on Apr 10, 2016 20:45:04 GMT
It looks good doesn't it........2 hours later I ripped it down as the doorway dropped and cracked badly. I suspect I didn't leave enough drying time before removing the sand former. Lesson learned....be patient!!! Can the sand stay in overnight (covered with a tarpaulin) without causing issues? I have now out the clay in polythene bags. Will it stay moist for a couple of days whilst I work up the enthusiasm to again??     |
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Post by downunderdave on Apr 11, 2016 1:37:45 GMT
Did you mix sand with the clay? The structure should be self supporting and able to stand on its own. Maybe your mix was over wet. If it dries rapidly expect it to shrink against the sand mould and get lots of cracks on the outside. You can keep the clay in the same state wrapped in plastic indefinitely provided it is sealed well.
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Post by lovepizza on Apr 12, 2016 5:03:28 GMT
Hi Dave,
Yes, i used sand and powdered clay ( at 3:1 ratio by dry weight as read on another post).
I honestly think I was too impatient. I started digging out of the sand about 2 hours after i had finished rather than the 4 hour minimum recommended. The back of the structure held fine amd was dry to touch. It was the weakest point (the opening) that started to sink. I did prop the door up for a while with some celotex but once the structure started moving south it seemed doomed
Rather than having sleepless nights wondering if it would fail at the first full firing, I decided to pull it down and start again.
Learned my lesson, waiting 4-6 hours next time.
Stuart
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Post by downunderdave on Apr 12, 2016 21:30:53 GMT
Hi Dave, Yes, i used sand and powdered clay ( at 3:1 ratio by dry weight as read on another post). I honestly think I was too impatient. I started digging out of the sand about 2 hours after i had finished rather than the 4 hour minimum recommended. The back of the structure held fine amd was dry to touch. It was the weakest point (the opening) that started to sink. I did prop the door up for a while with some celotex but once the structure started moving south it seemed doomed Rather than having sleepless nights wondering if it would fail at the first full firing, I decided to pull it down and start again. Learned my lesson, waiting 4-6 hours next time. Stuart The drying of clay depends on a combination of temperature, air movement and humidity so it's impossible to give you a time as these all vary, but as the clay dries it shrinks. Wait until it's cheese hard i.e. you can't make a dent in the clay when pushed gently with your finger. If you have made the top of the oven mouth arch semi circular it will be self supporting. If it's flatter you are more likely to have problems. |
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Post by lovepizza on Apr 13, 2016 6:58:57 GMT
Thanks again Dave. I kept it under a tarp last night and it is still very soft to touch so no cracks....Yippee! Today should be a good drying day so probably start digging out the sand a lunchtime..I might even dig out the front and light a little fire just to put a crust on the inside front before going ahead with the full excavation. Here it is at the moment. I have keyed the surface to take a vermiculite layer when i have fully fired the oven (if that doesn't work I will resort to chicken wire).. Wish me luck...  |
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