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Post by dodders on Oct 20, 2012 15:25:51 GMT
I finished the sand former using MDF template. This was a few weeks ago. I'm always surprised at how when I try to estimate a volume I'm always wrong, and there's always more to a volume than you'd imagine. More bags of sand needed.... Attachments:
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Post by salilah on Oct 20, 2012 16:55:55 GMT
Very smart!! ours is a bit more - well, "rustic" is perhaps the best word? (lopsided actually)
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Post by cannyfradock on Oct 20, 2012 17:37:57 GMT
Dodders
Love the picture. It shows high tech work with your formers that are not so difficult to follow.
Terry
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Post by rivergirl on Oct 20, 2012 17:56:25 GMT
A lot more techno than my oven!! I just made a huge sandcastle LOL good luck for the finish.
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Post by bhbnnc on Oct 21, 2012 14:27:40 GMT
Wow... That's what I was missing.. Looks great
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Post by dodders on Oct 21, 2012 15:07:09 GMT
Thanks for the comments. Maybe the entrnace is a bit long, but I then realised I shouldn't worry because I can always 'trim' it if that's the case; that's one advantage of a cob build I suppose. Attachments:
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Post by cannyfradock on Oct 22, 2012 17:05:31 GMT
Looking good!!.....long handled pizza peel and.....away to go.
Terry
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Post by dodders on Jan 10, 2013 14:44:55 GMT
Having let it lie dormant for a couple of months under its wooden shelter I took out all the remaining sand today. It's dried out reasonably well, i.e. it's now fairly hard. Just lit a small first fire; so far so good although a small crack or 2 has appeared.
Next I need to put on the outer cob layer and was wondering if using glass mesh/fibre would make this stronger and more durable than using straw in the mix? Roll on the Spring.
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Post by dodders on Jan 10, 2013 14:48:53 GMT
Pic attachment didn't work last time so here goes again. Attachments:
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Post by rivergirl on Jan 10, 2013 15:21:29 GMT
I cannot help with this problem but hopefully someone will be along shortly.
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Post by cannyfradock on Jan 10, 2013 20:10:29 GMT
Dodders
By adding fibres to the second layer of Cob will certainly help with it's own integral strength. The sand gives the initial strength to the clay build. The straw...or fine wood chips gives the thermal value to the 2nd layer. The straw (cut in small pieces) will give the outer clay/cob layer a honeycomb effect which both adds an insulation factor, plus a heat stop which keeps the heat within the cob.
When woodchips are used, the principle is that the woodchips (not sawdust......must be coarser) will create tiny voids and will eventually burn out leaving a honeycomb structure, which acts both as a thermal layer plus a heat stop.
The natural process of drying clay means it will contract on drying so cracking will appear. Clay oven builders parge these cracks up with more clay, but I would mix a slurry of clay, sand and hydrated lime and paint this into the cracks. The addition of lime will help the natural process of expansion and contraction between firings.
The weakest point of a clay build without an entrance arch will be the entrance hole cut from the clay. This would be a good area to incorperate some kind of fibres.
Keep us informed (please) of your progress.
Terry
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Post by dodders on Jan 11, 2013 8:37:48 GMT
Thanks for the detailed reply Canny.
I had wondered about the insulation issue and whether glass mesh would be less effective. Maybe I should just use glass above the entrance , which is where the largest crack (only a few mm) has started to appear. I've no shortage of wood shavings! I did also wonder about glass possibly contaminating the food which would be dangerous bit dismissed that as it would completely sealed in the clay/sand mix.
Not quite sure when I'll be able do the outer layer but will keep you posted. Thanks again.
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Post by turkey on Jan 11, 2013 17:57:19 GMT
Looks great and sounds like you have a great plan,
Not sure glass can contaminate other than directly fall into food as its pretty much inert itself and often used in contact with food assuming its clean when you insert it into the oven.
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Post by limpopomark on Feb 17, 2013 10:00:26 GMT
Hiya dodders
Love the smooth lines on this build. I realise (having pretty much finished...) looking at your oven that having near vertical walls lower down within the oven around the hearth makes moving stuff around/in/out a lot easier... I should probably have made a more steep sided sand form than I did; oh well - next time!
Good luck with the rest if it, and the weather
mark
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Post by dodders on Feb 19, 2013 17:32:02 GMT
At last some dry sunny weather, and a bit of spare time and a helpful son. Next layer has now been plastered over the arch and, folowing Canny's advice, I've incorporated some glass fibre mesh.
Mark, thanks for the positive comments.
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