#1  
Old 07-05-2010, 10:35 PM
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Location: Perth, Western Australia
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Default Weatherproofing clay?

I have read that clay must be left to "breathe" and you must create a roof for your oven or put it under a tarp in the rain.

Is there any possible way to weatherproof a clay oven igloo dome like the better homes and gardens one here:

Episode 18 - 13 June - Better Homes & Gardens Magazine - Yahoo!7 Lifestyle

I want mine to look a bit like this one (thanks backyardpermaculture for the link)

Part 8 - Fire me up! Portable Pizza Oven
- mine will be on wheels too...

Love this site! can't wait to get started...
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Old 07-06-2010, 06:20 PM
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Default Re: Weatherproofing clay?

Quote:
Originally Posted by wakamole View Post
I have read that clay must be left to "breathe" and you must create a roof for your oven or put it under a tarp in the rain.

Is there any possible way to weatherproof a clay oven igloo dome like the better homes and gardens one here:

Episode 18 - 13 June - Better Homes & Gardens Magazine - Yahoo!7 Lifestyle

I want mine to look a bit like this one (thanks backyardpermaculture for the link)

Part 8 - Fire me up! Portable Pizza Oven
- mine will be on wheels too...

Love this site! can't wait to get started...
In a word, no. However, nothing in the rule book requires covering the oven 24/7 - or at all.

A clay oven will not melt at the first rain fall. It cannot take long term exposure to running water but it's not essential to enclose/weather proof an oven - pretty obviously, since neither of those ovens are enclosed. Long term you will probably end up repairing the exterior - but the beauty of cob is that such repairs are simple.

One of the best solutions I've seen was a temporary roof that the owner put over the oven when it rained and left off otherwise. If you miss a storm it's not a big deal - anything that will destroy an oven in one storm probably will do much more damage to your roof!

You can coat it in lime but not in anything water proof or water resistant. Because they dry at different rates the likelihood is that moisture will get trapped between the clay and the water proofing and that will destroy the cob.

All that said, there is one other thing - you're gonna be baking the clay/cob which is not true of cob houses. I have seen pics of an oven built in a day, fired the next to pizza temps and destroyed the third (it was built for a workshop on building ovens). It took a diamond blade to cut through the thing. My semi-educated guess is that an oven will become much more weather resistant than its building cousins over time. Like brick, it won't be able to tolerate constant moisture but also like brick it will tolerate weathering much better than cob alone. But again, that's an educated guess, not a proven fact.

My theory: if it's gonna be a gully washer, protect the oven with something. Otherwise, don't worry about it.
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Old 07-06-2010, 09:52 PM
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Default Re: Weatherproofing clay?

Thanks Archena
That lets me rest a bit easier - though the outer layer will be insulated with vermicrete which may be more absorbent than the clay...

I like the idea of building something in a weekend with my kids that may last me many years!
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Old 07-07-2010, 07:47 PM
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Default Re: Weatherproofing clay?

I think the bigger issue you will face is not so much water damage but rather the water dampening the insulation, which won't function until it dries out again. You really don't want to have to keep firing up the oven just to dry it out again, and the outside could get dangerously hot too.

I guess it depends on local climate - Perth should be fairly OK through the summer, unlike Brisbane
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Old 07-07-2010, 09:32 PM
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Default Re: Weatherproofing clay?

Thanks Mick
good advice
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Old 07-08-2010, 04:53 AM
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Default Re: Weatherproofing clay?

I missed that. In clay ovens the insulation is usually between two layers of clay. A light clay/sawdust mixture is common.

I'll see if I can find a link somewhere - I actually read that in a book.
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Old 07-08-2010, 03:27 PM
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Default Re: Weatherproofing clay?

True; before I built my oven I looked at the more traditional cob ovens that have the insulation sandwiched between cob layers. This website gives a good rundown. He has had water damage though, and doesn't seem to anticipate a long oven lifetime.

Cheers,
Mick
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Old 07-15-2010, 04:31 AM
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Default Re: Weatherproofing clay?

Quote:
Originally Posted by wakamole View Post
Thanks Archena
That lets me rest a bit easier - though the outer layer will be insulated with vermicrete which may be more absorbent than the clay...

I like the idea of building something in a weekend with my kids that may last me many years!
the vermicrete will be waterproof, so this will keep water out but is not breathable so will hinder drying of the clay, I would do all the drying rituals before adding this.

air dry for as long as you can, then possibly go for using a lamp in it to generate a modest heat, then small fires over a few weeks to slowly drive the moisture out, speed here is not a good idea, once you have it nice and dry you could insulate it with the vemicrete and this will then waterproof the whole thing on the outer crust.
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Old 07-15-2010, 04:52 AM
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Default Re: Weatherproofing clay?

Quote:
the vermicrete will be waterproof, so this will keep water out but is not breathable
Um, I'm afraid I'm somewhat suspicious of that statement? All of the evidence I've come across previously has pointed to the contrary.

Cheers,
Mick
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Old 07-15-2010, 12:11 PM
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Default Re: Weatherproofing clay?

Vermiculite, in garden use, is designed to absorb water. That's what it does. Vermiculite concrete is also soft and breakable. You want to cover this up one way or another.
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