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Post by navylark on Aug 3, 2012 5:58:11 GMT
Hi there
I am about to start an oven project, the base is nearly finished. My question
Clay out brick, what are the advantages of each.
At first look clay looks easier to build, faster and cheaper.
Would like your opinions
Cheers Nick
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Post by faz on Aug 3, 2012 9:21:22 GMT
I think clay is cheaper if you have a local source of clay, even cheaper if you can dig it out of your own garden! I have never built a clay oven, but from looking at people's experiences on here, it looks like they tend to be more of a temporary structure than brick, and can be prone to cracking whilst drying. On the plus side it is possible to put one together quickly and cheaply, and if it does go wrong you can add water, mush it up, and start again!! There is also no need for cutting like there is for firebricks.
If you're concerned about environmental impact, then the fact that the raw materials aren't fired like firebricks are during their manufacture certainly makes it a 'greener' option.
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Post by turkey on Aug 3, 2012 9:55:16 GMT
I feel like a broken record but I was originally going to make a clay oven, and I was inspired by this blog fornoeconomico.blogspot.co.uk/His mission statement is which to me sounded ideal, I am sure you can use different clay to the fireclay he uses, I am sure most serious clay suppliers could advise you on what they sell that should be usable, I think a bit of grog as per this build would really help with shrinkage and cracks which really are par for the course with any oven really. If you do go clay and want it to last without a yearly service you will need to consider a housing of some sort or serious waterproofing which might go against the natural feel of clay.... decisions decisions  |
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Post by navylark on Aug 3, 2012 10:30:45 GMT
Thanks for the feedback, I have just found a local supplierwith 1/2 price clay which has been on the shelf for a while - winner. £10 for 25Kg, which I think is a good price.
Turkey
Thanks for the Blog, I do like his mission statment and it does replicate my kind of thinking. I bake bread 3 times a week and if one of these is done in the Clay Oven that would be a good achievement. I've yet to look in the forum for water proofing but i did think about using Lime render, any thoughts.
I've only been on the forum for a couple of days and I am learning so much before i start the oven build.
Cheers Nick
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Post by turkey on Aug 3, 2012 16:07:36 GMT
Hi Nick,
Lime render on its own will not be waterproof I don't think. In my build I am using a lime and cement render with Wickes waterproofer (how well it work I have no idea).
You might be able to get some additive to assist or look at K-Rend which is not used much over here but is supposed to be fully waterproof (silicone based).
Fully waterproof is hard to achieve, water resistant is probably easier and if used on a weekly basis then the heat from the fires might be sufficient.
Decent masonry paint should do a good job of waterproofing the oven also, quite a few floks use this as the top layer to fend off the dreaded rain.
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Post by rivergirl on Aug 3, 2012 19:07:05 GMT
mines clay and I love it until this year when we built a quick roof we just used to tarp it , we cook loads of stuff in it . Its perfect for casseroles and slow bakes, drying veggies and wood !!! still have not made a pizza though .................................................. a good buy with the clay !!!! what are you doing for the base  |
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Post by cannyfradock on Aug 4, 2012 8:00:48 GMT
Nick If you are going down the clay oven route you may want to think twice about buying clay at £10 for 25kg. I haven't built a clay oven but I think you may need about 250 or 300kg for a build?. I have mentioned before that I have tried sourcing clay ....and found a local turf/lawn supplier selling clay at £12 per ton. The stuff that gets dug out from trench work on building sites can also be OK for a clay build....perhaps for free if you talk to the site agent. If I had to waterproof a clay dome I would cover the last clay coat with a couple of coats of lime render, then a final coat of normal render with a waterproofing agent added. The best option I think for protecting a clay oven is to put some type of roof on it......however simple. Here's an example of a simple roof....  Terry |
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Post by navylark on Aug 4, 2012 9:25:35 GMT
Terry
300kg, seems an awful lot. From the blog that faz posted he used 75kg. That it's where I got my estimate from.
Nick
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Post by faz on Aug 4, 2012 10:50:59 GMT
Hi Nick.
My build was a brick oven and the clay was for making the homebrew mortar. You'll need much more for a clay oven.
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Post by cannyfradock on Aug 4, 2012 11:17:20 GMT
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Post by rivergirl on Aug 4, 2012 11:29:25 GMT
I think I used about 300 kilos if I build another one I would do what terry suggests.
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Post by turkey on Aug 4, 2012 16:28:44 GMT
its worth pointing out you usually mix the clay 50:50 with grog or sand. The blog I linked used 75kg of clay and 75kg of grog, also the clay he used was powdered (dry) so cannot be compared to wet (ready to use) clay like ball clay or similar from a potters.
most folks doing a clay oven have dug the clay so they have no idea how much in weight they used, and its often already sandy so they add less additional aggregate to it.
you can use ball clay or terracotta clay but if buying wet it will be harder to mix (puddle) but is a good bit of messy family fun if you have kids, but as mentioned you would need more of it to start with.
does your local clay place sell powdered clay? And do they sell grog, if not sharp sand will probably do the trick, it depends on how high tech or how earthy you want to go.
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Post by navylark on Aug 4, 2012 17:50:54 GMT
Turkey
Thanks for clarifying, my next question was going to be about the difference between dry and ball clay. Sorry for mis quoting in my previous post. For the grog I was thinking about crushed thermo light blocks. Any opinions?
will have to re think the ball clay
Cheers nick
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Post by turkey on Aug 5, 2012 9:10:49 GMT
ahh good question, first I am not a clay expert but the difference is simple.
dry clay is dry, like bagged grit, you add water to it and it turns into moldable clay as you usually think (wet). This way a 25kg bag is say 40kg (total guess don't use for estimations)of wet clay when you come to use it as you are not transporting water in the clay, it will also not dry out in the warehouse etc...
ball clay is simply the bog standard clay you would have used I school, its the cheapest and comes both wet and dry as far as I know,
re thermolite blocks as grog, I think this is probably bad, these blocks are a mix of ash and cement with lots of tiny air bubbles to give it insulating properties. If you crush it you will get cement and ash powder and this probably won't help the clay, plus due to the high air content its probably an expensive way to get the powder.
if doing on the very cheap then sharp sand from wicked would help if no real grog is used. This will bulk the mix up and also help combat cracking as it dries which is very common for clay builds.
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Post by bighairyal on Aug 14, 2012 16:59:07 GMT
Bit late to this party, sorry! I'm hearing talk of 'waterproofing' clay ovens, and my alarm bells are ringing loudly - as it's not a good idea. A cob or clay oven is meant to be fully breathable, such that any moisture released during i.e. baking bread that is absorbed by the clay, can pass through and evaporate from the outside of the oven. If you waterproof the final render layer, this will be prevented and your clay will eventually become soggy and collapse. I have to admit this is not based in experience, but rather from reading the following (and rather splendid) book, which I can recommend heartily to anyone considering building a clay oven: www.amazon.co.uk/Build-Your-Own-Earth-Oven/dp/096798467X/ref=sr_1_1?ie=UTF8&qid=1344963455&sr=8-1If you want to 'waterproof' a clay oven, then you need to build something over the top of it to keep the rain off |
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