Home Brew Clay

[nordberg]

I understand it's possible to make a suitable clay for a clay dome oven using sand and fire clay? Is this correct and if so, what ratio clay to sand?

Many thanks,
Matt

[mikeywills]

I'm sure someone more experienced will be along shortly, as far as I know the mix is 2 parts sand to one part clay. It doesn't have to be fire clay though normal clay will suffice to make a cob/clay oven. I'm planning on digging down over the allotment to get my clay.

There are a number of really good examples on the cob oven board which show you the mixture. I know some use straw or woodshavings for insulation in the second layer.

I was wondering if you could insulate between these layers with ceramic insulation or whether these need to be attached to each other for strength and durability.

Sorry to hijack your thread nordberg

[turkey]

the only build I have seen with fireclay for the dome used 1:1 fireclay and grog, how that relates to sand I am mot sure and different sand types would affect the mix, best bet would be to test it by making a few tiles and measuring shrinkage and its physical properties.

in the clay mix thread in this section I linked to a site with such a build, it details how he tested his mix etc..

mike, if using commercial clay I would not use straw for the main build (called adobe I tjink) , I would also say man made insulation would probably better, you could use vermiculite mixed with a clay slip rather than cement for vermicrete I suppose.

the natural insulation and traditional methods would work but I am not sure it fits, personal choice I guess.

[mikeywills]

I love this site, but it really widens your options rather than narrows them.

I totally understand what you mean about mixing methods, I'm planning on building an adobe inner course as I feel confident I can achieve this more easily than a brick pompeii oven in the time.

I just wondered whether the ceramic insulation would improve the insulation of the oven more than a cob and straw outer layer, or is this better achieved by mixing the vermiculite with the clay? I didn't know that was possible.

I'm conscious that having got the oven upto temperature the tight wad in me would want to make the most of that heat with bread and casseroles.

My daughter is also desperate to decorate the outside with a ceramic mosaic gecko, so you'd be unlikely to be aware the abobe oven was there at all.

[mikeywills]

Found this page on a general search looking for renders suitable for adobe.

www.buildingconservation.com/articles/earth/earth.htm

It mentions why abode walls crack and how to avoid it, which I thought was quite fascinating. As a complete novice to this it certainly cleared up some confusion for me why you use certain mixes.

[cannyfradock]

Hi Matt.....another interesting thread that may go off into another tangent.

I also use 2 parts sand to 1 part Clay (and water). Again....normal clay found underneath the top soil is good enough. You can carry out the "Jam jar" test to see how pure your clay is by putting a lump of mud/clay in a large jam jar, then fill the jar 3/4 full of water. Shake the jar until all the clay is dispersed within the water, then leave to settle (few days). The sand or and aggregate will sink to the bottom, then the clay will settle, then you will have a layer of silt form on the top. You can then see how much sand to add to give a 2:1 ratio.

Mike...I think Rivergirl has put Mosaics on her Clay oven....not sure how she achieved this.

Terry

n.b...(Mike)...please save that link somewhere as I would like to create a "related links" board soon.

[turkey]

Hi Mikey,

I think this discussion probably needs its own topic, one to keep this thread clean for Matt and also so anyone else looking for that sort of info can find it easier.

with adobe I am not sure how long the oven would last, I think it might be more susceptible to moisture, and usually its not covered in a perminant layer, this is partly to do with cost, partly to do with it being a "green" build so the builder might now want man made items there and also because its quite easy to fix or rebuild parts when its a pure clay structure. Check on the clay forum we have had a couple of rebuilds or face lifts (will have to see the pics).

high tech insulation would work just as good on clay as it would on brick so it really would help keep the heat in, traditional methods work well also but usually are much thicker making a far larger structure.

if you are going to seal the outer of this oven (the mosaic would seal it) then you need to make sure its bone dry first or the water will eventually turn to steam and break out possibly through the mosaic. It is a lovely finish to the oven and quite traditional also.

I suppose the key question is what materials do you want to use and why, you can make the oven out of pretty much anything really and its a totally personal experience so there is no reason you have to go down a pure brick and high tech insulation route, and at the same time a clay oven does not need to be 100% dug up from the garden, high tech materials can be used if you want to.

[nordberg]

Wow - great insight guys, thanks! Lots to think about.... My spade is up the allotment at the minute, but I'll try and pop up there before the weekend and try a few more digs for clay. I'd forgotten the lane at the top of our garden used to have a beck running through it. Could be a good site for clay?!?!

[mikeywills]

Sorry Matt, I didn't mean to hijack your thread, I'm used to a gardening forum where a random discussion meanders around many threads. I'll try and keep my questions topical.