Hi everyone, I have a question about waterproofing a clay oven, trying to avoid building a roof (it would be my first attempt at carpentry and I dread it...) I know what everybody say about clay ovens needing to breathe but I think: what would happen if I had it rendered with normal cement plaster? When I fire the oven, even for hours, I don't see steam coming out of the outer layer so I think the chances of the render cracking (or exploding) would be minimal. At the moment I am covering the oven with a tarpaulin and it has been ok, but it quite an eye sore. If not possible, would anyone have any suggestions about a roof..... Thanks for your thoughts, Stefano
This is just a suggestion from a Pompeii oven builder. As clay ovens tend to move a lot with the extremities of the temperatures and are more prone to cracking, you would need to apply a layer of something before applying a waterproof render coat. Vermecrete would be OK but the vermiculite that is normally sold would be too coarse for your needs. You can buy a very fine vermiculite and if you mixed this(100ltr bag) with half a bag of cement and half a bag of hydrated lime ....and water this would give you a sticky mix which could be laid quite thin but still be pliable enough to take the movement of the clay. You could then apply a waterproof render (preferably in 2 coats with chicken wire sandwiched between the 2 coats......or just buy 2 bags of K-rend and apply the same as the waterproof render.
A roof structure isn't that difficult to do. It depends on how much space you have left on the outside of your oven. If you have no space then you could fix upright 4" X 4"'s to each corner for a base for your roof...or set the 4" X 4"s outside your oven with metposts......lots of options.....
Hi Terry, thanks for your reply. I forgot to say that the oven has already got an insulation layer made with clayslip and sawdust. I think that this is probably already absorbing some of the tension created by the expansion of the thermal layer. In any case Iwill speak to the plasterer that is going to help me out and we will decide. Regarding the roof, I have built the base with breeze blocks on an area already paved with sandstone so the easiest option would be to erect the structure on the four corners of the base. If I placed the posts outside the base then I would have to fix them to the sandstone which I am really not keen to do. Thanks again for you suggestions Stefano
St.Astier do a range of ready to use lime renders with integral waterproofers added. Still in powder form, but none the less, ready to use as you just add a gauged amount of water. Normal integral or paint on waterproofers are not designed for Limes. Limes are no longer any harder to use than cement based products, and supposedly a better suited material for buildings. I'd perhaps think about a fibre blanket, like Rockwool, of some kind, which would have more "give" and act as a shock absorber layer and It would still breathe. Fit a chicken wire mesh over, then flick a slurry coat at the blanket. Let it go off a bit, to crust up, then hit it with the Lime Render!