So I LOVE the look of cob! So magical! I decided I was going to experiment to get that look in a northern climate with cheap materials. The attached picture is a picture of soil cement near my house, as a water dam. Notice how it is crumbling. This was placed there in mid-summer. You'll see some of it is a little lighter because I tried covering it with a painted layer of plaster. Didn't work. I tried changing my mix by adding sand. Didn't help. I think with added sand it crumbled faster. I wanted to try putting an oil on top to try and repel the water, but I ran out of time because I figured I'd need it to be dry first. Still, I know someone here who has a cob oven. They oil it and tarp it and have a cover over it and still had an accident where it started to melt.
I posted on this subject before here and what I eventually discovered online is that there are artists who make a mixture out of cement, paper, paint, and earth (or something like that) and are able to make it waterproof. Thus, the trick might actually been in the paint, not the cement (which does make it worthless for cob ovens). I will probably begin experimenting on this again in spring.
Sam Munson wrote:Hey guys, im very new to construction with COB, and was just wondering, if building an outdoor Cob Kiln/Pizza oven, would it be a viable option to put a small amount of cement mix in the outer layer of cob, to water proof the outside
ement is NOT waterproof. Exactly the opposite. It's porous, and will soak UP water..