I'm going to post this on the Cob section as well because I need a quick answer. I am getting ready to start cobbing my bench for my rocket mass heater. I found a source of clay dirt and made sure it had a decent level of clay by doing the usual quick test of wetting it rolling it into a snake and bending it into a circle which worked with no breaks or cracks so I am assuming I have a decent amount of clay in the dirt. I made a few test bricks to determine the correct ration of clay to sand using 1:1, 1:1.5, and 1:2 for dirt to sand. I've let them sit to dry inside my house for the last 3 days and then today I tested them by dropping them from about 4 feet onto concrete. The problem is that they all broke into at least 3-4 pieces. The 1:1.5 seems to do better then the other two but this still isn't the most encouraging sign. Is this ok with how it broke given how I tested it or is this no good for making the bench? Please any quick feedback would be greatly appreciated since I really need to start construction soon with how cold it is getting outside.
You won't be dropping your bench onto concrete. You won't be dropping concrete onto your bench either. You are over doing it, in my humble opinion. Use your best mix, make your bench. Your finish coat should have natural fiber (straw) which adds further to its tensile strength and bump resistance.
The cob is also going to do better as it's exposed to the long drying time and heat from firing your stove, as opposed to air drying.
Best wishes with your build.
posted 5 years ago
Thanks. I was able to make the cob and it seems to be working out pretty good so far. I'll post when I'm all done with the build.
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