by hpmer » Sun Mar 01, 2015 9:26 pm
Yes, the 1:1 ratio is by volume, but you should test it with your materials to see how it holds up, and even make some samples with different ratios some using more ash, some less to see what works the best.
Hopefully your ash has not been subject to rain and the elements as that is said to take away some of the properties that make it work so well.
I use the waterlogged clay as my unit to add the unit(s) of ash to, although if you have more of a clay slip you may want to let it sit for a while. Adding enough water to make a clay slip makes it easier to get the roots and rocks out, but will affect the ratios. If I had a slip, I would let it sit until there was a layer of clear water on top, then pour it off and use what remains as my clay unit. You'll want to make sure to mix it back up because if you made a slip the sands and heavier items will settle at the bottom and clay on top and you want it mixed back up.
Just be sure whatever method you use you are consistent so your final product won't have big variations in layers or sections. Depending on how much ash you are using you'll probably end up adding more water to make it workable. And it will shrink some when it dries, and will likely crack a bit if you don't add some sort of fiber to the mix (and even with fiber it will likely crack some).
I recently wrote a post called "Sap Warmer Rocket Stove Made from Ash and Clay" describing a recent build of mine using this mix and included pictures so you might check that one out.