Post by rural on May 19, 2014 20:46:07 GMT -8
During a trip to Home Depot I was looking at Roxul insulation to insulate risers. Roxul is a Canadian company that makes several mineral insulation products. They have batt insulation of various types but what caught my eye is a board insulation. At first, I thought it would be a more solid product, like perlite or vermiculite board, sort of like styrofoam. However, it's more like a really dense batt, almost like felt. It's fairly rigid. There is some give, but definitely rigid enough to make a heat riser. Since my sons have made a hobby of breaking bricks, using a different material for the heat riser would free up enough bricks for a 7"x7" rocket stove core. Joining up four pieces of the stuff seemed much easier than doing something with perlite and slip too. So I bought a package of Roxul "ComfortBoard" which contains 6 2'x4'x1.5" boards for about $50 (Canadian). That's enough to make three risers with some to spare. The 1.5" boards give an insulation value of R6.
The only thing I don't like about the product is that it has a textured pattern on both sides that sticks out somewhere between 1/8" and 1/4". It might provide a bit of turbulence, sort of like many trip-wires, but I have my doubts. In any case, one should probably add a bit to the inside dimensions to make up for extra drag the pattern will cause. I didn't think of this until after cutting the pieces.
And the board cuts very easily with a utility knife. I used a piece of 3/4" plywood as straight-edge and to keep the knife square. It worked fairly well.
The four 8.5" wide pieces were joined with slip made from local clay soil, ash (maybe 15% ash by volume, not enough) and enough water to give a yogurt-like consistency. I used a small paint roller to apply the slip to the parts of the board that needed it. This didn't work very well. My recommendation would be to build a trough so that the boards can be dipped into slip where needed. (I didn't coat the whole boards in slip, just the parts that needed to be connected to neighbouring board or brick.) Getting slip onto the first two boards and placing them was tricky to do alone. A helper would make this task easy. Once in place, twine was wrapped around the boards to keep them tight to one-another while the slip set up. An hour later the twine was removed and the boards didn't budge.
After a couple of 90 minute burns, the slip seems to be holding fine. I suspect the slip is stronger than the boards and that they will be damaged when pulled apart, but we'll see. I'll probably do another burn in the next few days, then pull everything apart so that my sons can have their sandbox back. (Yes, my laboratory is a sandbox.)
I'll post some pictures at some point in the next day or so.
The only thing I don't like about the product is that it has a textured pattern on both sides that sticks out somewhere between 1/8" and 1/4". It might provide a bit of turbulence, sort of like many trip-wires, but I have my doubts. In any case, one should probably add a bit to the inside dimensions to make up for extra drag the pattern will cause. I didn't think of this until after cutting the pieces.
And the board cuts very easily with a utility knife. I used a piece of 3/4" plywood as straight-edge and to keep the knife square. It worked fairly well.
The four 8.5" wide pieces were joined with slip made from local clay soil, ash (maybe 15% ash by volume, not enough) and enough water to give a yogurt-like consistency. I used a small paint roller to apply the slip to the parts of the board that needed it. This didn't work very well. My recommendation would be to build a trough so that the boards can be dipped into slip where needed. (I didn't coat the whole boards in slip, just the parts that needed to be connected to neighbouring board or brick.) Getting slip onto the first two boards and placing them was tricky to do alone. A helper would make this task easy. Once in place, twine was wrapped around the boards to keep them tight to one-another while the slip set up. An hour later the twine was removed and the boards didn't budge.
After a couple of 90 minute burns, the slip seems to be holding fine. I suspect the slip is stronger than the boards and that they will be damaged when pulled apart, but we'll see. I'll probably do another burn in the next few days, then pull everything apart so that my sons can have their sandbox back. (Yes, my laboratory is a sandbox.)
I'll post some pictures at some point in the next day or so.
That ended up in a mess. Little nail size flakes of the stuff everywhere. 