I tried dry-stacking a variety of materials and was frustrated with the results. In my ignorance, I blamed the materials, when the real crux of the problem was the number of air leaks in the systems I built. Before I heeded the advice to create a sealed riser, at the very least, I had to use a small fan to force
enough air into the burn chamber to generate the kind of heat I wanted to see. After I sealed the riser and burn chamber properly, two of the three materials I had been playing with worked very well. The third was a
concrete paver and simply too porous to create enough heat, unless I was patient enough for that entire mass to get really warm, which took anywhere from 30 to 120 minutes, depending on conditions.
Once I built a proper, sealed unit, out of suitable materials, I had 500 degrees (F) or more within just a couple of minutes of starting the stove. This was the difference between a rocket stove that I could barely simmer soup on to one that would get a
cast iron pan hot enough to sear meat properly. Also, the amount of smoke coming out of the riser decreased dramatically when I finally had it burning hot enough. Those are my experiences with dry-stacking.