Mud and I are working on a book. This is the part about vermiculite board risers. We strong encourage everybody to share their experiences. We hope that this
thread will grow to ten pages of information about vermiculite board risers.
I did a lot of research on the melting point of vermiculite about ten years ago. My research then suggested that it would melt at 1500 degrees F (100 degrees higher than perlite). I verified this data with several other sources, then I regurgitated “1500” for years. Recently I was challenged and …. I am going to say that the prevailing data has changed … my new research shows numbers between 2000 and 2400. While I am doing my best to be okay with the new numbers, I confess that I am a little suspicious.
Mud says:
I have a six inch riser that is six years old and still looks new. I can’t say that about risers I have built from insulated firebrick or ceramic fiberboard.
I have always avoided vermiculite because the material is so crumbly. But we stock it here for events because so many
rocket mass heater experts like using it.
The general idea is to cut four rectangles and screw them together to make a square tube riser. You must use stainless steel screws - because only stainless steel will cope with the high temps. And just to make sure that there are no leaks at the edges, some builders will wrap the vermiculite with a high temp wool. I have seen others create a steel exoskeleton covering the gaps.
I have never seen vermiculite melt. Nor have I heard of vermiculite melting. But I would still be shy about using it in an 8 inch system. And I just don’t like working with it because of the crumbliness.
Mud says:
I would like to try it in an 8 inch system. I am about 80% certain that it would last more than five years.
Total cost is about $120 to $180 without a wrap.
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