Thomas Tipton wrote:I was interested in hearing more about an 8" riser.
Unfortunately the original company mentioned in this post went out of business. The company that bought them out would make an 8” riser if requested but there would be a $1000 mold fee up front, so unless a lot of people organized a group buy for 8” risers it would be cost prohibitive.
Thanks Brian, I have been planning on making a riser out of shredded ceramic fiber using a mold constructed from a 48" length of 8" Sonotube and a 48" length of 12" Sonotube. I was going to saturate the fiber with Sodium Silicate, then pack it into the mold and cure it with carbon dioxide. Probably by using a vacuum pump and CO'2 cylinders.
Hopefully, when it is set, I would be able to slide it out of the Sonotube and then coat it inside and out with 3000 degree refractory cement. This would give it a "Hot Face" on the inner surface, and the application on the outside just to give it added strength and rigidity.
Any idea if this has been tried before? To what degree of success?
Brian James wrote:Unfortunately the original company mentioned in this post went out of business. The company that bought them out would make an 8” riser if requested but there would be a $1000 mold fee up front, so unless a lot of people organized a group buy for 8” risers it would be cost prohibitive.
I'd imagine that's not a viable option anymore. You can use ceramic fiber blanket and a castable refractory cement like satanite, mizzou, or similar. They also have hardeners like ITC-100 High Temperature Ceramic Coating. It looks like you can get it on Amazon nowadays. If you want something freestanding without using a bunch or refractory or fire bricks, you could use nichrome wire on the outside to hold the blanket together, then apply a coating to the inside to seal it up so the combustion gasses stay inside the tube. Best practice will depend on your exact goals and design. My experience is with backyard metal casting foundries, so going this path may not be great for all rocket mass heater designs.
The vacuum formed risers were considered the best riser of their day.
Cost and availability was always a problem.
Shipping them safely was iffy as well.
I never heard any bad reports back from those that did purchase them.
Now, I use and recommend creating a five minute riser made with Morgan Super wool .
Cost is low, even with shipping.
Some safety concerns about breathing this after it has been heated over 1400F (Riser temps are known to be 1800-2000F)
However wearing a standard facemask or respirator a "used" 5 minute riser can be safely handled during a rebuild.
Prier to heating, Morgan super wool is a pleasure to work with.
Risers can also be hand built cheaply using forms with a fireclay and peralite mix .
Heavy firebrick riser can be wrapped with superwool to insulate it.
High temp (2500F) + insulated firebricks also make a fine riser.
Watch for a soon to be available book by Paul Wheaton and Uncle Mud.
It talks in depth about different design risers and riser construction.
As well as all aspects of RMH design.