This is my first attempt at a Rocket Heater so keep in mind I'm very new to this.
I would like to build the burn chamber and riser tube of my RMH using Fire Clay and perlite. Unfortunately, I can't find Fire Clay (Motar Clay) anywhere. I called all the fireplace and stone dealers in my area. I called all the material suppliers and all the places they recommend and no one carries it. There was one place that was willing to special order Fire Clay for me but they said they would only do it when they are ready to place an order with that supplier and after they order it would still take 4-6 weeks for delivery. However, they recommended a product they carry as a substitute. Alsey Hi-Cast 45 Refractory Castable.
I was hoping to get some input from the community on if this product to determine if it would make a good substitute for the traditional Fire Clay/perlite mix. If not, how could I modify it to make it work.
Description: Dry, hydraulic setting, high duty refractory castable. HI-CAST 45 is a general purpose 2700°F castable effective for most standard operating service conditions.
TYPICAL TEST DATA -- PHYSICAL PROPERTIES ASTM C-24 P.C.E............................................................................... 31-31½
Temperature Equivalent (melting), °F ......................3061-3090
Service Temperature (max. recommended), °F................. 2700
ASTM C-20 after 2500°F
Apparent Porosity, %.......................................................... 25.9
Apparent Specific Gravity g/cc ........................................... 2.71
Bulk Density lb/ft3
ASTM C-113 Schedule B % linear
Reheat Change at 2550°F ..................................................... 2.2
Application: Recommended water content is 9-12%. [2.5-3.5 US Quarts / 55lb bag.] Actual water content may vary depending on job site conditions. Coverage 55lb sack = .44ft3 Stir dry mix thoroughly and add the correct ratio of water. Return unused portion to the bag. To avoid moisture absorption, store HI-CAST 45 in a cool dry place. Under normal atmospheric conditions, set will occur 8 to 10 hours after HI-CAST 45 is mixed. Heat can usually be applied after 24 hours; however, starting temperature must be held below the boiling point of water to avoid the formation of steam which will result in excessive cracking, spalling and lower strength.
The two main chemicals in the mix are Silica and Alumina. As I understand (in general terms), the Silica and Alumina work together to create the "Fire Rating" and "bonding agent" for the mix. I believe I could this mix in it's raw form to case the burn chamber and riser tube for my RMH. However, I don't believe this mix will have the insulating properties that are necessary for the burn chamber and riser tube. Is that correct?
If so, what other materials could I add to this mix to get the insulation properties needed? If I add perlite to this mix at a 50/50 ratio, do you think it would cause the mix to be too brittle? Are there any other readily available materials I could add to the mix to increase the "bonding properties"?
As of right now, the Alsey Hi-Cast is the only option to get my project started this year. They charge $48 for the 55# pound bad.
That's not a bad price for refractory. Way more than fireclay but should be more durable than the FC mix Your going to want to experiment. Try a small batch at 50/50 then try a batch at 70/30 I think a 50/50 mix might be to fragile in the feed tube but be fine in the burn tunnel and riser. The fireclay mix is known for wear issues in the feed tube (trying to push wood down) When casting a core you should be able to vary the amount of perlite, using a refractory heavy mix at the feed tube end and then add more perlite as you form the burn tunnel . The riser can be cast with a "fragile mix " heavy on perlite.
I second everything Thomas said. Where I am (upstate NY) refractory costs 4 or 5 times what fireclay costs, but if you need to ship the fireclay, it's pretty much a wash.
I would suggest making a richer refractory mix for the inner surfaces of the feed tube and burn tunnel, and surrounding that with a highly insulative mix. The riser can be mostly perlite with just enough refractory to hold it together (make test bricks with various ratios). You would probably want a sheetmetal (stovepipe or ductwork) outer shell for the riser to strengthen the unit and make it easy to handle for installation or maintenance.
thomas rubino wrote:That's not a bad price for refractory. Way more than fireclay but should be more durable than the FC mix Your going to want to experiment. Try a small batch at 50/50 then try a batch at 70/30 I think a 50/50 mix might be to fragile in the feed tube but be fine in the burn tunnel and riser. The fireclay mix is known for wear issues in the feed tube (trying to push wood down) When casting a core you should be able to vary the amount of perlite, using a refractory heavy mix at the feed tube end and then add more perlite as you form the burn tunnel . The riser can be cast with a "fragile mix " heavy on perlite.
I went out and bought a bag of the Hi-Cast and perlite last night. I made bricks of a 50/50 mix and a 75/25 mix to test them out. I want to let them dry for 48 hours before handling them. Thanks for the advise.
Glenn Herbert wrote:I would suggest making a richer refractory mix for the inner surfaces of the feed tube and burn tunnel, and surrounding that with a highly insulative mix.
That sounds like a good idea.
Glenn Herbert wrote:The riser can be mostly perlite with just enough refractory to hold it together (make test bricks with various ratios).
I'm going to make a 25/75 refactory/perlite mix tonight for testing.
#1 - 75/25 refractory to perlite
#2 - 50/50 refractory to perlite
#3 - 25/75 refractory to perlite
#1 was extremely strong and had the most mass. In the mold I used, this mix ended up to be 1.5" thick. I couldn't break it by setting the brick half way over the edge of the table and using all my weight (230#) to break the brick.
#2 was strong and ended up 1.25" thick. I was able to break this brick using the method above. But I had to put all my weight on the brick.
#3 was weak and ended up 1" thick. I was able to break the brick in half with my bare hands without much effort. I also used too much water in this mix so there was a thin layer of refractory settled on the bottom of the brick.
My original plan was to cast the base and riser tube as one unit. But after doing some general estimating, I think the entire mass will be too heavy. So I will cast them separately.
For the riser, I plan on using a 40/60 refractory/perlite mix. For the base (wood feed and burn chamber) I plan on using a variation of 25/75 to 75/25 refractory to perlite mix in the different zones of the base.