Permsteading.com

Hi all,

I just discovered RMHs recently and I'm now chomping at the bit to replace my home's woodstove with one of these. But I have questions! So many questions!

Matt's castable burn chamber seemed like a great way to go, especially since I feel pretty comfortable working with cement / casting (definitely more so than I feel with brickwork!). So I was wondering: is there a reason that the burn chamber and riser are cast separately? Seems like it would be easy enough to do and give a better product because the transition from burn chamber to riser would be entirely seamless...

What I was thinking of doing was using the excellent homemade refractory cement described at Backyard Metal Casting (http://www.backyardmetalcasting.com/refractories.html -- 4-5 cu ft. or thereabouts work out to roughly $60-70, which is quite a bargain compared to commercial products) and using sonotubes and plywood to build a form for a one-piece burn chamber + riser. Then throw cob around it and a 55 gallon drum on top of it. Any reason that shouldn't work?

Hey NY!

Welcome to the nicest bunch of folks you'll ever meet! (and I'm here, too)

I was wondering the same thing about casting the burn chamber and the riser together when I started and I know I've seen other posts about people asking the same question. I think the conclusion is that you could, but the refractory mix is pretty fragile and it would be quite hard to move without breaking that heat riser off. What's more, down the line if your heat riser degrades or crumbles it's much easier to cast a new one if you have some sort of easy way to interface the two. If you do decide to go that route, maybe make sure your inner pipe on the riser extends down into your core so you have the capability of casting a new one onto it in the future if need be.

I have also heard that Matt made a backyard refractory core last year and I seem to recall that it is holding up okay. He'll be back online soon and is probably the best to give advice about this. Keep in mind, I don't think I have $60 or $70 in my clay/vermiculite core that Matt uses. The best thing to do though is just jump in and try it. These things are very forgiving and easy to modify!

Most of the Guys cast their core outside and when moved it into place in the house. The weight was an issue as well as how fragile the 2 would be. If you cast it in place, and you are not worried about removing the bottom of the mold then I don't see much problem. If you want to lift it to remove the mold it may be pretty heavy with the riser cast in place. That's my only thought.

The manufacturing nerd in me wants to remind you that if you choose to cast a one piece unit, be sure to have good support for the riser portion of the moldbox. Metal straps or dimensional lumber used perpendicular to the seam on three sides, with an angle support from the feed end will help to prevent a mishap.

Those are very good points. I believe the refactory mixture described at Backyard Metal Casting should be a little tougher than the clay/perlite/furnace cement mixture that Matt uses... but there's only one way to find out! I'll try casting a sample and subjecting it to some light abuse...

The weight definitely could be an issue. In my rough estimate the two parts together would weigh 150-200 lbs. I guess a 2 part design might be best.

Clay + vermiculite or clay + perlite would definitely be much cheaper (especially because I have an excellent source of clay on my property). I was comparing the refractory mixture to commercial refractory cements, which would run closer to $400 for the same volume. More importantly, I don't mind spending $60-70 on this project.

I think some experiments are in order!

PS: I will definitely (over)build the mold, especially if I'm going the one-piece route. Breakouts are no fun!

let me know what u use for your mix and I am going to cast one also and test it for psi

I've built all of my cook stoves as single units. I build a housing out of the HVAC pipe most use in the bench. I can move it around with a hand truck, but they do get pretty heavy.