Thor Markussen

Thanks Phil. And yeah, I look forward to see what this little one can do. I'll post an update here when it's finished and I've had a chance to test it a bit!

Hi again folks,

I've been doing a bit more research and now I'm worrying a bit about the shrinkage of the fire clay mortar when it dries. Basically, in the Poelito design I need to make some quite precise casts for the burn chamber and the heat riser. I've attached a photo of each cast. The casts are normally done by making moulds using hard cardboard tubes which are then covered with cellophane. When the mortar (refractory concrete, in the design) has dried, the tubes are removed and/or burned out. But if I'm using a mortar based on fire clay, vermiculite/perlite/pumice and water, I worry that the mortar will shrink so much when drying that it will break? Do you have any ideas about this? Would I not risk that the casts will "implode"/break around the cardboard tubes?

Hope you can help me (and my partner...) with these worries on our quest to a concrete-free tiny rmh!


 

Awesome, just the info I need! Thanks so much, both of you. I think I will try and use as much sand as possible and cast the burn chamber and heat riser with fireclay and crushed firebricks/pumice/perlite depending on what I find. That seems more like a permie solution to me than buying new concrete and refractory grog. Off to the calculations, it is!

Thanks a lot to you also, Thomas - again very useful information! Would you be able to also enlighten me regarding my second question? Am I correct that I lose some heat storage capacity if using semi-refractory grog with less aluminum than refractory grog?

Hi Phil

Thanks a lot for your quick reply! I actually didn't even know that such a thing as fireclay existed! So just to make sure I understand, you mean that I can replace the refractory concrete with fireclay, correct? Thus making a mortar of fireclay and refractory grog. Why would one choose refractory concrete over fireclay anyway?

I'm also looking for possibilities to substitute the refractory grog. I suppose I would be able to just use semi-refractory grog (aluminum content 10-20%) for instance, or even broken down old firebricks? If I understand correctly, what I would lose is a bit of inertia, thus less heat storage, if I'm correct?

Sorry for all these anwers, the world of mass heaters is still just opening to me (and it's very exiting!).

Hi all,

First post here, I've been checking around and I haven't found a post that answers my question, so excuse me if I'm wrong.

I'm starting a construction of a Poelito - a tiny rocket mass heater that is designed for yurts:
https://www.instructables.com/id/Semi-removable-Mass-Stove/

It's a quite ingenious design, with everything fitting inside an oil barrel  - nice when you don't have a lot of space! The basic idea is to make moulds and pour refractory concrete around this, then fill up with sand in the top part. However, the refractory concrete is based on fire cement and I'm wondering if there isn't an alternative to this? Could I potentially use a clay mix of some sort instead of the cement? I guess I would still mix it with refractory chamotte (grog), even though here I would also prefer for instance breaking down old red clay bricks and make a mortar with this.

So basically, does anyone have a suggestion for how to make an alternative to the refractory concrete? Using what can be found second hand/in nature, rather than new products?

Thanks a lot in advance!