DIY Refractory Cement

Howdy folks... first post here.

I have a rocket stove build in mind and I'm currently just researching materials; specifically, I'm working on the core and riser. Experimental is "okay" for now, as this will be an outdoor build but I really don't like doing things over if i can help it.

I've seen a recipe turn up several times for refractory cement, both on here, and on sites for metal casting/kiln building, etc...

I'm sure this topic has been beat to death, but I've seen several conflicting posts so I thought I'd dedicate a thread to it.

Here is the mix:
1.5 parts Portland Cement
2 parts silica sand
1.5 parts perlite
2 parts fireclay

Everything in this recipe I can find cheap and local.

...that said, I see many posts which warn zealously against using portland cement anywhere in your build. Many use "refractory cement" for the mix. I actually wouldn't be surprised if "refractory cement" simply is a premix of cement, sand, and fireclay.

Perhaps in the bonding process while curing the heat resistance necessary is created?

Anyway, I thought I'd post this to see if any have had success with it. IF it works, it'll be a much cheaper alternative to using insulating firebrick for the whole build.

Thoughts?

What about using Aluminum Oxide instead of Portland cement? like used in firebrick.

Hello,

I am sorry I don't have more time to dedicate to this subject of "homesteading and permaculture arts." I am very interested in it and have a reasonable background in what some would call "fire science" or "wood burning tech."

As a quick "drive by" comment...Please don't confuse "refractory masonry materials" with "refractory insulative materials." They are vastly different in function and form. Most of these "DIY" concocktions that is seen and read about by so many folks are not "refractory cement" or even a related masonry...they are an "insulative mix." OPC (ordinary portland cements) of any form cannot withstand the extremes in thermal flux or high temperatures...A true "refractory masonry mass" be it a brick like form or some pourable mix, is going to take extreme temperatures and last quick a long time before dermal degradation, structural compromise, or other interstitial issues arise.

Really "study" true refractory products, and what they are made of, and also look at the art of building "ceramic wood fired kilns," and traditional masonry heaters (TMH), which RMH are part of. This technology has strong cross over into designing good RMH.

Regards,

j

Refractory cement doesn't have any portland cement in it. Some versions for lower duty may have a small amount of portland, I think for pre-firing strength, but it cannot be a major ingredient.

To clear things up I should say this is for a "rocket mass heater" vs. a "rocket stove" as I had identified in my original post. The same rules apply, but it seems we aren't as zealous about cooking stoves.

Based on the responses I assume that you guys don't feel that the mix identified in the OP is going to cut it in a RMH core? Could it perhaps be used solely for the riser?

Scott Lambeth wrote:To clear things up I should say this is for a "rocket mass heater" vs. a "rocket stove" as I had identified in my original post. The same rules apply, but it seems we aren't as zealous about cooking stoves.

Based on the responses I assume that you guys don't feel that the mix identified in the OP is going to cut it in a RMH core? Could it perhaps be used solely for the riser?

Fire clay and Perlite are fine to use for casting the entire riser tunnel and feed, you do not need to use sand. I have heard of some people using a bit of store bought furnace cement in the mix as well.

Hi Scott,

Remember, there is a great deal of "reinvented wheels" on the internet created by way too many "backyard inventors." This is all good and fun to watch and experiment along with...but they are not, for the most part...experts or teachers of craft and general good practice.

When I try seek knowledge I do my best validate the experience base before I pass on the info...or...I validate that information is "experimental or speculative."

A castable burn chamber... is a great post link to read. Ken's comments are very informative to the nature of refractories. I have seen many "fire clay-perlite" mixes work...and others just degrade and fall apart. With "home made" recipes the outcomes are often only as good as the base materials employed. I (et al that build kilns and/or masonry heaters) do not use OPC of any kind and never where heat is involved....

Regards,

j