Concrete rocket bell

[2tranceform]

Hello fellow pyros. I have been reading about the stoves here for a while. I am planning to build a rocket bell stove. I am wondering if the walls of the stove can be cast concrete. I am thinking of bricking the firebox. I also planned on using fire clay and or fire caulking to seal the seams. I am looking for input on this idea. Is this safe? Will it fall apart in a few months? Is this just a bad idea?

Thanks for posting up all the great info. I really appreciate it.

[Deleted]

Oct 3, 2012 13:38:54 GMT -8 2tranceform said:

I am wondering if the walls of the stove can be cast concrete.

One needs to prevent spalling, which is a problem especially in structurally dense concrete.
Even dry concrete contains some amount of water, which will evaporate in high heat.
In structurally dense concrete water may cause explosive spalling.

The obvious solution: Break up the structure.
This can be done by adding some not fire resistant fibers (e.g. paper fiber) to the mix.

I have build my rockets with a mix of clay, sand, portland cement and paper pulp.

[2tranceform]

Thanks for the reply karl. That does make sense to allow for movement within the structure.
* Will any expansion joints be needed in addition to the space created by the combustible content? I am planning on casting the stove in multiple pieces. Mainly to save my back.
* Approximate ratios for your mix?
* What type of clay do you use? I have heard of using cat litter, the clay variety).
* What type of sand? River sand or quarry sand (round vs. jagged).

[Deleted]

Oct 5, 2012 6:37:32 GMT -8 2tranceform said:

Thanks
I am planning on casting the stove in multiple pieces. Mainly to save my back.

Good Idea.

* Approximate ratios for your mix?

5 Clay, 2 Sand, 1 Cement.
Paper fiber 1-2% of the dry weight.
It is not desirable to lower the heat transfer to much.
More Sand would make it a bit cheaper.

* What type of clay do you use? ).

As you want to harvest heat in a bell the heat transfer should not be to low.
Clays with an high content of alumina are preferable e.g. kaolin or fire clay.

Properties of clay minerals in German and English.
www.uni-weimar.de/Bauing/bauchemie/Downloads/Vogt_ZJ_2003.pdf

* I have heard of using cat litter, the clay variety).

One can use cat litter as insulation.
I would not recommend bentonite, the clay variety, for other purposes in a stove.

* What type of sand? River sand or quarry sand (round vs. jagged).

Crushed sands will give stronger structures, once hardened.
Rounded sands will give lower viscosity with the same amount of water.

[2tranceform]

Wow, thanks for the great information. I have found fire clay locally along with the sand. I do have a couple more questions about the mix.
* Are the ratios by volume or weight? I do see that the paper is by weight.
* Paper fiber? Is this shredded paper, perlite, vermiculite, or something else?

Since I have this weekend off, I should be able to get things planned out a bit better and possibly post some designs for critique.

[Deleted]

Oct 5, 2012 8:50:59 GMT -8 2tranceform said:

Wow,
* Are the ratios by volume or weight? I do see that the paper is by weight.

It is a bit difficult to measure paper fibers by volume.
For clay, sand and cement it does not make a big difference.

5 Clay, 2 Sand, 1 Cement by volume
are about equal to
5 Clay, 3 Sand, 1 Cement by weight.

* Paper fiber? Is this shredded paper, perlite, vermiculite, or something else?

Cheap toilet paper would be the simplest to dissolve.
Shredded and dissolved paper would do it too.
Not much to save.

The paper fiber is not for insulation, thus no perlite, vermiculite or the like.
The purpose is to let steam escape and to make it harder for cracks to grow.

[2tranceform]

I have been having some trouble finding fire clay in my area. A supplier suggested heat stop 50. Will this stuff make a suitable substitute? Material cost is about $.31/pound.

[2tranceform]

Looking at the MSDS, the heat stop 50 is about 20% Calcium Aluminate Cement, 15% quartz sand, and 65% fire clay by weight. I am thinking about getting this for the mix and add more sand to bring the ratios up to the ratios provided by Karl. Any thoughts on this?

PS. for your viewing pleasure:
www.heatstoprefractorymortar.com/HEAT-STOP-50.pdf