Building a rocket cook stove - can you help?

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Flannelfoot

Tenderfoot
Apr 15, 2012
84
0
South-west
Hi guys - know anything about Rocket stoves?

I want to make several "Rocket" cooking stoves for cooking meals/boiling water in times of an electricity outage. It is basically a 20-30 liter bucket with an L-shape made of 4" PVC pipe. The remaining cavity is filled with castable, removing the PVC pipe when cured - and cutting away the plastic bucket once fully hardened. Here is a photo of what I'm basically talking about: https://i.ytimg.com/vi/aOZ7gJaqdtQ/maxresdefault.jpg

I made one from 50/50 portland cement and garden vermiculite and, as you can guess, it is very crumbly and basically falling apart after several firings.

Does anyone know which Refractory Castable would be most suitable for this? I am trying to find a balance of a castable which is abrasion resistant & tough, and also will not crack/break when under temperature. I would think the temperature inside would be relatively low (compared to pizza ovens, and kilns obviously). I am also thinking of adding 2-3% steel needles to the castable to prevent cracking.

2nd question: What ratio of refractory vermiculite should I use in the castable? The stove is much more efficient when there is some insulation.

3rd question: Would I benefit from adding a layer of fire bricks at the bottom/half way up the vertical heat riser? Would this increase the efficiency and also add some

Many thanks if anyone can help me with these question marks. I will do a "How to" post here when I get the right materials for anyone interested. Cheers!
 

decorum

Full Member
May 2, 2007
5,064
11
Warwickshire
Slightly tangential I know (sorry) but have you come across breeze-block rocket stoves? Might suit your purpose just as well but removes the need for casting :D
 
Jul 30, 2012
3,571
224
westmidlands
I would not reccomend steel and concrete. Reinforced concrete works by the concrete being stiff to compression and the metal tensile strength, two things coming together to make something better than each of its constituent components seperatley. It does crack if the steel gets wet or oxidises, and I don't think it does too well in fire due to steel expanding and concrete being stiff! As for the mixture engineers think that concrete in the coluseum is still wet (not unset, just wet) so anything you can do to initially dry it, or like the concrete blocks, a mass of little bobbles. Not too much concrete.

Have you ever thought of metal?
 

Mike313

Nomad
Apr 6, 2014
269
22
South East
I built a rocket stove using the cavity blocks as shown in the Youtube link (above) but the blocks cracked and after 3 firings it was no good. I think the reason was the blocks were just lying about outdoors and were probably damp. Maybe if I'd let the blocks dry out really well and built the fire up gradually I might have reduced the chances of the blocks cracking.
 

Unistat76

Member
Dec 1, 2014
26
0
United States
I've built one out of basic red bricks.

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KIMBOKO

Nomad
Nov 26, 2003
379
1
Suffolk
Calcium aluminate cement, Aluminous cement, high-alumina cement and Ciment fondu all names for the same things are castable and refractory should be good for 1250C.
 

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