Testing of mini rocket stove made with air crete an ceramic fiber.

I had an idea after talking with a friend of mine, people make vases out of cloth and concrete, I decided to make a holder for my chimney on top of the air crete rocket stove, it is working like a champ. This is ugly as sin, but it burns like a forge now.

It looks HOT in there.

So what exactly is aircrete?

I believe it's aerated concrete. The commercial brands we have here are Ytong and Hebel.  It's insulating but ordinarily will crack under heat.

Yes I should of said...how is this aircrete heat resistant, is it due to the ceramic fibre mix?
I have seen that chap honeydew (or something like that) but  I did not get how he was making it heat resistant?
It just seems a little bit null and void compared to the 5min riser concept?

Honey Do Carpenter uses waterglass in his forge.
He probably does the same with his rocket stove.
It is way cheaper than duct for supporting a ceramic fiber  riser,  and if you are building in it anyway, why not use it?
If you can get aerated concrete to take the heat,  it can replace expensive refractory cement or firebrick.

I saw him painstakingly apply water glass to the surface of some air crete.  Is that what he is doing to the whole hot facing surfaces of his rocket stove?

However, casting the core in air crete and then lining it with ceramic fibre blanket sounds very doable.

Fox James wrote:Yes I should of said...how is this aircrete heat resistant, is it due to the ceramic fibre mix?
I have seen that chap honeydew (or something like that) but  I did not get how he was making it heat resistant?
It just seems a little bit null and void compared to the 5min riser concept?

Normal air crete will not work, it will break down under high temp.    However  I am testin the Honey Do Mix   I bought the recipe off their Etsy page,    I am also trying other ideas I have of my own.   So I am testing all of these as I want to find the highest quality product for the lowest price.      I do want to move away from ceramic fiber because breathing the fibers is a bad thing, and re making a perlite / sodium silicate riser every few years may not be such a bad thing.

I like to test multiple options, and go with the one the fits my needs.

What I have learned with my test setup,

A thin layer of aircrete does not hold up very well, I had 1/8th of an inch and it did not work.

Using cloth and concrete in the riser just does not hold up.

I have found extending the burn chamber with a chimney pipe increases the burn as the pipe heats up and warms the air entering the pipe.


I have learned much from my test setup,  will build another and see if I get closer to my goal of having a rocket stove that burns long enough to cook without me having to watch it.

Is 40 minutes cooking time long enough?  That's about what you get with a batch box.

Graham Chiu wrote:Is 40 minutes cooking time long enough?  That's about what you get with a batch box.

I think so if....    

You combine the batch box with a cob oven.      If one were to dump that heat into the right sized cob oven, one with the mass and the proper insulation you could extend the cooking time because the heat would be banked in the thermal mass.


I am still working out the mechanics of how this  could be done, but it is a goal of mine in this build.

Cheers.

Graham Chiu wrote:Is 40 minutes cooking time long enough?  That's about what you get with a batch box.

One of the ideas I have of doing this is heating  a chunk of steel till it is glowing hot in the rocket oven, then putting that into a heat rention cooker and cooking.    I have seen this done with Solar, and I think the rocket stove would do the same.

Example ->

https://www.builditsolar.com/Projects/Cooking/StoredHeat/StoredHeat.htm

With a rocket stove, you already have residual heat in the brick work, and coals.

Graham Chiu wrote:With a rocket stove, you already have residual heat in the brick work, and coals.

This is true.      However the only location that one can cook with it is at the barrel.         I was thinking what if that barrel was put in the middle of a cob oven?       would it not heat up the thermal mass of the oven to a high temp, and keep the smoke out of it like a standard cob oven?

I am not sure of this, but something I would like to test.

Mart

You mentioned barrel. Are you building a cooker and heater, or just a cooker because if the former you don't need a barrel.

You can dump heat from the riser into a brick or cob oven, and depending on how well insulated it is you can cook for hours or a day. My brick oven drops from 300 deg C to 100 deg over three hours with no insulation.

You can cook over the combustion chamber if the steel is thick enough.

Fox James wrote:So what exactly is aircrete?

Hi Fox,

Aircrete is a slurry of portland cement and water to which a load of soap foam has been mixed in.  This mixture is then placed in a form and allowed to dry.  As with concrete it is best if the humidity is maintained for several days even up to 2 to 3 weeks, for improved strength.  If you want it to be very insulating you use more foam.  More strength, use less foam and augment the slurry with some sand and/or perlite.

I understand why Mart did not want to elaborate on the refractory mix as he has purchased it from Darwin (the honey do carpenter).  I have thought about it, but have not yet paid the $8 that he is selling his recipe for.  I will probably do so, but as of yet what I am sharing is what I gleaned from one of his videos.  His initial refractory mix used diluted sodium silicate (water glass) like 15% +/-, some clay?, perlite, and portland.  Then he also coated the exposed surfaces with water glass, allowed it to soak in and then fired it.  In the video (which I watched a while back) he mentioned using bentonite clay and trying to get it to absorb the water glass and then using it in his refractory mix.  He has not to my knowledge publicly shared the results on you tube.  I do not blame him as he is trying to sell the recipe not give it all away.

My total knowledge of aircrete at this instant in time is from you tube, but I am currently putting together a foam machine so I can begin to do some experimentation firsthand.  I am planning on using aircrete for lower temperature areas of the rocket engine for my rocket oven.  I am using refractory materials, brick, duraboard, and the ceramic blanket with the aircrete holding it all together and providing a very light weight insulating outer shell.  When I get it put together, I will be sharing it here in the rocket oven forum.

Sincerely,

Ralph

Mart Hale wrote:What I have learned with my test setup,

A thin layer of aircrete does not hold up very well, I had 1/8th of an inch and it did not work.

Using cloth and concrete in the riser just does not hold up.

I have found extending the burn chamber with a chimney pipe increases the burn as the pipe heats up and warms the air entering the pipe.


I have learned much from my test setup,  will build another and see if I get closer to my goal of having a rocket stove that burns long enough to cook without me having to watch it.

Hi Mart,

Aircrete would not work well at all in a thin layer.  It has very limited structural strength and like its older brother concrete is much stronger in compression than in tension.    I don't believe that sufficient test work has been done on aircrete, but with concrete the strength when in compression is 10 times what it is when in tension.  

As I stated in another post, there is a trade-off with aircrete between strength and insulation value.   If you make it more like concrete and less like aircrete you improve the strength at the cost of increased weight and reduced R value.  

Another issue with using aircrete in a rocket stove is that with rocket stoves folks like to burn them really to cure the cob, etc.  With aircrete, you would want to wait 2-3 eeeks before firing.  As soon as you fire, you basically cause the aircrew to set and its strength will stop increasing.  This is all supposition and is based on my engineering knowledge of materials, but when I went to school, there was no such term as aircrete.  Thus what I have started in this paragraph is based on my existing knowledge of materials applied to a brand new material with very limited test data.  That concludes the fine print.

Now for a completely hypothetical question.  How many of you (me included) rocket stove/oven/mass heater/cooker enthusiasts/experimenters/hobbyists/experts would like to spend days and weeks on their latest project and then have to wait 2-3 weeks before firing it up so that the aircrete can properly cure.   SURE WE WILL!!!  ;-)

Sincerely,

Ralph

HA HA Ralph...   2-3 weeks …. 2-3 minutes is more like it!   You got this ...

Precisely Thomas, precisely!!!

Ralph Kettell wrote:Precisely Thomas, precisely!!!

Everything you said was on target for aircrete Ralph.     I have been making rocket stoves out of ceramic fiber and chicken wire alone.     I can see an orange glow thru 3/4 of an inch of the insulation, outside temps hit 400 degree per my laser.      But the ability to quickly test different designs with this method is awesome :-)

I have built a rocket oven and I tell you I am getting fat quick ;-)      I may not be able to move to build more stoves LOL

I have been using the J tube like a Tlud  stove,   I fill up the j with wood and light it from the top, which works well with my oven for long burn times.    

But since I have been adding more insulation to the rocket oven, I am starting to see that I don't need to be going for long burn times, but just heat that baby up and let the oven do it's job, if you are at 450 F   or 500, you don't need to cook for long.

I am still needing one more ingrediant for the Honey Do refractory mix, sigh,  I will just play with my other toys till I get that :-)

One other thing I have learned with air crete is corners are it's weak spot the more round the edges the better off it will be to not be broken.

Mart Hale wrote:


I am still needing one more ingrediant for the Honey Do refractory mix, sigh,  I will just play with my other toys till I get that :-)

What ingredient are you missing? I may be able to help you source it as I have been gathering these things also.

Sincerely,

Ralph

Ha Ha Ralph;   Hinting for a recipe?  :)    I hope it works for you Mart.

Mart Hale wrote:One other thing I have learned with air crete is corners are it's weak spot the more round the edges the better off it will be to not be broken.

This is a function of my earlier comment about concrete and aircrete re.  compression vs. tension.  When you push on a corner of aircrete, you are putting it in tension and it breaks right off.  

Conversely, when you stand on or stack blocks you are putting them in compression.  When you put a block on sand and stand on it like Darwin did in one of his videos, he concentrated his weight in the center of the block, and it cracked in half.  Again this area was put in tension.

When you stack aircrete blocks for a wall they should be fairly strong, but be careful that your design protects against excess perpendicular loads which will result in ... more tension.

Sincerely, Ralph

Ralph Kettell wrote:

Mart Hale wrote:


I am still needing one more ingrediant for the Honey Do refractory mix, sigh,  I will just play with my other toys till I get that :-)

What ingredient are you missing? I may be able to help you source it as I have been gathering these things also.

Sincerely,

Ralph

Actually I am getting clarification from them about one of the ingredients,  It is like I just built a variation of the rocket oven, but I don't want to post a video showing my design as I want Paul to sell videos and plans for his gig.       :-)

It is hard to think in terms of open source once you have bought plans from someone.      I think the Honey Do needs a forum.

thomas rubino wrote:Ha Ha Ralph;   Hinting for a recipe?  :)    I hope it works for you Mart.

Believe it or not, Thomas, that was not on my mind.  

As I said, I am going to pay him the $8 at some point.  I don't mind paying someone for their effort.  I just have no need for it until I finish building my foam generator.  Note that I did not call it a foam mate.

;-) ;-) ;-)

Sincerely,

Ralph

I've used a calcium aluminate cement,not sold as a refractory, but made with the same materials, as the cement portion of perlite concrete.
It's commonly available at the Home Depot for around $20.00 for 50lbs.



I want to try it in other forms:
-Ferrocement with basalt reenforcement instead of steel.
-Hot face for rockwool or ceramic insulation.
-Aeroconcrete firebox ,riser maybe even bell.

William Bronson wrote:I've used a calcium aluminate cement,not sold as a refractory, but made with the same materials, as the cement portion of perlite concrete.
It's commonly available at the Home Depot for around $20.00 for 50lbs.

Hi William,

Can you please tell me/is the brand name of this material that Home Depot sells.

I am thinking it is Rapid Set Cement All.  I told Thomas about it on another thread post, but I told him, that while I bought some, I have yet to try it out and test it.  That is still the case.

Thanks.

Sincerely,

Ralph

William Bronson wrote:I've used a calcium aluminate cement,not sold as a refractory, but made with the same materials, as the cement portion of perlite concrete.
It's commonly available at the Home Depot for around $20.00 for 50lbs.



I want to try it in other forms:
-Ferrocement with basalt reenforcement instead of steel.
-Hot face for rockwool or ceramic insulation.
-Aeroconcrete firebox ,riser maybe even bell.

Is this what you are refering too?

What have been your results?

Thanks!

https://images.homedepot-static.com/catalog/pdfImages/30/3063f813-032e-4c2a-b107-aa384065812f.pdf

Mart Hale wrote:

Graham Chiu wrote:With a rocket stove, you already have residual heat in the brick work, and coals.

This is true.      However the only location that one can cook with it is at the barrel.         I was thinking what if that barrel was put in the middle of a cob oven?       would it not heat up the thermal mass of the oven to a high temp, and keep the smoke out of it like a standard cob oven?

I am not sure of this, but something I would like to test.

Mart

Actually you have additional options, for example Matt Walker built a RMH in a corner ( https://youtu.be/v20dCSxV5ow ) and has tried a heating plate as well as a door that gives access to a space just in front of the wood feed, away from the burn tunnel from what I could see. He's baked bread in it in one video, and I think mentioned cooking soup as well. Not a huge cooking area of course, and introducing points where heat is removed will lower the burn temps and efficiency of the burn.

While the barrel top is a convenient spot, those who are using brick or earthen bells instead seem like good candidates for including a recess or two near the top where you could remove a brick to expose a thinner surface that heats up quicker and gets hot enough for cooking.

That's the stuff!

I have built more than I have burned,  but its heldup to those few burns great.
I have three projects that are CementAll/Perlite,two of them yet to fired.
I did crack that j-tube riser I but it had been outside in the cold and rain, I got impatient 😕
I need a dry place to work with fire projects, but I have other pressing needs, and lots of distractions...
Dgd
I'm confident in it enough to recommend others try it out.
It's cheap and easily availed and has a crazy short setting time.

Mark Tudor wrote:

Mart Hale wrote:

Graham Chiu wrote:With a rocket stove, you already have residual heat in the brick work, and coals.

This is true.      However the only location that one can cook with it is at the barrel.         I was thinking what if that barrel was put in the middle of a cob oven?       would it not heat up the thermal mass of the oven to a high temp, and keep the smoke out of it like a standard cob oven?

I am not sure of this, but something I would like to test.

Mart

Actually you have additional options, for example Matt Walker built a RMH in a corner ( https://youtu.be/v20dCSxV5ow ) and has tried a heating plate as well as a door that gives access to a space just in front of the wood feed, away from the burn tunnel from what I could see. He's baked bread in it in one video, and I think mentioned cooking soup as well. Not a huge cooking area of course, and introducing points where heat is removed will lower the burn temps and efficiency of the burn.

While the barrel top is a convenient spot, those who are using brick or earthen bells instead seem like good candidates for including a recess or two near the top where you could remove a brick to expose a thinner surface that heats up quicker and gets hot enough for cooking.

Thanks for pointing that out Mark,

I love the direction that Matt Walker has been going.    


As I think of it I did once dig in the sand a trench and put a pan on top of that with a riser at the end, it did cook.