|
|
Post by garethd on Nov 22, 2020 9:44:46 GMT -8
Has anyone here tried coating the inside of the burn tube with a thin starlite type intumescent mix made from household materials? I watched a YouTube video by NightHawkInLight (1.67M subscribers as of just now) today that gave ingredients and instructions for making which seemed trivial using very simple household ingredients. Given the aim is to have the burn tube as hot as possible, this would seem a pretty neat not to mention cheap way to achieve this, even if it had to be recoated every so often. Possibly one could get away with standard house bricks if one insulated them like this,but presumably cob would last a lot longer too if protected. Any thoughts? Maybe someone with an existing rocket stove would be interested in adding a thin coating to see? link to the youtube video (absolutely no affliation or link to me!) |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 23, 2020 3:51:24 GMT -8
|
|
|
|
Post by wileythenord on Dec 10, 2020 8:27:23 GMT -8
That is insteresting. I may do some trials with that. I could easily make some thin plates to line something cheap like cement board and easily make a burn chamber.
|
|
|
|
Post by wileythenord on Dec 10, 2020 8:58:25 GMT -8
|
|
|
|
Post by closertothehearth on Feb 13, 2021 14:18:03 GMT -8
It's funny you bring thus up. I actually made a very small, 2", batch box a while back from cardboard and NightHawkInLight's DIY starlite. The riser was made from tin cans and was insulated with starlite. Not an ideal rocket by any means. It didn't run very well I think because the starlite was still moist. It did char and protect the cardboard from the flames at first, but eventually the starlite gave way and the whole thing burned up. It was a fun experiment, but I don't think the material would be good for long term insulation. The carbon foam is very soft, so you'd probably have to repack your stove regularly. I'll see if I can dig up any photos.
|
|
|
|
Post by closertothehearth on Feb 13, 2021 17:06:06 GMT -8
|
|
|
|
Post by mudkevin on Oct 1, 2024 10:13:41 GMT -8
I have been experimenting on using cob and perlite for a rocket stove, and I remembered Nighthawk in light's foray into Starlite. He has a newer video where he used Borax instead of baking soda and got better results. This was encouraging to me, since I had tried the baking soda mix years ago and it smelled awful as it burned and was weak. I experimented with different combinations of clay, sand, perlite, flour, corn starch, powdered sugar, and borax. I settled on his original recipe with additional clay, sand, and perlite. For my test batches I used: 60g fine sand, 20g clay, 20g flour, 10g powdered sugar, 10g Borax, and "a bunch" of perlite (basically as much as it would hold together nicely). I'm very pleased with the results! It seems to create quite a strong coating, and even if all organic components were to burn away completely, I would be left with a layer of perlite held in place with clay and sand. My next step is to make a batch-box rocket stove with this "fire cookie dough" coating at least the riser, but probably also the sides and top of the burn chamber (maybe leave the bottom alone since that will have the most friction. The walls themselves will be made of a coarse sand and clay cob that has about 30% by volume perlite mixed in (because it is already in my mix from some earlier experiments).  I can't seem to insert an image, so I placed several in this folder. |
|
|
|
Post by martyn on Oct 1, 2024 10:23:46 GMT -8
Sound interesting please keep us informed…
|
|
|
|
Post by mudkevin on Oct 23, 2024 21:56:53 GMT -8
I got my rocket stove put together, and so far I'm very pleased! I apologize, but the photos are in a new album, located here. There are some pictures/videos of tests I was doing with different versions of the "Starlite" material. There are some random pictures of natural plaster I applied to the walls of our shed, and there are the rocket stove pictures and videos. This is only my second rocket stove. I wanted to test a pretty simplified design: I made 4 rectangles (about 14"x18") using one form for top, bottom, and sides of the firebox, and then 8 rectangles (about 9"x18") using another form for all four walls in two 18" layers for the riser (blocking out a space in one of them for the port). All blocks were about 2.5" thick. I had learned through failure that they can break easily when handling, so this time I put strips of that mesh drywall tape in the middle of each block to give some tensile strength. I also made a 6x6" square piece to act as the bottom of the riser, and against which the four pieces touched. All pieces were made with sand, clay, and perlite, with perlite being about 1/4 of the mix by volume. I coated each rectangle with about 1/2" of my "Starlite" mix, which I called fire cookie dough. I joined all pieces with a clay/sand mortar. You can see that I made triangular pieces in the feedbox and the first half of the riser. That is a mix of clay, sand, perlite, and Plaster of Paris. I mixed it up and applied it directly to the assembled stove (rather than casting separate pieces and inserting them). I made a small fire soon after assembly, then waited a couple days and did a proper fire. I will do a longer test this weekend. I ran a fire in it for about an hour total, with a raging fire only for several minutes. I ran a medium fire to cook a meal on my big wok (the stir fry turned out great!). It seems to be working very well, but I don't know how to assess performance relative to a standard. I can say that after 10 minutes I cannot feel any heat transfer through the walls, but it does eventually come through. I have the whole thing on a hastily-built wooden cart. I realize that's a fundamentally bad idea, but I needed to be able to move it around a bit on my patio, and that is what I could do. I left a board on top of the burn chamber during my testing, with the assumption that the top would get a lot hotter than the bottom, and after about an hour of having a fire, the board was slightly browned. What questions does anyone have? Are there specific tests you would like me to conduct? Any feedback or criticisms? The only things I am currently considering are 1) encasing the whole thing in cob and plaster, and 2) making some rectangles I can slide in from each side, closing off the front like a curtain, to vary the airflow. |
|
|
|
Post by foxtatic on Oct 24, 2024 5:54:00 GMT -8
mudkevin Great work! Appreciate the testing and documenting. I've been looking at refractory coatings and find them to be surprisingly expensive and costly to ship. How well did this stick to vertical surfaces? Did it want to slump off? I'm curious if it stuck so well because your sand/clay/perlite castings were presumably rough to the touch and I wonder how well it would stick to something smoother like clay brick.
|
|
|
|
Post by mudkevin on Oct 24, 2024 20:30:57 GMT -8
Thanks, foxtatic! I'm excited to discover these boards and can't believe the amount of research that has gone on!
This coating may not be refractory--I need to do a much longer burn to see how it holds up. I gave it inorganic components (clay, sand, and perlite) hoping that if the organic matter disappears after hours of high heat I would still have a layer that would hopefully be insulative. As to how well it stuck--quite well, I would say. However, I applied it horizontally--I pounded my wall material with a tamper to compact it into the form, then added the coating and tamped it down gently. Some of my pieces were made like this, with the coating being put onto a fresh block, while others were completely dry when I smushed the coating down with my hand. The coating is quite sticky, probably thanks partly to the powdered sugar, partly to the flour, and partly to the clay. I am guessing it would stick well to a smooth vertical surface, though perhaps it would peel away after some hours in the fire (there is a bit of separation apparent at the front of the feedbox. I am not sure, but I think it is a piece where the topping was added later.)
One thing that was interesting: if I applied a torch to the coating, it blackened right away. I assumed that within the firebox it would also blacken right away. However, with the air being pulled in along the sides, it took a long time before it was hot enough in the firebox for the walls to blacken. If I understand what is happening when it swells and blackens (the intumescence): the sugar melts and the Borax adds CO2, resulting in a carbon foam that then radiates heat away quickly. I did a lot of tests of different combinations of material and found the flour and corn starch were not necessary to get the intumescent effect, only the powdered sugar and Borax are needed. The flour made it more dough-like, the corn starch made it smoother.
My combination of perlite, clay, and plaster of Paris seems to be good so far (it is seen in the triangular pieces of the firebox and riser). I think that might be a good coating for withstanding the heat of a rocket stove, but that too needs more time to assess how it holds up. Thanks to the plaster, I think it would stick well to a smooth surface, but also because of the plaster it has a very limited working time compared to the "cookie dough" coating (I made a big batch of that dough, covered it, and used it over several days--it was fine as long as I prevented it from drying). For my plaster mix I made a clay slurry using 1 part clay, 1 part water, then added about 10 parts perlite, then added more water, if needed, to have it all a little bit runny, then added 3 parts plaster, mixed, and applied quickly (it started hardening in just a few minutes).
|
|
|
|
Post by mudkevin on Oct 26, 2024 12:04:35 GMT -8
I ran the stove hot for 3 hours today, and my conclusion is that the "starlite" or "fire cookie dough" coating will NOT be suitable for long-term use. The intumescent properties of the coating would be good for stopping the spread of fire, like if you had it on your walls. However, after long, high-heat exposure in a rocket stove, all the carbon disappears, and I was just left with a fairly brittle layer of perlite, sand, and clay. In the hottest spots, such as where the fire hits the back wall of the riser, the coating seems to be falling away. This layer may provide some insulation, but it may be better to put it on the OUTSIDE of the brick. I accidentally installed one of the riser bricks with the coating facing outwardly, and it was about 80 degrees cooler than the brick on the other side that had the coating facing the inside of the riser. However, I have no bell over my riser, and if I did the coating on the outside of the riser would probably look like the one on the inside.
The other materials I am testing are doing very well. My compressed "bricks" of sand, perlite, and clay seem to be holding up perfectly, and so is the material I used for the triangular corner areas of the firebox and riser (sand, clay, perlite, and Plaster of Paris). I will do further assessment and take pictures when it is all cooled off. My bricks were mortared together with a sand/clay mix, and this has cracked quite a bit in places.
|
|
