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Post by alamojo on Mar 22, 2011 5:30:13 GMT -8
Hey gang, I'm interested in making a rocket stove inexpensively. The youtube video which describes making one out of 16 bricks uses unfired adobe bricks. I'd like to try making these -- has anyone made these? Any advice/tips?
Alan
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Post by Donkey on Mar 22, 2011 8:25:21 GMT -8
Yes I have.
I use adobes to put together benches and stove bodies quickly. It's a REALLY quick way to work and bricks are easy to make. I'll pop out a few on my days off or in my free time and slowly accumulate a stack to use in various projects..
Yer asking specifically about using adobes in the heat riser and such. Regular old adobes work fine, though I personally like a mix with lots of wood ash in it. I use the ash to replace most (if not all) of the sand. This will lighten the bricks for a more insulative quality and they become FAR more fire resistant. Any sand you use should NOT be quartz. Quartz and some other crystalline sands will expand differentially under heat and crack apart your brick. Use instead black sands, silica sand (wear a mask while dry working) and/or grog.
I use a little straw in the mix, I know it will burn out but I do it out of force of habit more than anything. I do think it's good to use, though I can't put my finger on why. If you do use straw, keep it fairly short. It's difficult to get long straw to lay down nicely and form a good brick.
Whatever size you make your brick form, you will save yourself a lot of trouble if it's dimensions are doubled on each next larger face.. Twice as long as it is wide, twice as wide as deep. This way, layout and stacking is easy to figure out, easy to pull off. Clean WELL and wet the form(s) before filling with mix each time, otherwise it will be hard to get the bricks out cleanly.
Prepare a place where they will stay till they're dry. I use sheets of plywood so I can drag 'em around the yard or just do 'em right on the ground.. If you use plywood or anything other than dirt, sand the surface a bit so they won't stick to it.
You want a mix that is wet enough to fill the form easily and get into all the corners but dry enough to hold it's shape when you pop it out of it's form. Wetter mixes will come out easier, but will slump if too wet. Lay the wet form down, plop in the mix, massage it into the corners, lift the thing up and gently (but firmly) knock it on the ground (surface) to pop the brick out, repeat. When they are (just) dry enough to move without screwing up, flip 'em on their edges to finish drying.
When you lay the bricks, use as little mortar as possible. Mortar is for holding the brick apart so it doesn't wiggle about, NOT for holding them together. Just dip the adjoining faces in clay slip and stick down. Check each brick, if it wiggles pull it up and use JUST enough mortar to fill the low spot then re-apply the brick. Adobes can be ground or broken to any shape or size. I'll rub a brick on a rock, another adobe, a chunk of concrete or whatnot to flatten, for other shapes wet slightly and carve with a machete..
For the high heat areas I would use a mortar of wood ash and clay slip. You will want to put it all through a fly screen, it's gotta be fairly fine if you follow my directions and make thin joints. I usually put the dry ash in a mixing bucket first and add slip, mixing till the consistency is right. Not too firm, it's gotta squish a bit, not too wet, it's gotta hold up the brick.
Umm.. There are a million fine points though they're pretty self evident once you get going. Practice building one OUTSIDE first.. You'll NEED to do that anyway to be totally sure that your local clay soils can withstand the heat. Build one outside and fire it to within an inch of it's life!! Anyhow, it will also give you the experience you need to confidently build on in your house. There will be issues, there always are and it's best to work them out in a safe way. When you get yer mock-up right, re-build inside and enjoy!
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Post by josephjcole on Mar 23, 2011 4:07:25 GMT -8
Donkey,
very thorough answer... thanks...
one question though, you mention avoiding quartz sand, while saying silica sand is ok to use. I have to admit if someone randomly asked me yesterday what the difference was between quartz sand and silica sand I would have said there wasn't a difference.
Have you had trouble with quartz sand in the past? What is the difference between quartz sand and silica sand? Maybe particle size?
just curious, thanks
Joe
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Post by Donkey on Mar 23, 2011 8:41:31 GMT -8
I'm not exactly sure..
Silica, apparently (I haven't used it myself as its an expensive bagged product) can take high heats without expanding much..
I HAVE used quartz sand with poor outcomes. The stuff will expand differentially under heat, warping on one axis more than another. It tends to crumble the mix over time. One of the funny properties of crystalline structures.
I suppose it's a bit like piezo chrystals.. If you apply energy, they warp, if you warp them, they emit energy. Modern sonar equipment uses the piezoelectric effect to emit high frequency sound. If yer the kind of geek that loves this kind of thing, you should check it out.. Pretty wild stuff.
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Post by alamojo on Mar 23, 2011 13:02:14 GMT -8
Donkey, thanks for the detailed answer.
The other possibility I'm looking at is, in a Rocket Stove presentation I found on the web (don't have the URL at the moment but I could find it again), there was mention of creating bricks using vermiculite and cement (see recipe below). I wonder if anyone's tried this?
1 liter vermiculite
170g cement mix
290g water
don't tamp, dry 10 days
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hpmer
Full Member
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Post by hpmer on Mar 23, 2011 15:46:57 GMT -8
There have been lots of cautions against using portland cement in the mix as it won't stand up to the heat.
I've used furnace cement mixed with perlite for the burn tunnel/fire box with (so far) good results and clay mixed with ash for the heat riser, but don't know how it all will stand up longer term, though I assume it should be fine.
Not the easiest thing to mix as the cement had the consistency of modelling clay, but in the end it worked pretty well. I got the cement in small buckets at Home Depot and the perlite from the local Wal-mart garden center.
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Post by Donkey on Mar 23, 2011 16:13:49 GMT -8
Right.
If you need, for some reason, to use a bought product (like unsuitable natural clay soils), go for refractory cement. Don't use recipes with portland cement in them. At the VERY least, be highly skeptical of them.
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Post by alamojo on Mar 24, 2011 4:31:43 GMT -8
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Post by josephjcole on Mar 24, 2011 5:32:25 GMT -8
I'm not exactly sure.. Silica, apparently (I haven't used it myself as its an expensive bagged product) can take high heats without expanding much.. I HAVE used quartz sand with poor outcomes. The stuff will expand differentially under heat, warping on one axis more than another. It tends to crumble the mix over time. One of the funny properties of crystalline structures. I suppose it's a bit like piezo chrystals.. If you apply energy, they warp, if you warp them, they emit energy. Modern sonar equipment uses the piezoelectric effect to emit high frequency sound. If yer the kind of geek that loves this kind of thing, you should check it out.. Pretty wild stuff. Interesting stuff... I'll have to look into it more. Quartz is silica, so I have to believe they both expand at the same rate. It's been a while since I read the exact numbers but I think it's something around 2-3% expansion at 1060 degrees ferihneight. It must be as you say though that the crystalline structures are different... I've made bricks using silica sand (which is only an expensive bagged product when it not available locally  ) with out issues firing up quite hot. Anyways I'll go geek it up elsewhere... thanks for the info. Back on topic... alamojo, there is very likely suitable soil around. However if you are unable to find any, the next best thing is to buy fire clay from your local pottery supplier. It's not free, but it's a lot cheaper than high temperature cement. Use the fire clay the same way you would your local clay, mixing in whatever else you feel necessary. Joe |
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Post by Donkey on Mar 24, 2011 8:01:08 GMT -8
Try your local clay soils first. Make a brick or a ball (puck) of clay mixed with sand so it doesn't crack when drying. How much sand?? Dunno, depends on your soils. Try different combinations, the ones that crack when drying need more sand, the ones that crumble less. When you've got yer mix down and it's dry, stick it in a fire where it can get good and hot.
Inspect your outcome,it should stay in one piece and fire hard ( or bisque hard that is). It's likely that the piece will be a little crumbly around the edges, that's ok. It should be MOSTLY solid though and hold together well.
I'm sure I forgot to add something.. Anyone wanna chime in here?
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hpmer
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Post by hpmer on Mar 24, 2011 14:14:46 GMT -8
Donkey,
I liked your idea of using ash in place of sand in the mix and have used it with success. Any reason you are reverting back to sand in this recent post?
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Post by Donkey on Mar 24, 2011 16:53:19 GMT -8
Donkey, I liked your idea of using ash in place of sand in the mix and have used it with success. Any reason you are reverting back to sand in this recent post? Umm.. Good question. I guess I've got my mind on standard adobe, which I use quite a lot of. I've found wood ash to be great in high temp areas like the heat riser. I've used it alone with clay slip to make a home made refractory to line my WVO foundry. It seems that alone though it's lacking in something.. Body, for want of another word. My wood ash mixes tend to crack when drying and I've found that it can be difficult to get enough ash into the mix and still get a workable batch. I've been thinking that a little grog would be helpful, or maybe a touch of the right kinds of sand. I've used rice hulls and it works, it's light too for better insulation. So.. I still advocate the ash mix.. Just forgot to pound on it, got distracted with the adobe thing.. I didn't mention pearlite/clay mixes either. I also forgot to mention that there's no particular reason to make only bricks with the mixes.. The various mixes can be poured or tamped into forms and the whole inner works could be cast in one or a few simple stackable pieces.. I've tried cardboard, which is great 'cause it can be burned out after. Waxed cardboard is better as it won't get soggy and droop. I haven't worked out ALL the bugs, like the best shape, or the best way to hold it all together, or how to encourage the bits to dry through the waxed cardboard in a timely manner, or the fact that second hand waxed boxes tend to be full of air holes (to keep the veggies fresh) that need to be patched or covered in some way to hold in the mix.. It does promise to be a good system though. |
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Post by blindpig on Mar 27, 2013 8:49:56 GMT -8
Hi Y'all
Just throwing in my two cents(about what it's worth). I understand folks not wanting to use Portland cement because of it's failing at high temps but I've been adding small quantities
to my refractory mix,which allows removal of the molds quicker than not adding it. The mix I've used for my foundry furnace is:
1-part fire clay
2-parts brick grog
1/2-part Perlite
!/2-part Portland cement
The lining has lasted 5 or 6 years with moderate crack filling and It's melted cast iron.
The Portland and Perlite burn out at high temps leaving insulating voids.
As I said $.02 worth.....
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Deleted
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Post by Deleted on Mar 27, 2013 9:08:15 GMT -8
...which allows removal of the molds quicker.... Impatient as I am I like to use a bit cement, but a smaller amount. Will dry faster too.  |
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) with out issues firing up quite hot. Anyways I'll go geek it up elsewhere... thanks for the info.