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Post by pinhead on Jan 17, 2014 11:51:59 GMT -8
I seem to have stumbled upon a source of very fine sand for use in my stove experiments. It seems to be relatively pure, though it obviously has some contaminants. The sand was sourced from the base of a sandstone cliff face. There is some rock which I sifted out using a steel screen from a window. www.youtube.com/watch?v=eRIbYmhqekw&feature=youtu.beLately I've been experimenting with different mixtures of sand/clay/ash and have noticed some weird characteristics of this sand when compared to "normal" road sand which is much coarser. First, it very easily "packs" when wet. If I dump some of this sand into a bucket that is half-full of water -- then pour out the water that wasn't "absorbed" -- the remaining sand holds together to the point that I can turn the bucket upside-down and the sand won't fall out. The top inch or so of the sand acts much like a very soft gel which will sag when the bucket is tipped on its side. It doesn't seem to want to "detach" from the rest of the mass of sand, however. This "gel" will separate if shaken hard enough, leaving the rest of the sand stuck in the bucket, which is very difficult to "scrape" out due to it's compactness. When impacted, the surface of the sand is very hard but can be easily penetrated - much like a Non-Newtonian fluid. When heated and thoroughly dry it will turn a dark red color (the same color as the original sandstone) -- in the first picture you can see the darker red area compared to the lighter outside edge. I covered the top of the barrel with this "pure" sand and let the stove burn over night - temps at the top of the barrel were touching on 800°F for about 30 minutes last night before I went inside for bed. The stove continued burning and I will see what the results are this evening after work. From what I have seen, I expect it to be very hard with a "sandy" surface which will easily rub off. When poured "into" water the water turns brownish-yellow and there will be a "froth" on the surface -- the second picture. Does anyone have any idea what the brown-yellow "froth" that has been left behind in the water is? Is it simply super-fine clay? It doesn't seem to be settling out of the water at all (if it is, it's VERY slow). This would explain why the "pure" sand seems to have hardened on the top of the barrel (I'll take a more thorough look tonight). Attachments:
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Post by matthewwalker on Jan 17, 2014 12:25:40 GMT -8
From what you describe it sounds like you've got a bit of clay in there as well. When it's dry does the powder kinda feel like talc on your hands? The top of the barrel looks like sand, but if it's staying together when dry it's got some clay in it, in my opinion.
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Post by Donkey on Jan 17, 2014 13:22:42 GMT -8
Ditto what Matthew said on the clay.
Really fine sand tends to be roundish as well; broken up by water action, it will have been tumbled round and smooth. If your sand fits that description, it may not be adequate for making cob/plasters, etc.. On the other hand, you say it's drying hard. If it works, then it works..
Red color may be iron content oxidizing. Rust makes for good pigment.
In your picture, it looks kinda like quartz sand.. Does it have little crystals in it? Turn it in the sun, any little shiny bits?
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Post by pinhead on Jan 17, 2014 13:55:11 GMT -8
From what you describe it sounds like you've got a bit of clay in there as well. When it's dry does the powder kinda feel like talc on your hands? The top of the barrel looks like sand, but if it's staying together when dry it's got some clay in it, in my opinion. It always just feels like super-fine sand. I'll try to see if I can get some of the stuff to "stick" to my hand and get rid of the sand so I can feel the other stuff. I'll also see if I can do the "water test" I've seen described somewhere on the forum. As seen in the video, when I was screening the stuff there was an appreciable amount of dust. When I was screening I simply assumed it was "dust" which would be detrimental to the final mixture. Looking at it now, the dust may have been super-fine and dry clay powder blowing away. Ditto what Matthew said on the clay. Really fine sand tends to be roundish as well; broken up by water action, it will have been tumbled round and smooth. If your sand fits that description, it may not be adequate for making cob/plasters, etc.. On the other hand, you say it's drying hard. If it works, then it works.. Red color may be iron content oxidizing. Rust makes for good pigment. In your picture, it looks kinda like quartz sand.. Does it have little crystals in it? Turn it in the sun, any little shiny bits? The sand was definitely broken up by water being, at the base of bare sandstone next to a lake. I'll have to get some pics of the stone... Maybe it will be easier to track down the "ingredients." **EDIT** Post Rock Images - Minooka Park Area This is pretty close to the same area and the same type of rock.  **EDIT** I've already used this sand directly beneath the barrel at a 1:2 ratio of pure(ish) clay to this sand, IIRC (with no fiber/straw). It dried extremely hard and didn't crack at all (can I emphasize extremely any more than that?). I don't think I could break it up with anything less than a punch and a hammer. Unfortunately sand tends to "rub" off the surface and over time leaves a mess on the floor around the cob. Also, if water is poured/dripped on the surface, the sand tends to come loose and the water will leave "trails" of loose sand. I used this mixture to build the "plenum" at the base of the barrel and is built probably 8 inches thick at the base. I don't know how well it holds up to heat because it's so thick that it never gets very hot; I only burn the stove a few hours while I'm in the shop and maybe a full-day on a Saturday which means the mass doesn't get to heat-soak. On the other hand, being at the base of the barrel it should be subject to pretty high temperatures considering the half-barrel bells get up to 200°F. I had the primary heat exchanger (vertical barrel) off the other day and noticed that the cob hasn't deteriorated at all since I built it. I built the "bench" before I discovered this sand so I can't see what happens when it is heat-soaked to 200°F or higher. Then again, I've had the barrel above 850°F for extended periods of time feeding directly into the cob bench so perhaps it's already passed the test. Unfortunately my method of "experimenting" with cob has been by mixing it up until it "feels" right and then building with it. I guess I should try to make some "pucks" the way Donkey recommends to see how this stuff holds up to some real heat and track down some concrete ratios. More to come. |
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Post by matthewwalker on Jan 17, 2014 14:05:35 GMT -8
Some flour paste in your mix will bind all that stuff on the surface and greatly reduce if not eliminate "dusting." You can even paint it on as a top coat, some of the dust will mix with it as you go, just reincorporate it into your paste and you'll end up with a paste rich plaster for a top coat.
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Post by pinhead on Jan 17, 2014 14:20:36 GMT -8
Some flour paste in your mix will bind all that stuff on the surface and greatly reduce if not eliminate "dusting." You can even paint it on as a top coat, some of the dust will mix with it as you go, just reincorporate it into your paste and you'll end up with a paste rich plaster for a top coat. That's very interesting. How do I go about finding the correct ratios? How much is "some" flour paste? |
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Post by matthewwalker on Jan 17, 2014 14:37:43 GMT -8
It's so forgiving, just give it a try. Mix up a couple cups of hot water with a 1/2c or so of flour, add a bit of that to some plaster until it looks good. I dunno, I know I'm not being very helpful, I tend to be super casual about the mixes and just go by feel. It's really intuitive once you start playing with it. Donkey will probably have better advice in regards to ratios and such. Donkey?
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radek
Junior Member
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Post by radek on Jan 17, 2014 15:20:47 GMT -8
when i make my flour paste ,i take 1 gal of water and 1 and half cup of flour. i take one quart of water out of the 1 gal and mix it with the flour making kinda pancakes dough.Bring the 3-4 of gal to boil and the pan cakes dough to boiling water and mix it a lot.It will get thicker and kinda translucent.Thats my flour paste,and how Matthew sad its forgiving and really works in finnal layes of plaster against dusting off.When i use it for top layer i take it thru strainer to get little chunks out.
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Post by Donkey on Jan 17, 2014 23:40:26 GMT -8
Oh.. I've had bad results painting flour paste on.. Especially in hotter areas!
Better to mix it in! You can also use prickly pear juice.
I've actually been using exterior grade white glue as an after-the-fact paint over the top to lock it down kinda thing.
It's not as natchy-natch as I usually like, but it works REALLY well and it's pretty cheap.
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Post by pinhead on Jan 20, 2014 7:06:42 GMT -8
It seems that after the first "firing" during which the sand had hardened, it reverted back to "normal" sand on top of the heat riser. It did keep it's distinctive red color, though. I may try to "wash" the sand to get it as pure as possible so I know the ratios I'll be working with. It may turn out that whatever is currently mixed in the sand isn't clay at all - as it doesn't seem to help bind anything once heated. I'm in the process of making some test pucks in order to test different ratios of sand/clay/perlite which will be hard enough to make a semi-portable (using the term very loosely) PVDB RMH. I'll probably also try to make some hardened adobe bricks using the sand/clay. Unfortunately I don't have any way to "fire" the mixture besides building the thing and burning it -- which can be pretty time-consuming. I may try to build a Rocket stove for the specific purpose of firing bricks. It'll probably end up doing double-duty as a wood-fired grill.  |
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Post by Dan (Upstate NY, USA) on Jan 21, 2014 14:44:39 GMT -8
I think you may have some salts in there?
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Post by pinhead on Jan 22, 2014 7:40:54 GMT -8
I'd rather not taste it to find out... Is there another way to test for salts/impurities?
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Deleted
Deleted Member
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Post by Deleted on Jan 22, 2014 8:56:04 GMT -8
I think you may have some salts in there? Unlikely, as soluble salts would have been washed out long ago. |
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Post by pinhead on Nov 12, 2014 10:19:32 GMT -8
I tore the stove down for a realignment (the layout wasn't working well in the shop) so I got to see just how hard this stuff was.
I literally had to take a long screwdriver and an 8lb sledge hammer to bust it apart.
I can see how adobe buildings can last so long after working with this stuff.
Other than throwing the chunks into a 50 gallon barrel and submerging them in water, what's the easiest way to reuse it? We've had almost 4 days of below 20°F this week so it'd be a PITA to go try to dig up more clay...
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Post by Donkey on Nov 16, 2014 10:29:43 GMT -8
Smack the big chunks up with the sledge, it should crush MUCH easier when dry. Quite often, cob and/or clay chunks will be quite difficult to re-hydrate, the surface will form a "clay pan" sealing out water so that it will only go so deep.
Bust it, soak it, rework and go. That rework bit is important, you want to reactivate the clay to be workable by walking on it.. Kneed that dough then reuse.
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