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Thread: DIY Refractory Compositions

  1. #11
    Do not use this recipe!!!!

    50 pounds of play sand
    10 pounds of portland cement
    10 pounds of Bentonite
    8 quarts of Perlite
    little water as possible

    Lasted ten pours and was falling apart so badly pieces was getting in the melt.

    Do not use this recipe either!!!

    60-75 pounds of 3000 degree commercial refractory
    8 quarts perlite
    1 bag of Flor-Dri
    little water as possible

    One of the components melts out and doesn't even leave a trace.
    Shortly begins to crumble from the top down.
    It is evidently not wise to alter commercial refractory recipes ops:

    Sorry I don't have a recipe that works well but some of the others on this post look pretty good!


  2. #12

    not as bad as it could

    long post ahead, but I'll keep it as close to topic as I can....

    this is what I used in my mini furnace and I had no problems doing temps that completely vaporized the MAPP gas brass burner nozzle (it was meant as a test run to see how a larger one would hold up) without major structral also melted al easily and is sturdy sturdy stuff...

    furnace was a pair of coffee cans end to end and filled with the mixture...a 3" dia bore, with roughly an inch of the refractory.....the outside of the cans got hot enough that welding gloves were needed.... goes...for the small batch

    about 20 ounces plaster of paris (could be portland cement, and I know I'm gonna catch grief for this)
    about 6 ounces bennonite clay (was too lazy to grind it, so I used ordinary cat litter)
    about 10 ounces burned white hardwood ash

    I packed the dry mixture into the base, moistened it, then before allowing it to set, I packed the rest up the sides....seriously rammed it in place aroudn the spacer, and poured in water knowing it'd probably foul up the top layer....

    it seems to have a similar effect to roman concrete (where they used sand and cement with vesuvian ash) to get something with a very very high strenght....this....brick I suppose you could say..has been dropped onto concrete from several feet, has been thrown (by an irritated and irritating roommate) into traffic, where it was promptly bunced all over the road by a semi's tires....and had taken me carving it (a feat in and of's like granite as far as durability) to put in ports for air (which I should have cast in anyway....I made a LOT of mistakes) but it survived longer than did the cans....I did some primitive smelts in it with charcoal and a forced air blast....a crucible made of 3" cast pipe with a nipple threaded on and overtorqued to friction lock it...and it would easily turn the crucible and contents a nice red-orange....

    based on some of the thigns said here, I probably wouldnt' do a full sized furnace with that mix, and I'd probably change some ingredients, but this stuff does have some good durability...sheesh....I had to leave it behind, as I jstu moved, but I'm wondering if it wouldnt' be worth it to try it again with a thicker layer and see what happens.....the materials were cheap and it didnt' put me out too far...but the problem is the short working time.....which also was a problem with the roman stuff....

    it started as an idea to see if I COULD make something like roman concrete fire durable, and it seemed to have worked rather well....I'd probably use this for a shell, and use a commercial refractory for the inside layer......I think part of what helped it work was using as little water as possible, letting it sit forever and a day (let it cure for nearly a week) then slow firing it....first with a small paper fire (this is a SMALL furnace...and I can imagine some of you guys laughing at me...I'm laughing about it too) then moving up to scrap wood, then finally some green oak that we had laying around.....

    used this thing for...counts...nearly 3 years with minimal loss of material......the place that took the most damage was directly across from the burner entry, which finally, after about 2 years dropped out a piece the diameter of a quarter and about 1/2 an inch thick.....

    anyway, I've got to run, but give me a shout back and any and all ideas are welcome....and I hope I caught all the bad spelling msitakes, but then again, I speak fluent I might not catch them all.

  3. #13

    Re: not as bad as it could

    about 20 ounces plaster of paris (could be portland cement, and I know I'm gonna catch grief for this)
    about 6 ounces bennonite clay (was too lazy to grind it, so I used ordinary cat litter)
    about 10 ounces burned white hardwood ash
    :shock: What sized furnace do you have? What are you melting? What temperatures? Pop and bentonite aren't really refractory materials. I do remeber hearing about ash being used to make a crucible for thermite melts... but can't pull many details off hand from memory.

    it seems to have a similar effect to roman concrete (where they used sand and cement with vesuvian ash)
    "Volcanic" ash used in concrete... is a pozzolan... it reacts with calcium hydroxide in cement. Romans mixed it with lime (calcium oxide) and water. I am not sure that wood ash is the same thing. Current day, pozzolans are still used in concrete but they usually come as a by byproduct from coal burning plants. (fly ash)

    Anyway... it flies in the face of everything I would think to use as a refractory... but I am interested in seeing pictures in a separate thread if you have them.

  4. #14

    I wish

    like I said, it was a little experiimental mockup..mostly meant to be used with a propane or mapp gas torch.....not much of anything, really...rather surprising to have vaporized the tip off....

    this isn't the full sized one I'm in the process of right now, and the formulation came about as a lot of monkey-work in trying to figure something out for a quick and dirty to do some small AL in *I've got come pop, I've got some cat litter....and Iv'e got some wood ash...didnt' the romans used to use volcanic ash....huh...wonder if woodash would work? grandpa used to talk about using that sometimes in making a more water resistant cement.....* so I mixed up enough that I thought it'd work, and frankly expected it to spall and blow chunks everywhere.....

    imagine my surprise....frankly I'd like some thoughts as to possibly *why* it worked as well as it did....granted, the shell got hot enough you could light a cig on it, but compared to the internal temp, that was nothing....after I toasted off my brass burner, I decided to try it with some charcoal, and it worked pretty well....this thing was abused to no end...had no lid, left outside in the rain....I did terrible terrible things to this to try and destroy it, because after a while Iw as sick of looking at it...and it just wouldnt' DIE....because shortly after makign it, I actually found the site here, and started reading about actual refractories...and kicking myself saying *HOW CAN THIS WORK?*

    pictures....I wish...I dont' have a digi-cam, and the thing was left at the old place (had to do an emergency move after a roommate tried to kill me) but in the name of sheer perversity, I'm tempted to see if I cant' replicate it on a larger scale......just to see...because according to everything posted and everything I've researched after the creation of should not work..period.....

    about the only thing I could possibly think of is the lye in the hardwood ash had something to do with the properties of it.....but I honestly had no clue what Iw as doing at the time...the next (actual) furnace is being done with 5000F ultra high temp refractory......

  5. #15

    Re: I wish

    l.didnt' the romans used to use volcanic ash
    yes... pozzolonic ash can be found in some volcanic deposits.

    ....huh...wonder if woodash would work?.
    Don't think so. Studies I have seen show additions of wood ash to cement weaken the final concrete, and increase its water absorption

  6. #16


    I know that now, but I was just laying down my train of thought at the time, and figured if I got a hard glassy ball of least it'd be intresting looking and something I might could do something with.... might have something to do with the quality of the ash itself......this is a fine powdery white ash, not cinders and charcoal bits.....mostly jsut mineral salt and carbon... (hardwood ash from my charcoal burns for other metal work, if that tells

    I'm curious enough now about *why it worked at all* to actually make two versions of my with the ultra high temp refractory, and one with this homemade goo, and put the homemade one through abuse and testing....see if I CAN thermal shock the hell out of it, see what temperatures I have to take it to to get it to glass, spall, pop and crack, see what kind of concussive resistance it's got, might be a case of doing everything wrong and getting something useful...but hey....if nothing else, it'll be fun, and that's part of the reason I'm doing this.....metal and research for me gets my geek going...

    btw...slightly off topic, I saw a goregeous (and well muscled in a feline manner) girl with a whiff of ash and smoke around her....she was wearing a shirt with a cruicible on the front, and the words *smelting gets me hot*

    wonder where she got the shirt.....

  7. #17
    You know I’m no expert and I’m new to all of this, but I was wondering today what vermiculite does in order to insulate
    This is what I found I hope others who wanted to know can benefit, and maybe the people who do know can benefit along the way. This book (listed below) is about the best thing I have found on clays. It has it all packed into about 800 pages or so…

    According to A. B. Searle and R. W. Grimshaw “The Chemistry and Physics of Clays”

    Page 157 Chapter: “Layer Lattice Structures”

    Quote: “Another distinct group of Minerals which form large mica-Like flakes are Vermiculites. When heated, these minerals exfoliate in an amazing fashion with an increase in volume up to 100 fold. As a result they are valuable in ceramics for thermal insulation. Vermiculites are mainly hydrated magnesium silicates and may have considerable amounts of Iron and aluminum present.
    The exfoliation in vermiculite is apparently of two types:
    (i) Rapid heating is one cause and presumably the explosive release of water molecules serve to push the layers of the mineral apart. Slow calcinations with gradual increase in temperature does not cause exfoliation and there is little expansion when the vermiculate is of small size.
    (ii) Some Vermiculite exfoliates on treatment with oxidizing agents such as hydrogen peroxide.

    Here is a question what do the authors mean about vermiculites of small size have little expansion? May be they it will not insulate well if it is small? How big should the vermiculite be? I have seen the garden type and it is really small stuff, and I have seen the stuff that our organic solvents come packed in and it is really big stuff. Maybe I should try some of it...

  8. #18
    this is what I’m going to try in my first furnace.

    I am using an old refrigerant 11 drum that is 16” diameter, (changed from a beer keg, I have another idea for it)

    I am using a 12 ¾” sonitube to cast ~ 1 1/14” insulating layer and the bottom will be 3” thick

    This insulating layer will be:

    60% Perlite
    25% Fire Clay
    10% Medium grade sand (quickrete)
    10% old clay pots busted up into pea sized grains (pre soaked in water for two weeks)

    Then the inner 8 ¾” tube for the inside

    The inner blast surface is 2 ¼” thick

    20% Vermiculite (Largest vermiculite mesh I can get)
    50% Fire clay
    20% Fire Brick crushed to medium sand grain sizes (pre soaked in water for two weeks)
    10% old clay pots busted up into pea sized grains (pre soaked in water for two weeks)
    Just a few cups of Play Sand (the finest grade that quickrete makes)

    I know the ratios don’t work out in the inner layer but the sand is just added as extra filler.

    Fireclay in my town is $20.00 a bag
    Fireclay 45 min away in Easton MD is 8.00 a bag…. Cost me 5 dollars in gas, I picked up 6 bags.
    By the way I contacted quickrete and asked them about the purity of their sand this is what they said:
    All the sands are mined from sand deposits from around the nation
    And that the sand is >95.0% pure silica sand, there is however ~ 5% impurities, these are mostly in the form of lime stone, and or iron and residual dust from the air. They told me they wash all the sand with water over an over to get out and organic stuff because over time it reacts with and destroys Cement when mixed with it. They also said they have to get the play sand as close to pure silica sand as possible and as clean as possible to eliminate dust for OSHA requirements.

    I will let everyone know how it goes when I fire it...


  9. #19
    Administrator Site Admin Anon's Avatar
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    If you have all those good refractory ingredients, get rid of all the fluxes in there. Vermiculite has lots of fluxes in it (perlite does too, but perlite melts higher, and usually doesn't cause problems in bronze-capable furnaces). Old clay pots aren't great either--a typical clay body isn't good much over 2000 F. Medium grade concrete-mixing sand is both more expensive and less pure than play sand--still more fluxes. I'd try equal parts play sand, fireclay, and perlite for the hotface (you could throw in some firebrick grog as well, but crushed into pea-sized pieces instead of dust). For the insulation, either use loose perlite or loosely-bonded perlite (probably 33% fireclay, 66% perlite, or whatever is on the verge of not sticking together). By the way, the inner hotface only needs to be 1" thick at the most--the other 2 1/2" can be insulation.
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  10. #20
    Senior Member Rugerdude's Avatar
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    I just built my first furnace and fired it. I used:
    1 shovelful of perlite
    2 shovelfuls of georgia red clay
    2 shovelfuls of whitish sticky clay I found in my backyard (guessing its Kaolin)
    2 1/2 shovelfuls of sand
    some water
    mix it all up
    super strong and insulates pretty good especially if it was invented by a 14 yr old :P
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