Castable core ingredients and recipe

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Castable core ingredients and recipe

Postby Prescott » Sat Sep 28, 2013 1:46 pm

Holy guacamole! At long last I have located fire clay in Maine, and arranged shipping details from 200 miles away with a local potter.

SSSSSOOOOOOOOOO, now that I can create my own castable mix, let's talk ingredients and ratios!

If we relax and keep things simple, I can see using my vermiculite in a 1:1 ratio with "the other stuff"' and then, in the same vein, having "the other stuff" be a 1:1 ratio of fire clay to fire cement.

Part of why I went bulldog-tenacity for the fire clay is I already have two 50# bags of heatstop50 and was determined to use the stuff up. It's also a cheaper than castable refractory cements, plus i just really liked the idea of coming up with a tough and affordable mix to share with the community!

Once we dial in ingredients, looking to measurements is next! So instead of a little thinner as with the castable refractory products, I'd be looking at a four inch wall, back to Matt's basics, no?

Huge sigh of relief here, and now I can focus on getting some more prep done. I'm down with the thrill of the chase and all, but it feels good to have lined things up (of course Monday I need to finalize the details, may everything go smoothly!)

Here's to an incredible autumn day, or at least here's to you from an absolutely spectacular day in DownEast Maine~p
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Re: Castable core ingredients and recipe

Postby Prescott » Sat Sep 28, 2013 1:48 pm

Remembering to check "notify me" is taking some practice... :roll:
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Re: Castable core ingredients and recipe

Postby matt walker » Sat Sep 28, 2013 4:59 pm

Sounds good Prescott, glad you found your materials. I believe that your mix of 1:1 clay/cement will make a really strong material. Can't wait to see how it works for you.
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Re: Castable core ingredients and recipe

Postby Rhett » Tue Apr 08, 2014 12:15 pm

Hey Prescott, about that vermiculite, man my mix just devoured the stuff. No matter how much I used it just disappeared into the mix without seeming to add volume. At the end I used 2:1 verm:clay and it looked like I should have used 4:1! I don't know if perlite behaves the same way, but perlite looks to have a little more loft or body or something. The end result with my build which you can see in my post history in videos is deep structural cracking. Basically it broke into three or four large chunks that are somewhat stable when interlocked but need patching ASAP.

Maybe I did something wrong and vermiculite is all good. Just sharing my experience.
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Re: Castable core ingredients and recipe

Postby Rhett » Tue Apr 08, 2014 12:24 pm

Matt, did you ever experiment with adding sand to your formula? From what I have read about cob sand is the part that makes it strong. The more sand the stronger the cob, the more clay the more cracking. Sand should be able to withstand the high temps so is there some reason not to use it? Does it react badly under thermal shock or reduce insulation qualities of the mix?
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Re: Castable core ingredients and recipe

Postby matt walker » Thu Apr 10, 2014 4:34 am

Rhett, I use sand often, but in the core I was going for insulating properties and I figured the Perlite sorta took the place of the sand, only lighter. There is a lot of dust in the bags of Perlite I use, and it seemed like it was sand-ish enough, if that makes sense.
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Re: Castable core ingredients and recipe

Postby Prescott » Thu Apr 10, 2014 6:59 pm

Hi Rhett. Hope your pieces of your cast stick together. It's nice to be thinking about this stuff as I'll be casting another core in the fall. Partly because I am making a bigger system, partly to improve on the existing system and methods, and partly because it is fun!

I am tinkering with ideas and mixtures, pretty sure I am going with a similar mix but instead of fireplace mortar, looking into castables and other high temp concretes etc. The fireplace mortar can take the heat, it just doesn't have any structure. My feedtube is a little beat up (partly me jamming stuff into it and partly due to not the best packing job when I cast [part my six year old helper and part first go around with this stuff!]) but the burn tunnel and heat risers are doing splendidly, better packing during the cast and just so little traffic if any at all.

I have tons of vermiculite left so going to go with it, I like ho my core behaves for the most part. I think I am going to beef it up a little size wise as I won't be cobbing it (again, like the first cast) and just excited that folks are going ahead with their own projects and sharing the info. Like Matt, I'll be skipping the sand for insulative purposes, but know a guy making his own castable bricks and tweaking his mix, he's amazed at how the mix responds to the inclusion and ratio of sand. More than I am involved with...

Spring is finally melting the snow off here down east, brutal winter but I am amazed at how little wood I burned! Winters won't be this bad for a while, at least I sure hope so...

Keep building and sharing
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Re: Castable core ingredients and recipe

Postby freedomlives » Wed Apr 16, 2014 10:42 am

a bit of wisdom from that Building with Lime Book (I think that's where I read it).

At least with lime as a binder for an aggregate (sand, or in this case perlite) you want the lime to fill the space in between fully, but not much more-- just like with clay, lime on its on will crack when it dries.

For sand-lime plaster there is a simple test (for those who want an empiracal way of mixing). You first dry the sand in an oven (since it often is wet from sitting outside), and then you use (in the case of sand) alcohol, and carefully measure the amount of alcohol that can be added to a given volume of sand. e.g. Fill a 100ml jar with dry sand. Measure into another jar 100ml of alcohol. Pour slowly the alcohol into the sand until no more alcohol can be added. Then measure the remaining alcohol and subtract to get how much you poured out. (e.g. 65ml remain, so 35ml got poured into the sand). This last figure (35ml) is how much free space there is around the sand particles. Then you just create a ratio-- for every hundred liters of sand, add 35 liters of slaked lime, and maybe push it to 40 to make a "fatter" more spreadable mix. Alcohol is used, if I remember, because it doesn't swell clay particles that may be in the sand.

This test for how much clay to add to perlite would not work though, since the perlite is very porus to liquids but not to clay. So you might get something like 90ml of alcohol per 100ml of perlite when there is only room between perlite particles for 30ml of clay.

Of course, the other way is just to make a bunch of test mixes.
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