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Castable Refractory Cement

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Cement is an adhesive and products sold as 3,000f castable refractory "Cement" are notorious for having short lifespans as a flame face.

Without knowing how you were constructing your melter I can't make suggestions without guessing. There are too many people on IFI, some with zero knowledge or experience so I take it as a duty to steer them away from dangerous mistakes when possible. 

Kastolite 30 has a working temp of 3,000f, is chemically resistant and is a decent insulator. The bubbles (evacuated spheres) melt out and go I don't know where the voids left allow the refractory to shift and vent moisture during rapid thermal cycling which makes the liner last longer.

There are other products that work very well, I have some GreenCast 97 that is a seriously high end 97% high alumina castable refractory but it's dense and heavy with about the same insulating properties as an equal thickness of limestone. (R1 = 12" of limestone)

Frosty The Lucky.


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  • 2 weeks later...

I looked around quite a bit about the best way to line my Devil Forge furnace, I settled on using the rigidizer that came with it, then tonight after I cure it, I'm going to do a layer or two of Kast-o-lite 30 and then after curing that I'm going to finish with a layer of ITC-100HT as the flame face.  Everyone says the ITC is nutso expensive and from what I can tell, they're right, but I did find this on Amazon for 25$ a pint which is by far the cheapest I've ever seen it. As far as I can tell, yes it's the real thing:   (Remove commercial link)


Good luck and let us know what you end up doing!

Edited by Mod30
Remove commercial link per TOS
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I applied Kastolite last night after drying the rigidizer, man it was more difficult to work with than I expected.  I don't even know what I expected, but it was more like, well, an actual castable mortar than a "paint like consistency".  I got it all in though, and it set quite rapidly.  I made a little "tent" out of wet towels to keep it damp (this is central FL as it is, so not much chance of it being too dry anyways) and left it open at the top with a heat lamp shining on it.  Checked it this morning, seems to be hardening quite well.  I'm going to leave it drying another day or so and then fire it up tomorrow, then apply the ITC and hopefully should be good to go after that.

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Haven't read any of my experiences working Kastolite 30 have you? 

You need to stop thinking about mortars, they are not appropriate in a propane forge. UNLESS you're making it from masonry. How in the world  did you connect Kastolite with "paint like" consistency?

It doesn't need a heat lamp unless it's dropping below freezing at night. 

Frosty The Lucky.

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May I ask why not?  I am eager to learn more.  Why is a coating of mortar over the rigidizer not appropriate?  It seems to be hardening quite well from what I can tell?

Or is just painting over it with Satanite a better option?


I was using a heat lamp because the instructions state "The best results are achieved at curing temperatures of 90-110F."


It also states "Typical dryout schedule for a single layer, 9"
(229 mm) thick or less:
ambient to use temperature 100F (56C) per hour"


Am I misinterpreting this or are the instructions just overly cautious?

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This is probably an over-simplification, but Kastolite has 2 schedules for all practical purposes.  The first is the curing stage.  This has nothing to do with drying per se.  In fact it's best done in high humidity, but will happen faster with the temperatures you listed.  However, most of the time if you apply heat you're also reducing the moisture in the area heated, which will make Kastolite weaker.  

After the curing stage is complete (at least 24 hours, but up to a week) then you can start stage 2.  That's when you drive off the excess moisture slowly.  You don't want any remaining water to flash to steam, which could cause mini-explosions in the material.  Then it's just continuing to raise the heat and duration of heats until you get to operating temperatures.  According to the spec sheet for the material it's somewhat weaker in the mid range of its operating temperature than it is after being fired at high heat for a while.

Satanite is different.  It is a clay based material that does indeed dry out rather than "cure" or "set."   That one you paint on in thin layers, dry, repeat until you get the thickness you want.


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21 hours ago, Samael said:

Why is a coating of mortar over the rigidizer not appropriate?

Are you using mortar or Kastolite 30? They are two entirely different things, neither will serve to do the other material's job. 

Part of your trouble is not having a handle on the jargon. There are specific terms for materials and processes in any craft/trade that allows people to communicate without having to explain what they mean constantly.

Kastolite 30 is technically a refractory "concrete," an aggregate gradation bonded with a calcite "cement." The stuff in the sidewalk is an aggregate gradation bonded with Portland cement. Both are a concrete but worlds different in application and characteristics.

Mortar is the stuff between brick in a wall and is a gradation of fine to no sand and various cements. 

Kastolite 30 is hard to smooth because the aggregate is crushed and the sharp angular particles "key" together like jigsaw puzzle pieces, they do NOT slip past each other easily. This provides voids between particles that allow it to shift during thermal cycle expansion and contractions and not break up. It also allows moisture to escape without building pressure beyond the yield strength of the material. 

The bubble in Kastolite is hollow silica spherules that take the place of some of the sand in the aggregate. Being smooth spheres the calcite cement coats them evenly all round and when the refractory liner gets hotter than IIRC 1,800f or so the silica melts and is absorbed into the liner leaving vacuum (filled?) void. I'm not so sure they remain evacuated but maybe.

Kastolite does NOT spread, paint, etc. on. You have to more or less force it to your will, I discovered spanking it with the trowel until the fines have risen to the surface left a pretty good surface. Better still was to cast it in sections with the finish face down on a smooth surface lined with something super duper non-stick. Wax paper was only okay, Saran Wrap worked better but I ended up burning it off. 

Grease similar to Crisco worked well but I found ramming it in place to get a smoothish finish face drove some of the aggregate through the grease and it stuck to the form. I had to take the sander to the form to clean the Kastolite off it.

I've described how I mix and use Kastolite in another section and have already repeated too much now.

I'm not trying to bust your chops but you'll start picking this up much faster and more clearly if you start using the right jargon, terms for materials and process are important. 

Frosty The Lucky.

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I ended up doing something similar to what you mention with spanking it with a trowel.  Thanks for the jargon clarification.  I fired the furnace to full after heat cycling it on low a few times to remove moisture, and it appears to have set quite well.  It turned a brighter color of white/gray afterwards but no cracking or deforming.  I am going to apply IR reflector and start melting tonight.  


I appreciate the knowledge!  I'm learning quite a bit here.

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