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Mixing castable refractory and fire clay?

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Hi.  New here and I know enough to be dangerous, which includes knowing that I don’t know much in the big scheme of things.  I’m building a gas furnace that will be lined with 2 inches of ceramic blanket density #8 that I am going to cast a 1 inch refractory over.  I’ve got some Girtech Firecast, but I’m a little shy of what I need, and want it to go a little farther.  I’ve got some ground fireclay, and I’d like to get some opinions on adding some ground  fireclay to the Firecast castable to get more refractory in the end.    I am concerned it might compromise the strength of the refractory, but also think that there is probably a reasonable mixing ratio that it would still work out.  Thoughts?



-Trey in Spokane



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Welcome aboard Trey, glad to have you. If you put your general location in the header you'll have a much better chance of meeting up with members within visiting distance. We aren't going to remember you mentioning it in one post after we open another one. Honest, we're blacksmiths not mentalists.

I hope you didn't already buy it. A quick search shows it to be refractory CEMENT, not a fire face refractory. It is meant to cement things together like firebricks. It is unlikely to survive long in direct exposure to a VERY chemically active propane flame. 

The current consensus on Iforge for probably best castable refractory is, Kastolite 30-li a water setting high alumina bubble refractory rated to 2,600f constant. The bubbles are evacuated silica spherules that are intended to make it physically lighter but also slow thermal conductivity. Insulates. Better for our purpose it is calcite bonded and being high alumina it is very resistant to caustics like molten borax at forge welding temps. It is GREAT stuff.

I believe but haven't checked there is a "Distribution International" in Spokane, if so give them a call, it is where I buy all my refractories and the Anchorage store carries Kastolite as well as Morgan Thermal Ceramics, K-26 insulating fire brick which is rated at a solid 2,600f and is borax based flux resistant. 

Frosty The Lucky.

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Frosty, you seem to be a wealth of knowledge with a knack for explaining idea to the uneducated (me).

You brought up a good point about refractory cement. I also use fire bricks (rated for 2700°F) for the base of my furnace. 

Why would someone want to cement fire bricks together vs just stacking them? Wouldn't all the expansion just crack the mortar anyways?

After all the repeated firings of my furnace the bricks have probably moved over an inch. I use a nice layer of super fine silica (aquarium sand) on the bottom of my furnace for that reason and to protect my fire brick from spills and whatnot.

Actually, the ones I use are called insulating fire brick rated for 2500°f.

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Thanks, I'm just passing the benefits of my mistakes along so hopefully you newcomers will make new fresh mistakes we can all learn from. Refractory cements and mortars are for fireplaces and ovens, furnaces, etc. that don't reach temps nearly as high at a well tuned propane forge. Good mortars have COEs very close to firebrick hard or insulating so any difference is absorbed by the brick or they wouldn't stay stuck long. Places like fire place hearths and large furnaces don't heat up as quickly as a propane forge. My forges come to forging temp in maybe a couple three minutes and welding temps in about 5. 

Standard IFB (Insulating Fire Brick) crumbles at temps above about 1,800f and rarely last two firings in my too silly large variable geometry shop forge. Morgan thermal Ceramics K-26 IFBs are rated for a sustained 2,600f and will take a bit more. They are also very resistant to molten borax based welding flux. The old hard firebrick dissolves in contact with molten borax in any form.  

ITC-100 has changed it's formula in recent years and is now a GOOD kiln wash, if you can find it for a reasonable price. It contains zirconium flour in a proprietary binder. Zirconia is just a tad softer than diamond and has a vitrification temp around 3370f which is WAY hotter than an oxy propane burner can generate. It has low conductivity and is chemically pretty inert. Put all that together and it serves as a VERY good final layer of armor for the flame face of our forges. The low conductivity means it absorbs energy from the burner but doesn't conduct it to the next layer very fast so it gets REALLY HOT and because it is such a poor conductor has to shed it in the best manner available, as IR radiation back into the forge chamber.

Kiln washing a Kastolite 30 lined forge will convert it from an easily yellow hot chamber to an eye searing bright high yellow/white temp chamber. On top of this primary goodness in a propane forge it laughs at molten borax fluxes and is an almost diamond hard coffee cup hard fame face. (yeah, I know I used the same adjective twice in one sentence, sue me I'm a blacksmith:P)

An IFI member in the Nederlands,Marten, developed a very good home brew kiln wash that with modifications could make a good flame face liner. He uses approx. 3% bentone (a variety of bentonite) to 97% zirconium phosphate in a tooth paste +/- consistency as a flame face wash to great effect. I've made a version and it's been living happily in my latest NARB forge.

I gotta stop, or I'll go on for ever but that's the basics oh hard inner liner and flame face kiln washes as I do it.

Frosty The Lucky.

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30 minutes ago, Frosty said:

(yeah, I know I used the same adjective twice in one sentence, sue me I'm a blacksmith:P)

I'm more concerned that you said "hard fame" when you meant "hard flame".

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Uh huh, you'd pay me if you heard me sing. . . To stop that is.

Not to change the subject but after watching some knapping videos I came back to find my inbox FULL of blueprints!

Sorry, I'm just feeling a little giddy right now.:)

Frosty The Lucky.

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Posted (edited)



Is this the product you are suggesting?  I want to double check before placing the order.  Thanks for your time on this.

HWI Kast-O-Lite® 30 LI G 

[Commercial link removed.]

Also, I found a burner design a while back that I used in a small forge for knife making that tapped into a black iron pipe T using a MIG welding tip as the gas nozzle.  Thinking back I recall that it was called the Frosty T.  2+2 being 4 and all, I’m thinking that must be your design.   Very cool man, very cool.  I made a larger burner with that design for my furnace I’m itching to fire up once I get the refractory squared away.



Trey in Spokane


Edited by Mod34
Commercial link removed per TOS
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That's the stuff Trey. When you make your liner the walls and roof don't need to be more than 3/8" thick though a number of guys like 1/4", it's really tough stuff.

Do NOT forget to rigidize the ceramic blanket! Encapsulating the fibers is more important to control the breathing hazard than making it stiffer. Though stiffer makes things easier.

Yeah, I'm THAT Frosty. :unsure: <sigh>

It's my pleasure. 

Frosty The Lucky.

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