Shielding Kaowool with Mortar

[graymachine]

I am building a new furnace out of a keg, essentially following Brian Oltrogge's FIRE-KEG build. Instead of making the walls out of castable refractory as he did, I plan to use 2" kaowool and coat it will about 1/2" high temp mortar to shield it (and prevent any nasty health effects from heating the kaowool). I plan on using just a simple furnace mortar, the type that you pick up at a big box store, but I'm unsure how well it will work being only 1/2" thick. Does anyone have any experience with that? I know that Satanite would be the best option, but I would prefer to avoid that if I can since the cost plus shipping would be pushing my budget. Thanks for any insights!

[Buzzkill]

It might work.  I tried this in a small forge using cement that was supposedly rated for 3000 degrees F.  However, once the forge got up to temperature, this stuff turned into a semi-liquid and would stick to the steel when I bumped hot stock into the lining.  After it cooled it was hard and smooth almost like glass, but the next time I ran the forge it happened again.  On the portion of the lining directly across from the burner the cement had been pretty much blown away where there was direct flame impingement after 2 or 3 firings.  I believe the brand I used was "Do-All"  by Durst, and others may react differently. Mortar/cement is designed to hold pieces together, not to really provide a structure in and of itself. Maybe you'll get better results than I did, but that was my experience.

[David Durman]

I don't know why it  is showing two different screen names for me. Anyway, do you think that using chicken wire or woven wire mesh as a rebar frame would help?

[Buzzkill]

I didn't have any problems that I thought would be solved by a mesh.  The cement I used just didn't stay solid at those higher temperatures.  I was using a 3/4 inch Frosty T burner, and while it performs well, I seriously doubt I was approaching 3000 degrees F in the forge.  It stuck just fine to the ceramic blanket, but when it turned semi-liquid the force of the flame and gravity resulted in some bare, or nearly bare, spots on the blanket.

On another thread I saw someone who claimed that the stuff they bought at one of the big box stores is still working fine after a year.  Not sure what brand he was using though.

[phabib]

I built a gas forge doing just what you describe.  The rammable refractory I put over the kaowool held up just fine and since it was pretty thin didn't suck up a lot of heat to get up to temperature.  This would be a lot more useful to you if I could remember the name of the material I used, but I don't.

[Dodge]

I coated ceramic wool (Inswool rather than kawool just because it was sold locally) with a refractory mortar from AP Green and only using maybe less than 3/8". Its rock hard and after 5 or 6 years I have never had to repair it due to fractures. Heats quickly but I have always wished I had made it thicker and would if i did it again

[Frosty]

You're seeing the different between furnace refractories and furnace MORTAR. Even if it's rated for 3,000f. MORTAR is intended to stick bricks together NOT survive direct flame contact, it is NOT a flame face safe material.

Phabib and Dodge used castable REFRACTORY and their forges have operated for years. HMMMM? 

Dodge: I only write Kaowool because that's what EJ Bartell, the local HVAC guys carry on the shelf, I can write it without thinking it's almost a muscle memory reflex. There are lots of ceramic blanket refractories of equal or better qualities.

Guys the fibers from refractory blanket aren't toxic, no more than any unglazed coffee cup. The breathing hazard is the result of HEAVY and PROLONGED exposure. Asbestos took decades of daily exposure to cause mesotheloma in a few % of folk who worked with it. Don't let the TV shyster commercials trying to sucker YOU into giving THEM a % of any class action suit you may get a share of. They are NOT lawyers and they are as honest as ANY mass marketer.

I'm not saying you should use it to breath through I'm saying don't panic it takes a lot to bother you so if you avoid exposure when reasonable you're golden.

The short formula for a gas forge liner: two each layers of 1" 8lb. ceramic blanket refractory. Rigidized to encapsulate fibers and make it reasonably hard for durability. About 1/2" layer of a high alumina cast refractory, once set and heat cured, (if necessary, see the directions) an IR re radiant kiln wash similar to but not necessarily ITC-100.

Contact Wayne Coe for small quantities for reasonable $. If you don't need 50lbs. why but a bag?

Frosty The Lucky.

[Yuppiejr]

15 hours ago, Buzzkill said:

I didn't have any problems that I thought would be solved by a mesh.  The cement I used just didn't stay solid at those higher temperatures.  I was using a 3/4 inch Frosty T burner, and while it performs well, I seriously doubt I was approaching 3000 degrees F in the forge.  It stuck just fine to the ceramic blanket, but when it turned semi-liquid the force of the flame and gravity resulted in some bare, or nearly bare, spots on the blanket.

On another thread I saw someone who claimed that the stuff they bought at one of the big box stores is still working fine after a year.  Not sure what brand he was using though.

That was me:

http://www.menards.com/main/heating-cooling/fireplaces-stoves/fireplace-blowers-tools-accessories/refractory-cement-1-2-gallon-buff-color/p-1444439439282-c-6845.htm

Mine is coated in ITC-100 as well (purchased from Wayne Coe). 

My approach is probably more the "if it's stupid, but it works..." variety than the correct application of refractory, but my little forge heats up fast and makes metal hot so I'm not inclined to change it until I need to.

 

[Dodge]

To be fair, the refractory mortar I used was an industrial product; not a big-box-store home wood stove patch. Yes it is considered a mortar and I did have issues tyring to us as a cast floor (It blistered a bit) but as a ceramic wool coating, it has performed beautifully. Probably because it is also billed as a refractory patching material. It has fibers in it that haelp reduce cracking. If fact its called "GreenPatch". There is a thread specifically about it somewhere in this forum...

[Frosty]

If it works it works, you just don't hear complaints about things that work. To be honest not all mortars are poor performers as a hot face they're just not common.

GreenPatch makes refractories for industrial applications and makes it part of the name. I'll bet the product is made to patch furnaces but CAN be used as a mortar. I used GreenCast 94 in an earlier forge but discovered it has zero insulating qualities and a high specific heat so it made a serious heat sink. I just picked it out of a book so it not working in my app isn't a reflection on the product. However, it has mortar as one of it's applications too.

In fact Kastolite 30LI mentions it being used as a mortar, it's just not it's primary application.

Picking a product that's made to be mortar as it's primary function really ups the odds it'll make a crummy hot face. (Literally crumby)

Frosty The Lucky.

[Buzzkill]

I had used Greenpatch 421 on another project and it seemed to hold up to the direct flame fairly well.  However, my assumption that if one high temperature refractory mortar works then another one should as well didn't turn out to be accurate.

[Frosty]

Ayup, sometimes things just don't do what it sounds like they should, been there done that.

Frosty The Lucky.