I have been reading here for a while but this is my first post. I recently made a propane forge from a helium tank. I lined it with 2" of kaowool then did two layers using a refractory morter I bought from my local hardware store. It was red devil rated for 3000 degrees. I put it on over the last several days half a coat at a time (gravity was my enemy.)a couple of times I baked it in the oven at 250 for about an hour. Including after the last coat. It then sat for about 24 hours before I stuck the burner in and tried to fire it up. The burner was only on maybe 15 secs and the lining bubbled really bad. I assume I just didn't let it dry enough. Any thoughts or input? I am going to attach a before and after. 

It needed a longer dry time between layers. Did you dry it i the oven every coat?

Cement doesn't really "dry" it hydrolizes which means the moisture and the binder forms a compound that locks it all into a solid whole. I don't know about the product you're using but assume it comes ready to apply. Yes? 

It's also a mortar, NOT a refractory liner. Mortars even refractory mortars stick masonry together, fire brick in a furnace or fire place for example. A refractory liner is designed to withstand direct contact with the fire itself, hence the term "Flame Face." These are two different jobs and often not interchangeable.

My second thought is this mortar isn't going to work as a forge liner but I could be wrong. I'm good at that.  

Frosty The Lucky.

I used Meeco's as well, it seems to be holding up well but I haven't been forging long at all.  It did the same thing to me, it bubbled up on a very thin coating, I broke the brittle pieces of it off and its holding up fine the wool underneath was not exposed, and I haven't had any loose wool particles floating around, though the meeco's seems to be very delicate it holds up to the heat really well I think. (not an expert) just built my first forge(s).  I didn't get bubbles that big at all, I really did maybe like a 1/16" or 1/8" coating on my wool.  I'm guessing you did a thicker coat.  Material says it has no set/cure times so I assumed as well just fire up after I coated, I did and my forge interior looks relatively good (I think).  Meeco's is cheap, easy to apply and so I just keep an extra half gallon around for patching any cracks and what not, I will be coating it with ITC 100 HT with hopefully great success and no catastrophic failures.

Add - If you want to see my forge set up, I have a thread in the forges section called "Gas Forge Heat" I was having issues getting temps up but it was a burner construction error, and have it operating well now, thanks to the advise I got here.

DRATS I just realized I forgot to welcome you to Iforge! Welcome aboard, glad to have you Dusty guy.

Check out Wayne Coe's site, he has all the materials you need in small quantities for reasonable as well as good plans, burner designs and is a very knowledgeable and helpful guy.

Frosty The Lucky.

Nub, you would not know if there were fibers floating around.  They are so small you can't see them, just like people didn't see asbestos particles floating around.

Let me know if I can help you.

Wayne

Good to know obvious oversight on my part

Well I started picking away at the spots that were bubbling so I could redo the second coat and then figured it was probably just going to bubble some more. So I just took it outside and fired it up. A bunch more from the second coat bubbled up but seems fine now. First coat held up great. I had every intention of buying some satanite to line it with but then I had some time off unexpectedly and decided to just go with what I could get locally. Thanks for the input I will have more questions before long I am sure. 

Have you ever seen where someone tried to cast a thin coat of concrete over an old slab?  It will flake off because there is no adhesion between the two layers. Same thing happens here.  Just do a 1/2" thick casting and use the proper product.  I like Kast-0-Lite.  It is a light weight, insolating, flux resistant castable refractory  specifically made for this purpose and better than Santanite.

Let me know if I can help you.

Wayne

Frosty is exactly right. I had the exact same thing happen. Turns out that I put a second layer over top of a layer that was not completely cured. I had to chip off all the bubbled and loose stuff and do it again. Wasn't a big deal just an exercise in patience