I have a large gas forge with a 1" hybrid burner. I have 3 layers of 1" insulation and ct 100 coated. I find that the kaowool is disintegrating after running for a long period of time, 5 hours flat out. Don't know if this is a normal problem or am I over cooking it. The inner layer only.
Thanks for any suggestions

Put on some pictures so we can have a look.

You should cast over the ceramic blanket with a castable refractory such as Kast-0-Lite.  This will give you a good tough, long lasting interior that you can then paint with an Infrared Reflective product such as Plistix, Metrikote or ITC-100.

I actually had similar issues but mine was flux related, I am going to line my new one with 2 inches of Mizzou ( castable )

Thanks for the help, with the refractory lining is this straight cement or do you add something like vermiculite to it.

It is a refractory. Using that to keep the inswool/koawool covered not only prolongs its life, it will prolong ours also. Breathing that stuff is not good.

Castable Refractory is not Cement.  Kast-0-Lite is a light weight, insulating castable refractory.  Check out my web-site for more information.

If your forge is undersized for the hybrid burner you could be exceeding the temp rating on your kao-wool. A standard 3/4" T-rex burner is good for about 500 Cu/inches, and a really good hybrid burner will burn hot enough to damage the Kao-wool. You also might not have used enough ITC100 to stabilize or rigidize the Kao-wool. Bubble Alumina is also a very nice high temp refactory that stands up to abuse and flux very well. Apparently a bunch of the guy making a lot of pattern welded steel have been switching to the bubble alumina because it stands up to the flux so much better...

Thanks for your replies, I have enough Kaowool left to put in another layer and then coat again with ITC 100. I do not believe that the coatings I have been using have been very thick. When coating do you do more than 1 coat of of the ITC product. I have also purchased a refactory mortar called fondu and was going to mix this with the vemiculite, the specs on this rates it upto 2350 degrees f.
Kast o lite is not readily available in Australia so I might try the fondu mix first and see how I go.

Thanks for everyones generous information.