Greenpatch-421 A 53% alumina, wet, air setting thick patching mortar. This product comes pre-mixed and can easily be thinned with water.
Greenpatch 421 is a product made for repair of forges and foundries and is great for sealing Inswool/Kaowool insulating blanket.
I have personally used this product for sealing Inswool on the forges I make. It is my opinion, that this is a superior product to Satanite in this application.
Forge repair. It is rated to patch/repair existing forges or foundries in up to 3 inch thicknesses. Curing is recommended and more than one layer of this product is recommended.
Manufactured by Harbison Walker
If using Greenpatch 421 to seal Inswool/Kaowool you can thin it with water if needed (you may want to thin if your Inswool/Kaowool tears when applying).
I apply it with a paint brush. A thin coat for the first coat is fine. I let it dry overnight, bring your forge up to dull red and let it cool. This cures and hardens the Greenpatch 421. Then coat again and repeat the curing process.