Quote Originally Posted by djed View Post
Looked online and found a suggestion to add bonding agent (looks a lot like white glue) to the water that I mix with the plaster. I also kept the mix closer to the original water mix ratios resulting in a thinner plaster mix. The mix could only be added to the bottom of the safe wall since it would run out otherwise. After a few days of dry time, the insulation now seems to be holding and not shrinking/cracking. I hope this helps someone in the future tackling this same issue.

You mean PVA as the bonding agent?