Insulation for Fireproof Safe

[Arcade Al]

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?

[Chubby]

PVA will help to stop such things cracking. You don't need much.

We used to add it to the concrete in which floorsafes were installed. When testing concrete samples it was noticable that those with PVA added were a little bit tougher than the others.

[djed]

This is the stuff I used:

https://www.homedepot.com/p/Quikrete-1-Qt-Bonding-Adhesive-990214/100318541

I also brushed this on the area into which the plaster mix was going to be poured.

[Chubby]

From memory we used to use a jam jar full of the stuff for 1 bag of cement (50Kg). That seemed about right. The mix we used to use was 3:1.5:1 by volume of 15 mm granite chips, sand and portland cement. We kept water to a minimum. I think it was around 20 litres maximum for that, but with all such mixes, that assumes your sand to be dry, which it rarely is. The minimum water was to ensure maximum density. Of course with fire resisting material you don't need density, quite the reverse.

One problem is to make sure that the material you are using won't react with the steel and destroy it through corrosion. How you protect against that, I have no idea. I don't think plaster is particularly aggressive.