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Does anyone have an idea what the proper mix of alum powder and plaster should be in a fire resistant safe?
Refractory cement would work but is if a different consistency than was originally used.
I’m restoring a safe where the safe bottom was cut out.
https://i.imgur.com/2wwSE5C.jpg
Finally finished making the friction fence assembly. Made a new brass tube and cut in a groove for an internal spring. Fortunately had the correct size gear but it had a large hole that needed filled. Used low temp "Tix" solder for the gear insert also made of brass. This insert needed 2 small internal steps to engage into the slots cut into the tube. This was done with hi temp silver solder. These steps tie the gear to the tube. I annealed the tube ends prior to bending them over so they wouldn't crack. So it is working more freely now. It is important to pay close attention when installing the drive cam onto the dial spindle, making sure the drive cam gear teeth engage into the fence gear. It is possible to trap the fence gear under the cam gear. Tightening the cam in this situation puts undue stress on the low temp solder used. Otherwise there is little stress on that solder joint and it should work fine.
Maybe this pic is better
Looking forward to seeing the fence. I know how badly I burned it so I’m shocked that it could be rebuilt. Amazing work.
On the topic of insulation, gypsum, lime and alum in a 4:2:1 ratio seems like it is not nearly as hard as the original material. The old articles I found called for 4:1:4 but sourcing alum powder is neither easy nor cheap. Still looking for suggestions.
You could look through safe patents for fire insulation stuff.
The alum was the active ingredient - the rest was normally just absorbent filling.Quote:
Originally Posted by Cepasaccus
the alum was sometimes in tin boxes in the fill.
the alum released water in a chemical reaction on heating and the water turning into steam and escaping removed a lot of heat energy from the safe. It wasn't a barrier to anything except heat so the physical strength of the fill was not normally a feature of these fire resisting safes.
I actually found the ratio I referenced in an old hall patent. I also read that the alum was inserted in the mix as large pieces rather than as powder (which is what I purchased). I wasn’t aware of the tin boxes. That still leaves me wondering what they used. I understand these weren’t necessarily meant to be burglar proof but the original insulating material is harder than the mix I created.
Disappointed - the plaster/alum/lime mix shrunk and separated from the safe wall (so that it is now floating as a chunk of plaster in the large hole I filled).
Not it sure which direction I’m headed. Suggestions are welcome.
Fill the void with more of the same.
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.
Quote:
Originally Posted by djed
You mean PVA as the bonding agent?
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.
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.
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.