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  1. #1
    Join Date
    Mar 2016
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    46
    Country: United States

    Default Insulation for Fireproof Safe

    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

  2. #2
    Join Date
    Oct 2009
    Location
    Cleveland, Ohio USA
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    1,433
    Country: United States

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    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.
    Attached Thumbnails Attached Thumbnails IMG_20180328_194228270_BURST000_COVER.jpg   IMG_20180328_194152561.jpg  

  3. #3
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    Oct 2009
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    Cleveland, Ohio USA
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    Default

    Maybe this pic is better
    Attached Thumbnails Attached Thumbnails IMG_20180328_202351875.jpg  

  4. #4
    Join Date
    Mar 2016
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    46
    Country: United States

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    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.

  5. #5
    Join Date
    Jul 2014
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    266
    Country: Germany

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    You could look through safe patents for fire insulation stuff.

  6. #6
    Join Date
    Sep 2004
    Location
    Devon UK
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    Country: UK

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    Quote Originally Posted by Cepasaccus View Post
    You could look through safe patents for fire insulation stuff.
    The alum was the active ingredient - the rest was normally just absorbent filling.
    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.

  7. #7
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    Mar 2016
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    46
    Country: United States

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    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.

  8. #8
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    Mar 2016
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    Country: United States

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    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.

  9. #9
    Join Date
    Nov 2014
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    Bulgaria
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    686
    Country: Bulgaria

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    Fill the void with more of the same.

  10. #10
    Join Date
    Mar 2016
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    Country: United States

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    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.

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