Im wanting to make a fireproof storage box for datasticks, cash, documents, etc. Internal dimensions only need to be about 15"x15" square by 12" deep.

Im thinking a regular box built from firebrick, then lined with 2 or 3 layers of sheetrock, and then that held together with a layer of fire-resistant tape or wrapping.

As for the lid, I might get some sort of metal lid like you would find on a city street over a water access cover, and covering it with the same layers of fire-resistant material.

For added protection, items inside could be placed inside a Nomex bag to add insulation, and protect against anything that might fall into the vault that could damage the items.

that will be very heavy. But otherwise, looks good

buy one.

you can get them for $40 now...

I wouldn't trust a DIY job to store valuables.

Keep in mind that the box would also need to be sturdy enough to be able to withstand having the building collapse onto it, which is likely to happen.

I would think that a heavy steel safe/box lined with firebrick would be sufficient. As long as there are no gaps/holes the firebrick would be practically impenetrable by heat.

asbestos. lots of it.

Be sure to use light weight firebrick. Ceramic wool blankets are good also.

In order to set the record straight, I have created a new webpage to deal with the facts regarding the thermal properties and performance of Ceramic Fiberboard, Ceramic Blanket, Lightweight Insulating Firebrick, and Standard Dense Ceramic Firebrick(the stuff Steel Mills line their furnaces with).

Ceramic Blanket, Ceramic Fiberboard and Lightweight Insulating Firebrick are classified as Insulation, while Dense Ceramic Firebrick is NOT.

The insulating refractories have Low Thermal Conductivity, which means heat does not readily pass through them. The heat is reflected back into the chamber instead, creating a super efficient firebox.

Dense Ceramic Firebrick on the other hand, has a High Thermal Conductivity, which means heat readily passes through it, instead of "insulating" the chamber, it act as a heat sink, absorbing heat and radiating it off through the shell. Dense Ceramic Firebrick, by it's very nature, ROBS a Forge of valuable heat. It's cheap and a very poor choice as a liner material for walls and ceilings.

http://www.diamondbackironworks.com/page/page/4707712.htm

And for the door you should build an insert step that makes a 90 degree in the gap. In other words a raised rectangle or square that is filled with fireproofing that fits snugly into the safe's storage cavity.

Thanks for that post. I would have been pissed if I wasted extra money on dense brick.

I think the store-bought ones have a special chemical that expands when it is heated, so it takes even more energy to heat it up. The drywall is a good idea; plaster takes energy to dehydrate it (drive off the water that was mixed in when it was cast), so it will resist fire better. Just remember that your weak spot is going to be the gap between the lid and the box.