Mounting a safe in post-tensioned foundation

[SQLGeek]

Has anyone done this? I need to get a safe before my collection grows much more and figuring out mounting it in a post-tensioned foundation has been my big hold up.

I've done some reading on this and the answers seem to be all over the place.

 

[F350-6]

To be 100% sure, x-ray the concrete. That's what they (professionals) do before the cut it.

Looking to save money? You can try looking at the edge of your foundation, measuring where the straps are, measuring the inside, and double checking with one of those magnetic stud finders, but there is other steel in the concrete too.

If you have access to thermal imaging, you might be able to warm the concrete for an extended period so the steel strap gets warm too, then throw a bag of ice on the concrete for a bit so it cools quicker than the steel and figure the location that way.

 

[TexasRedneck]

I've mounted 4 - but I was present when they poured the slab, so I know where the cables are. You might also try a metal detector - it should work well.

 

[ZX9RCAM]

People who delivered my safe just drilled holes when it was located where I wanted it, lol.

 

[Vaquero]

You'll ruin a masonry bit before you do much damage to a post tension cable.
Proceed.
Yes. I have owned a home built on a post tension slab. I actually got to watch the slab being poured. And most of the post tension pulls being done. Your drill is insignificant.

 

[F350-6]

... You might also try a metal detector - it should work well.

There's also rebar (or at least should be) in the post tension slab. That can add to confusion if the metal detector isn't sensitive enough.

 

[Charlie]

I was in the concrete business many years. Post tensioned slabs are good to go as well as standard rebar. I would have no concerns.

 

[dartsinsa]

I poured a small foundation (about 4 inches high, just bigger than the safe) when putting into a basement once. Figured it would add some protection against water. Then drilled into it to lock down the safe.
Just an idea, not sure if it makes any sense on a slab, but was good in a basement.

 

[Charlie]

Slabs are slabs! Basement or building floors. If it's not where a beam is (doesn't really matter), use 3" locktight bolts. Four inch, etc. doesn't really get you any better if someone is pulling them out they can either do it or not. Of course don't use 5" locktights on a 4" slab.

 

[Dawico]

To be 100% sure, x-ray the concrete. That's what they (professionals) do before the cut it.

Looking to save money? You can try looking at the edge of your foundation, measuring where the straps are, measuring the inside, and double checking with one of those magnetic stud finders, but there is other steel in the concrete too.

If you have access to thermal imaging, you might be able to warm the concrete for an extended period so the steel strap gets warm too, then throw a bag of ice on the concrete for a bit so it cools quicker than the steel and figure the location that way.

I've mounted 4 - but I was present when they poured the slab, so I know where the cables are. You might also try a metal detector - it should work well.

Nope and nope. All worthless. The X-ray we had was anyways. Professional company did it and the marks weren't accurate at all. Drilled in "clear" areas and still hit them.

Built a restaurant that was a post tension slab. I had to drill 100 or so 5/8" anchor bolts plus 20 bigger HD bolts including drilling 1 1/8" holes 30" deep. All deeper than the cables.

Like Vaq said the cables are tough. If you are drilling and hit something then stop and move or go at an angle. You aren't going to pop them just by hitting them. Keep drilling into them and maybe but you'd really have to try.

 

[Charlie]

Nope and nope. All worthless. The X-ray we had was anyways. Professional company did it and the marks weren't accurate at all. Drilled in "clear" areas and still hit them.

Built a restaurant that was a post tension slab. I had to drill 100 or so 5/8" anchor bolts plus 20 bigger HD bolts including drilling 1 1/8" holes 30" deep. All deeper than the cables.

Like Vaq said the cables are tough. If you are drilling and hit something then stop and move or go at an angle. You aren't going to pop them just by hitting them. Keep drilling into them and maybe but you'd really have to try.

Exactly true! And keep in mind, most 4" slabs in residential construction are really 3 1/2".

 

[avvidclif]

A 13 oz tube of silicone sealer, spread around on the slab and put the safe on it. Just don't plan on moving it after it's set up.

 

[Dawico]

Slabs are slabs! Basement or building floors. If it's not where a beam is (doesn't really matter), use 3" locktight bolts. Four inch, etc. doesn't really get you any better if someone is pulling them out they can either do it or not. Of course don't use 5" locktights on a 4" slab.

Anything less than epoxy is for chumps.

A Titen will do in a pinch though.

 

[Dawico]

A 13 oz tube of silicone sealer, spread around on the slab and put the safe on it. Just don't plan on moving it after it's set up.

First off, get good Silicone.

Secondly, make circles with it. The suction cup effect has amazing strength.

 

[jjkukla]

One of them rare earth magnets may also be able to detect steel in the slab, if you're that concerned. I think some higher end stud finders will even locate rebar. But, as others have said, I'd drill til you hit something then adjust. Good luck.

 

[TxStetson]

A 13 oz tube of silicone sealer, spread around on the slab and put the safe on it. Just don't plan on moving it after it's set up.

First off, get good Silicone.

Secondly, make circles with it. The suction cup effect has amazing strength.

This right here. Just make sure it’s exactly where you want it, because it ain’t moving afterwards.

 

[SQLGeek]

I've considered that route. My problem is that I don't know if we will be in this house long term or not.

Sounds like drilling will be safe enough, I really just don't want to bugger up the cables.

Appreciate the advice folks.

 

[avvidclif]

Dupe

 

[oldag]

My loaded safe weighs enough that it is not going to be moved unless someone opens it and takes things out.

Put some lead or thick steel plate in the bottom if you think someone could move the loaded safe. Pretty easy to make it heavy enough they won't be able to cart it off.

They can always cut their way in, of course.

 

[ZX9RCAM]

One reason for bolting down a safe is to make it more difficult to tump over and cut on.
It's not necessarily about moving it.