Anchoring safe to floor, and ....oops?


March 24, 2010, 11:08 PM
Do I have a problem here?

I was drilling holes through my home's foundation to secure two safes. A standard masonary drill on a regular electric hand drill went right through the foundation...ALL the way through.

In each case, I hit a void after about five inches. Is this a problem?

I'm wondering if capillary action will now draw water up through the holes and into the safe interiors or into the house.

I once had a dog that peed all over the garage in a different house. Her urine apparently reacted with the concrete, making it somewhat porous. Whenever it rained, massive puddles of water would seep up wherever she had screwed up the concrete. (FWIW: I got rid of the dog when it ate a door.)

Will I now have a similar problem with these holes? Should I pull the bolts and fill them with epoxy or something?

If it matters, I live in Florida. It rains in Florida. Sometimes, it rains a lot.

- - - Yoda


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March 24, 2010, 11:29 PM
I want to hear more about the door eating dog...
As for the holes, if I were you, I'd call a building contractor and ask them. You have lots of holes in your foundation for piping and such, with no current problems, correct? Find out what they used to seal those opening with, maybe?

Edit to add, I have NO housebuilding or concrete experiance.

March 24, 2010, 11:30 PM

sometimes there are voids under a slab too many is not good

March 24, 2010, 11:54 PM
your foundation may not be more then 5 "s thick. i did the same thing at my commercial building and thought something was amiss. but upon asking some concrete guys its normal

March 25, 2010, 01:44 AM
Not trying to preach or anything. I hope you let me help you out.

You did not drill into the foundation. You only drilled through the floor slab. The typical residential concrete slab-on-grade is only about 4" thick, maybe 5" sometimes.

The building does have a foundation, but the entire floor is not a foundation. The foundation is located beneath building elements that carry the building's major gravity loads or lateral loads. A slab on grade is not one of those elements. Typical foundations for single family homes are continuous footings made of reinforced concrete, but may also be piers, piles, grade beams, manufactured masonry, stone masonry, or pad footings. They tend to be a foot thick or more, often 12" to 24" depending upon the soil and the building load. So you didn't drill into any of those.

Most floor slabs (especially Florida!) have a vapor barrier under the concrete. If you drill through the membrane, you expose the concrete to water damage from below. My suspicion is that it's too late, you already done screwed up. To fully protect from water damage takes more than a Hilti adhesive. It will require repair to the vapor barrier, which requires removal of the floor slab for access to the barrier membrane. But I doubt if you will do that. Most likely, you will fill the hole with any handy cementitious material you have nearby. I guess that's better than nothing.

1/2" diameter expansion anchors will work for your safe, and generally require only about 3" embed. In many cases, lead anchors will work just as well, about 1" embed depth.

March 25, 2010, 07:03 AM
Ants is pretty much spot-on. You didn't drill through the foundation, just the slab. Your bit ran through the solid concrete and down into the gravel bed beneath.

If you do live in a very wet place, you could indeed get some water infiltration. I'd be hesitant to say a couple of small holes in the moisture barrier are going to do much damage -- especially as the moisture barrier itself is generally just a few sheets of plastic laid out with overlapping seams before the concrete is poured, but anything is possible.

I'd get some hydraulic cement mix (like these:, follow the instructions to mix it, and then pack as much as you can down into the holes. It will expand a bit as it cures to seal the holes up.

You could use the bolts to tamp the last of the mix in and then lock the anchors before it cures. Should make for a solid installation. When it does cure, I'd add some silicone caulk around the bolt to seal the hole before you bolt the safe down.

Then check for moisture every once in a while. (Which you should do anyway.)

March 25, 2010, 08:40 AM
Fill the bottom 1"-1 1/2" of the hole with some concrete epoxy. Then, when it's starting to get firm, put in more epoxy and drop in a stainless steel anchor stud. Then, tighten it. You should be able to inject more epoxy around the stud (into the hole) after it's installed and tight, to seal and fill the hole completely. Then, lower your safe down and bolt it tight. If there's any space between the safe and the floor where the studs are, it'd be best to put a spacer in there. That way you won't be pulling up on the slab when you torque down the safe.

I recommend using studs rather than bolts because they're easier to mess with (no safe on top) and because they'll be tight and set when you torque down the nut inside the safe; you won't stress out the hole as much.

March 25, 2010, 04:51 PM
Just how long of a bolt were you going to use? 2 1/2 - 3 inches would have been more than enough

March 25, 2010, 06:11 PM
What ants and Sam said. Keep rolling forward and use something in those holes. You'll be fine.

Please post pics of the eaten door and the dead dog.:neener:

March 25, 2010, 07:13 PM
Fill them holes with a good silicon sealer, Like a GE II. Pack it in the holes good I mean shove it down with a wood dowel to get it to that vapor barrier. it will seal up the hole you put in the plastic vapor barrier. let that dry over night than put in your 1/2-13 anchor bolts. Hope this helps.

March 25, 2010, 07:15 PM
Fill them holes with a good silicon sealer, Like a GE II. Pack it in the holes good I mean shove it down with a wood dowel to get it to that vapor barrier. it will seal up the hole you put in the plastic vapor barrier. let that dry over night than put in your 1/2-13 anchor bolts. Hope this helps.

March 25, 2010, 07:26 PM
Expanding foam would fill the voids below the slab. I would use the harder, low expantion stuff.

March 25, 2010, 07:28 PM
going along in the same theme as has been mentioned already, but with my own little spin (and i am a general contractor)- i'd just fill with two-part anchoring epoxy (follow the instructions and brush/blow out the holes), reposition the safe, and drive all-thread down in there (cut to length first). let cure for however long your epoxy says to (usually 24-48 hours) and bolt down and stake. done. the epoxy will likely plug up the holes in the seal well enough. you might get a very small amount of moisure seepage into the slab, but you probably already have TONS anyway.

dont sweat it. we drill through foundations and slabs all the time, and almost always go all the way through just for GP. the epoxy seals all.

March 25, 2010, 07:36 PM
if it were me id take good silicone caulk blow the dust out of the holes an just pump some in then set anchors before it dries. There are special two part epoxies that also work good. There are always some small holes in the plastic anyway in my experience when the concrete is poured depending on the type of gravel the weight of it pops some rocks through. I have even torn out concrete and seen the gravel underneath stuck to the slab where it poked through the plastic and hardened into the slab

March 25, 2010, 07:45 PM
in fact, we just drilled an un-told number of holes straight through a slab not too long ago. the slab was 4" deep, and the plans called for the whole 4" worth of all-thread to anchor the walls to. everywhere a wall went, we drilled completely through every 12", cleaned out, filled with epoxy, and stuffed full of all-thread. and rather than have to do a lot (Edit--Sam)of cutting later, we beat the pre-cut 12" bars down into the fill below, till just enough thread to get a nut to bite was sticking through.

i suppose some areas might seal a concrete slab, but if so, it's only been in the last umpteen years. if your house is average house age of 35+, then there's no seal under there anyway, nor does it need any.

March 25, 2010, 08:23 PM
First, silicone caulk will not hold an anchor bolt. It takes a 2 part epoxy to do that.

Second, the easiest way to bolt down a safe is to use "Redhead" wedge anchors. It will never be able to be pulled up. But if you decide later to move the safe, after unbolting and moving the safe, all it takes is knocking the bolts down into the concrete to restore the flush floor. (Kind of like the toy Chinese hand (finger) cuffs. They go in, but don't come out.)

Third, as far as your worry about moisture. Get a tube of "hydralic cement", and squirt that into the bottoms of the holes. This stuff is used to fill holes in foundation walls (plumbing/sewer/etc.) to keep WATER (not moisture) out.


BTW- for the typical termit treatment, they drill all the way through to the soil under the slab. It's really no big deal at all.

Shopping A Round
March 25, 2010, 09:27 PM
What gun did you shoot the dog with?

March 25, 2010, 10:19 PM
Never use silicone for that purpose. Use 3M 5200. It is an adhesive and it is TOUGH.

Mt Shooter
March 25, 2010, 10:37 PM
Wow so many choices so many options....what to do what to do....

March 25, 2010, 11:56 PM

DO not go near any submarines.. ;)



Ps.. I never believed in ghost, (until now), but I think the dogs ghost came back to haunt you, and show you, (bite me, I'm back), by re-wetting the same exact spots in the garage floor after she tried to eat her way out of that garage and house.. RUFF!!!

March 26, 2010, 01:37 AM
You're screwed now, Yoda. Time to move, it is.

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