Securing a safe to a post-tensioned slab - DIY
If you have a post-tensioned slab, you cannot drill straight into it to bolt down your safe. I need to be clear that you should never, ever, ever, ever drill a PT slab on your own. You risk serious injury, death and structural compromise. No rational contractor will advise you to drill a PT slab without GPR or x-ray, and that costs much more than this project. However, you can still bolt it down using this simple do-it-yourself primer.
At each step, double check all your measurements, making sure that things are square, level and right. It is very hard to undo mistakes, so get it right the first time. First, how can I tell if I have a PT slab? LET ME BE CLEAR, If you are not sure that you have a PT slab, stop. Ask a professional before you drill. NEVER EVER DRILL A PT SLAB. I CANNOT STRESS THIS ENOUGH. Do not rely on your slab being stamped. Many are marked in the garage, and many are not. You can look at the outside of your slab if you are not sure. There will be grouted holes 3 to 4 inches in diameter every 3 feet or so. The best way to tell if you have a PT slab is to look for these holes, and look at a side where there is no concrete poured next to the foundation and the top 12in of the slab are visible. Do not rely on the slab being stamped as PT. If you think you might have a PT slab and don't want to ask a pro, then assume it is a PT slab. I took these photos for two reasons. One is to help you guys. Two, if I ever have questions on what is underneath this slab, I have proof I never drilled it. If I were you, I would document this project as a CYA. Step 1: Go to USPS and pick up a change of address packet. This has a coupon for 10% off your entire purchase at Lowe's. Home Depot will also take this coupon. You can save 10% on your safe and everything else, so buy everything you need in one swoop. The coupon used to be instant, but some now apparently require registration and take a few days to arrive via email. http://i41.photobucket.com/albums/e2...ps73bb781a.jpg Step 2: Plan your shopping list. Here are the things I used for this project: 2x6 for forms 2x4 to screed Sakrete Portland cement #4 rebar Wedge anchors 5/8 - 6in concrete edge and finishing tools Skilsaw w/ wood and masonry blades Sawzall w/ metal blade Drill w/ Phillips driver, 3/4 Metal bit, 5/8 Masonry bit Wheelbarrow Sika LatexR Concrete Adhesive Level Wedges to level Doobie blocks 3 in screws or concrete form nails Respirator Safety glasses Extension cord Then go to Home Depot (they have more of this stuff) or Lowe's and buy everything you need. Remember, you can buy your safe at the same time and get 10% off with the coupon. http://i41.photobucket.com/albums/e2...psbcef2022.jpg http://i41.photobucket.com/albums/e2...ps339da7b8.jpg Step 3: You'll want a diagram of the anchor hole dimensions of your safe if you are ordering it like me. I called AMSEC and the emailed me a diagram of their HS safes in a few minutes. If you buy it at HD, you can just measure it. You will want to sketch out the dimensions of your new housekeeping pad. I sketched mine out several times to get an idea of where I wanted it. My new safe is 40w by 26d. I made my slab 45x30 because those are great calibers, and because you want to be 4-6in larger than your safe. I"d go larger, but that would extend too far into my garage. Anyway, just sketch out what works for you. I went through a few different sketches before I figured out how large I could go and not be intruding on too much garage space. The bigger you can go, the better, but everything in life is a compromise. http://i41.photobucket.com/albums/e2...ps7631b5f4.jpg Step 4: Once you have your area sketched out, you need to scuff the slab. This will allow the new concrete to better adhere to the old stuff. Before you start, you NEED a respirator. This step will create a ton of concrete dust, so empty out the garage and cover what you can. Then, eyes, ears and respirator on. I used a masonry blade on my Skilsaw and a FatMax Fubar to do the job. I gouged the slab with the Fubar and dragged the masonry blade at a 45 degree setting across the concrete. Ideally you want to scuff the entire area of the slab, but I wound up going a few inches less than that. Remember, you just need to scuff the surface, not go deep. You can also use an angle grinder to scuff up the slab. Once the slab is scuffed up, make sure and get it cleaned off. Dust will severely weaken the bond, so get it as dust free as you can. http://i41.photobucket.com/albums/e2...psdaca5c14.jpg Step 5: Once you have the slab scuffed, you can set your forms. I won't go into how to do this as there is a ton of info out there on it, but just make sure that you have them level and secure. I secured mine to a workbench and then directly to the wall. A proper slab will not be perfectly level so that water drains out, so don't just set yours on the slab and go. You will need to level it out. http://i41.photobucket.com/albums/e2...pse836664e.jpg At each step, double check all your measurements. Just reminding you. :) Step 6: Now it is time to put in your rebar. This is where knowing the anchor hole locations is important. Put in the rebar on top of the doobie blocks so that you are certain to avoid the anchor hole locations. THIS IS CRITICAL. Once you are certain that the rebar is nowhere near where you are going to set your anchors, check your forms and your measurements again. http://i41.photobucket.com/albums/e2...ps81b3a4b5.jpg |
Step 7: Double check everything. Check that the forms are level and secure and that the rebar is not going to be in the way of the anchor holes.
http://i41.photobucket.com/albums/e2...psee159256.jpg Step 8: Now you are ready to mix and pour the concrete. The only special step you need to take here is to take the SikaDur LatexR Concrete Adhesive and make a slurry to put down. The directions are on the bottle. Then take the rest of the Sika and mix it in with your first batch of concrete. I mixed mine in a wheelbarrow. adding a 1/4 a bag of Portland Cement to each bag of Sakrete High Strength concrete. You don't want it to be too wet, and it needs to be well mixed. Then just dump it into the form. If you're not sure how to work and finish concrete, there are a ton of DIY primers online. Finish the slab, and once it is cured you can pull the forms. Now you've got a slab that you can bolt your safe down to. See the DIY sticky on how to bolt down a safe and go for it. http://i41.photobucket.com/albums/e2...ps301e7c78.jpg Step 9: Optional extra safe straps Once your safe is bolted down, it is probably not going anywhere. The weakest link in the chain is most likely the bottom of the safe, which will probably be ripped off before the bolts shear or the slab moves. To reinforce that, here is what I do. My last safe came with 10 gauge steel supports instead of a pallet. I take these, and drill two 3/4 in holes spaced correctly for my safe. Then I use these below the washers and nuts on the redheads to reinforce the bottom of the safe. On the left is what it looks like before, and on the right is after. Then I take a sawzall and cut the side off and cut it to length if needed. On a side note, this is the same steel used in most of those low-end Winchester/Canon/Browning/Cabelas/Stack-on/AMSEC safes. You'd be amazed how quickly a Sawzall can chop through them. On another DIY, I'll show you how to turn a $1000 safe into a much more secure container. http://i41.photobucket.com/albums/e2...psfb0d8f73.jpg Anyway, I hope that this helps. |
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I am making sure my safes are all secured to where they can't come out. I have a friend in our development (also with a PT slab) who had a safe, and it was broken into with a crowbar. Now her safe was crap, but even then they made the effort to pull it out and get it on its back. It was lagged into the plywood subflooring and came out easy. This housekeeping slab is the way to go if you want to take your safe with you if you move. I'm putting a very, very expensive safe here and don't want to leave it if I move. I'll be doing another DIY project with a much less expensive safe showing how to secure a safe to a PT slab if you really plan to keep it with the house. |
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Those cables are stressed to a degree that hitting them with a masonry bit won't cut them, but it will snap them. It isn't like hitting rebar. The tension in the cables makes them want to fly apart as soon as they are hit. More importantly, drilling a PT slab will void your home warranty, and if you hit a cable you're looking at a five figure repair bill. The risks of drilling a PT slab are enormous, and the effort it takes to solve the problem is a full day project at best with minimal cost. Seems like a no-brainer to me. |
drilling a two inch deep hole in any concrete is going to snap a tendon as often as airliners having a head on. Use epoxy to secure the anchors, not redheads.
Too much rebar, too many dobies (they create a void). Mesh pulled up to the middle of the pour would have been ten times better. But, a good training project for sure. |
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Only a moron drills a PT slab. |
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Yes, this slab is totally overbuilt if it were a driveway or a sidewalk or some other regular slab. However, the overbuilt part of it ran me about $4, and the extra strength in the slab makes that $4 well spent. |
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A 2in hole in a PT slab voids a home warranty for most people. That is very bad. Generally those tendons are 2in from the surface, but they don't always run parallel to the surface so you can absolutely hit one at less than 2in. That alone would be a reason to never drill a PT slab. Even if you were to drill a 2in hole and miss a tendon, a 2in epoxy anchor offers virtually no strength. A 2in hole with epoxy offers less than 1/8th the strength of a 6in hole, and the force requred to pull the anchors is less than the weight of a decent mid-level safe. A real contractor will get an x-ray or use GPR before they ever drill a PT slab. If you want to go ghetto, mess up your life DIY like you're suggesting, here is some factual info to digest. LET ME BE CLEAR, AS A LICENSED CONTRACTOR, ONLY A TOTAL MORON DRILLS THEIR OWN PT SLAB. NEVER EVER DRILL A PT SLAB. I CANNOT STRESS THIS ENOUGH. If you're still wanting to drill a PT slab, this is what a very stupid hypothetical contractor would do. I am not advising anyone to do this, because it is very stupid. Despite any reasonable professional advice to avoid it, he would look at the outside of your slab. There will be grouted holes 3 to 4 inches in diameter every 3 feet or so. The best way to tell if you have a PT slab is to look for these holes, and look at a side where there is no concrete poured next to the foundation. Do not rely on the slab being stamped as PT. He would guess where the cables run and drill, which is stupid. PT cables will be covered typically in a red plastic, so if he drilled it and hit plastic, he would stop what he is doing and then drive away, leaving you with a big problem. He probably had no idea that is the case, though, so when he hits the plastic, he keeps going until he snaps the cable. Then he realizes something is wrong, packs up his tools, and drives away hoping you don't have his information to track him down. That is why you don't do this yourself or hire very stupid contractors. The tendon anchors are under 10,000-30,000 pounds of stress in most residential slabs. If you hit a tendon, they fly apart like something under 30,000 pounds of stress, which is violentlly. The anchors can (and do) fly a few hundred feet and people have been killed by drilling PT slabs. Smart people don't drill them ever on their own, and professional contractors will not drill them without x-ray or GPR. If you don't mind ruining your foundation and killing yourself or someone else in pursuit of a 2in hole that offers no support, take paul0660's advice. Make it clear to your attorney that it was paul0660 offering that advice, and that I advised against it when you want to file your lawsuit. If you want to have a safe bolted to a PT slab, do what I said above which is to create your own housekeeping slab that you can drill and not worry about. Do not drill a PT slab. You can listen to a licensed contractor talking the talk and then walking it, or some internet certified keyboard expert. It is your house. Here is a nice video showing what happens when just one PT cable fails. |
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Thank you very much for this DIY! I have the PT slab and thought I was SOL as far as bolting it down. This looks like my next project. When you talked about a proper slab not being completely level you were talking about the existing floor, correct? So we need to take that into account when we make our new slab is what I got out of that. Just wanted to double check.
On a side note, I'm not home but I know the garage has the stamp but we also have an outside patio area which was there when we moved in. Would that usually be the same PT slab? I'll look for the holes when I get home but just curious. Thanks again for the great info! |
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All exterior residential concrete like driveways and patios that I've ever seen are just standard rebar. I would doubt that they are PT. I'm glad you found it helpful, that is what I was hoping for. |
I also want to note for post-tensioned slabs that if you drill into the slab - and avoid the tension cables, and yes void the warranty and such, if you later try to sell the house - you can get hit by prospective buyers on inspection with this. They can try to dock you on the asking price with the cost of fixing that. It is not going to help the sale, is what I mean to say. Of course, they might not be happy with the extra concrete work as noted here, but that is not a point against structural integrity.
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Also, when you drill for the anchors, make sure and drill a hole that is less than the depth of your new slab. Redheads sunk at 4in require something like 6,000-8,000 pounds of force to pull, so no need to drill the hole to China or into the PT slab. |
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If I had a lighter safe already here, your method would be the best by far to secure it down. |
I'm glad I read this- I called Boswell Safe about installing mine with bolt down service and they said they could drill down to 2 inches in my PTS. I'm going the slab route now, thanks!
UPDATE: see the finished pics on page 2 |
Cleaned up.
If anyone -really- wants a post back, none of them are GONE gone - I can bring one or two back. Generally ask a question, quote the question in the answer, allows the original question to be deleted. |
Thank you Librarian.
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good write up, thanks for the info
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this is great info. thank you
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And BTW, they'll still get in there if they have the time and tools for it. Bolting it only slows them down. |
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i have an inch gap in between the safe and the wall, do I fill the gap with a piece of wood then bolt it through to the stud? then wouldn't it void the warranty of the safe by drillingthe back side? anyway it's funny that people say that it's better to have a safe than not having a safe, now that I have a safe, I still have a problem |
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it is also important to note that you must READ and stamped noticed of PT concrete. In some cases it ONLY refers to the garage slab and not the house slab. You may be able to get information from the builder (based on age of structure). Check with your local building authority (city. county, etc) as they issued permits to the builder. As far as inspections of the concrete are concerned.......I have NEVER seen any inspector at each tract home inspecting concrete forms, placement, or finish work, including PT.
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Hi everyone,
I am new to the forum, but I just wanted to share my research on this subject. I also just purchased a new safe, and was wrestling with the issue of bolting it to a PTS. I contacted a VERY well known concrete fastener company, and purchased some 3 1/2" wedge anchors, I contacted them for guidance, and this is what they told me: "If you have any doubt do not do it. Most post tension applications maximum embedment is ¾”. In fact now that I know your application, I will not sell you any other anchor. If you want return the anchors you have and I will give you a full refund on the anchors" I thought that was rather severe, to refuse to sell me anchors (I guess we are in the era of big government/brother "watching out" for you!). But it made me think and research. I found that Red Head makes the RX38 (3/8") drop in anchors that only need a hole 3/4" deep, and are specifically designed for a PTS. I ordered some, and I think I will go with using the RX38s to anchor my safe. I know that ANY drilling is a risk, and I have to weigh out the risk of hitting a tendon. However, from several reliable sources I have determined that even IF I hit one, there is minimal chance I can sever or cut a tendon with a concrete carbide drill bit, using a hand held hammer drill. If I was using a rotary hammer drill, or actually cutting sections out of the slab...that would be another story. I am not trying to argue with anyone, just sharing a possible alternative. |
I was in a safe shop yesterday and the owner of the shop told me that you can just drill and that the cable is so tough that the drill will just go to one side of it since the drill won't be able to get through. And if this happens, just move the safe a little bit to move where the hole will be over and keep on drilling.
Then he quoted me $1300 for a 14 gun Amsec fire gunsafe. |
Pretty much that's what I've been told. I feel comfortable drilling 3/4"; HOWEVER, I have not dismissed the sticky idea of building the raised slab....My safe is one of those "inferior" $700 Winchesters, but it's MUCH BETTER than the Homak cabinet I was using before.
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SCOBUN,
Regarding the straps in step #9 of your sticky, where did you get them and do you have pictures of how exactly they go on the safe? |
Well, I am having more problems figuring out how/if I should bolt down the safe than when I was trying to decide WHICH safe to get! LOL!
I'm not sure I will build a raised slab in my closet, that might work great in the garage....but not in a closet. At the same time, I am having great doubts about drilling (even 3/4") into the slab....so I am leaning towards the 4x4s epoxied onto the floor and using lag bolts to secure the safe to the 4x4s I plan on getting a security system, so I just want to slow down the burglar. Odds are that IF my house is broken into, it will NOT be a pro, but rather a meth head that is just looking for quick "grab and run" items. So, I don't believe he would even mess with the safe, and if he did, he would do minimal damage to it and the police get there while he's trying to figure out which kitchen knife to use on the safe! |
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PT Slab Safe install
Excellent info. Thanks so much ;)
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Another option for a post tension slab
Redhead RX-38 drop-in anchors. Only need to drill 3/4" deep. You have a better chance of winning the lottery while getting struck by lighting then you do of hitting and severing a PT cable drilling a 1/2" diameter hole 3/4" deep with a masonry bit.
1,571lbs-1,987lbs of tension strength per anchor. Shear strength of 2,295lbs-2,903lbs per anchor. |
Great info! I need to find out if the slab in my new house is PT. Never would have thought anything about it and drilled away:facepalm:
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Great post and very timely! My house has PT slab flooring and I've been trying to figure out a cheap but effective way securing my safe in the garage.
Never thought it'd be that easy to add a pad on top of the slab! Thanks! |
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I've drilled thousands of drop in anchors, and suspended hundreds of pieces of HVAC equipment from those anchors. The key is you cannot drill two unless they are at least 10 times the diameter of the anchor apart.from each other. |
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