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Post tension slab drilling

Discussion in 'Garage / Workshop' started by DWreck, Jul 5, 2013.

  1. Jul 5, 2013 at 8:58 PM
    #1
    DWreck

    DWreck [OP] Famous Fabrication Vendor

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    I'd like to use some drop-in anchors in my post tension slab garage for mounting miscellaneous tools on a post. I understand that cutting any of the cable can cause extensive damage and I am worried about doing it. Has anyone done this successfully, unsuccessfully? Process used?

    Ready, set, GO!
     
  2. Jul 5, 2013 at 10:22 PM
    #2
    Rich91710

    Rich91710 Well-Known Member

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    Unless you know EXACTLY where the cables are, don't.

    Hitting a cable will not only result in damage, it can kill you.
     
  3. Jul 5, 2013 at 10:30 PM
    #3
    DWreck

    DWreck [OP] Famous Fabrication Vendor

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    Have you seen this in person or is it a story your friend told you happened to his sisters boyfriends uncles friends cousin?

    I'm only saying...:rofl:
     
  4. Jul 5, 2013 at 10:40 PM
    #4
    Rich91710

    Rich91710 Well-Known Member

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    Comes from guys in the industry.
     
  5. Jul 5, 2013 at 10:42 PM
    #5
    DWreck

    DWreck [OP] Famous Fabrication Vendor

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    Okay. Not trying to be rude, just looking for reliable info. I too have been in commercial construction for 9 years but know nothing of post tension slabs.
     
  6. Jul 5, 2013 at 11:05 PM
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    DoorDing

    DoorDing Someone was there .

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  7. Jul 5, 2013 at 11:15 PM
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    DWreck

    DWreck [OP] Famous Fabrication Vendor

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  8. Jul 5, 2013 at 11:22 PM
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    acdronin

    acdronin Well-Known Member

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    Just talked to a buddy of mine who told me about breaking one of those, nasty expensive fix, don't fuck it up.
     
  9. Jul 5, 2013 at 11:23 PM
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    acdronin

    acdronin Well-Known Member

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    Oh yeah, he said he thought it was rebar, it has a sheath that makes it hard to tell what it is.
     
  10. Jul 5, 2013 at 11:38 PM
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    DWreck

    DWreck [OP] Famous Fabrication Vendor

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    I had a pex waterline above the concrete that I noticed when chipping up tile in kitchen. Home warranty was called and came out to bury it further. The guy went at my slab with a jackhammer like a bull. He hit and exposed the PT cable and began to chip around it. He went all the way to dirt and refilled the hole.

    What I'm getting at is I saw how hard he hit the cable with a spade on a jackhammer and don't quite believe that a 1/2" drill bit could damage it if I go easy.

    Still weary though.
     
  11. Jul 5, 2013 at 11:41 PM
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    acdronin

    acdronin Well-Known Member

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    If you break it, you'll know in a hurry. Good that you didn't, sounds like a successful job.
     
  12. Jul 5, 2013 at 11:45 PM
    #12
    DWreck

    DWreck [OP] Famous Fabrication Vendor

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    Minus the curing left a discrete crack on the surface where he filled. Luckily we went with a troweled concrete stained finish and it blends lovely!
     
  13. Jul 5, 2013 at 11:46 PM
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    llibrm

    llibrm Well-Known Member

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    How fresh is the slab?
    How thick is the slab?
    What size drop-ins do you plan to use?


    After 15 years of industrial electrical work, I've set more than a few drop-ins in post tension slaps. Unless your going to be setting anchors over 5/8" ( bolt size, not OD of the anchor) you have nothing to worry about. Now that being said, you still need to take precautions, but post tension slabs are usually 10"+ thick. The cable is going to be in the centre of the slab.

    If you are still horribly paranoid, you can always have the slab x-rayed.

    Over kill never fails, but check your anchor ratings first. You might not need that large of an anchor.
     
  14. Jul 5, 2013 at 11:46 PM
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    acdronin

    acdronin Well-Known Member

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    nice!

    Spent the day painting trim, not my gig but a bunch of handyman stuff came my way, it's ok I guess, change of pace.
     
  15. Jul 5, 2013 at 11:48 PM
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    DoorDing

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    I haven't checked the latest models, but some of the studfinder type tools may be able to detect cables, rebar, or conduit in concrete. Worth a look.
     
  16. Jul 5, 2013 at 11:50 PM
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    acdronin

    acdronin Well-Known Member

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    If i could get a current onto one end I could take a 521 Locator or a Dynatel and I'll tell you exactly where it is and how deep too.
     
  17. Jul 14, 2013 at 1:57 PM
    #17
    rogerkamp8817

    rogerkamp8817 Well-Known Member

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    if you are really interested in finding out where those cables or rebars are, one way to find them is to perform Ground Penetrating Radar (GPR) testing. it will send radar to the ground and the signal will reflect back and show where the metal is.

    this will probably cost at least a grand though. lots of places won't test residential houses either due to liability reasons.
     
  18. Jul 14, 2013 at 2:06 PM
    #18
    DWreck

    DWreck [OP] Famous Fabrication Vendor

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    I ended up drilling the sidewalk leading to my door. Right behind a big ash tree so I'm still working in shade!
     
  19. Aug 23, 2013 at 12:51 PM
    #19
    fccc2006

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    If your garage has two exposed sides (front or back and one side) that have dirt or planter you can dig down and locate the stop plate that the cable goes through.
    This plate may have been covered over with cement patch, if so you will be able to spot the patch because it will look different that the surrounding concrete. You might have to hose off the footing to get rid of the dirt so you can pick out the patch easier.
    Once you find one then locate a 2nd one about 24 inches away. Then do the same around the corner to the other side.
    Take measurements from the cable locations to the footing corner between the two sides. Go inside your garage and plot the measurements on your floor. Remember to adjust your measurements for the thickness of the walls and wall coverings (drywall or shear wall covering).
    This will give you a grid for your cables and you will know where you can drill.
     
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