OT- Finding steel collars under concrete.
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  1. #1
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    Default OT- Finding steel collars under concrete.

    I recently finished pouring my deck in the back of the house. I tack welded 6" collars to the pans where service is to come up from underneath for an outdoor kitchen. I kind of screwed up and the collars were not quite tall enough. They are probably down about a half inch from the top surface. Tapping on the concrete has not helped me locate them. I know approximately where they are but not exactly. As you can see there is quite a bit of steel involved so not sure if a metal detector will work. Does anyone have a clever way of finding something like this?
    Attached Thumbnails Attached Thumbnails 3.jpg   2.jpg   1.jpg  

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    I'd try the metal detector. You sweep the coil back and forth to pinpoint the beep, so with lots of patience, you should be able to mark out enough points to interpolate circles in the right positions. Metal detectors can also be set for depth to penetrate, or you can raise the coil higher off the floor if you get too many nuisance responses.

    Even a stud finder might go deep enough.

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    When I did survey work we could take our metal detector and turn the sensitivity down to exclude things like concrete wire, smaller rebar, etc to find corners that had been poured over. The detector we used was for surveying, it only detected ferrous, was yellow, and had a 4x4 box on the end of a stick. I think they are still made, maybe you could rent one.

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    Use a pinpointer. Used by detectorists, it helps locate small objects after general location by search coil. $110 or about $16 if China made. I would find a detector guy and have them pinpoint it for you. Using the tip like a pencil it will sneak right up on the metal ring and give you good definition. Otherwise you'll be busting concrete and swearing.

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    Thanks for the tips guys. I never thought of turning the sensitivity down. Not a metal detector guy myself. My brother in law has one and I will try that. Thanks again.

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    I've learned that metal detecting is an art form.. Any idiot can find a man hole cover buried a foot down.
    They say it takes about 100 hours of use to "learn" a detector.. I'm not very good at it.

    Anyways.. Try posting over here, and see if you can get somebody local.. Some of those
    guys get a charge out of helping people out and doing something different than wandering
    around in the park looking for old dimes.

    http://www.treasurenet.com/forums/forum.php

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    Possibly a stupid Q and I'm not sure of your terminology, but as you've services coming up through the collars, can you not get to them from underneath? .......if it's a drain / sewer, often a good hard ram with a drain road will punch out a thin concrete covering.

    P.S. Some pics of the situation might help.

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    Maybe Its just me but I would have used a tape measure and a note pad before the concrete truck showed up.

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    Quote Originally Posted by crossthread View Post
    I recently finished pouring my deck in the back of the house. I tack welded 6" collars to the pans where service is to come up from underneath for an outdoor kitchen. I kind of screwed up and the collars were not quite tall enough. They are probably down about a half inch from the top surface. Tapping on the concrete has not helped me locate them. I know approximately where they are but not exactly. As you can see there is quite a bit of steel involved so not sure if a metal detector will work. Does anyone have a clever way of finding something like this?
    Ordinary cheap-arse "stud finder" should work just fine.

    Meant to be able detect a single nail or drywall screw, they easily find buried gas or water lines and re-bars in cast concrete where they are several inches back of the surface.

    "Map" the probable outlines of yer find. Drill within the center. Break 'crete 'til you hit a box wall. Worst-case, you patch some 'crete. BFD.

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    Quote Originally Posted by moonlight machine View Post
    Maybe Its just me but I would have used a tape measure and a note pad before the concrete truck showed up.
    They tried that....but Jimmy Hoffa is still MIA....

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    If they are steel and closer to the surface than the other steel, then I would try using a stack of those neo magnets. Just scan over the surface of the concrete with them and they will be attracted where the steel is. Here is a photo of me finding the studs behind a shower wall. The magnets actually stuck to the vertical wall and allowed me to hang plumb lines from them.





    I had about three or four of the magnets stacked together. I was only working over wall paper, but if your collars are only 1/2" deep while the other steel is a couple of inches below, you should be able to find them by the difference in the magnetic pull. And they are small so they will provide better resolution than many metal detectors. And they are a lot less expensive.

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    tack welds should show up on the underside of deck as discoloration or white zinc oxide powder

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    Can't help you with your question, but sure does look like a nice view.

    Bill

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    Quote Originally Posted by deltap View Post
    tack welds should show up on the underside of deck as discoloration or white zinc oxide powder
    "New" concrete still-yet, so right time of the day, a thermal imaging "gun" - or even condensed moisture pattern with the right lighting - might find those buried collar outlines rather accurately from topside.

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    I secound magnets, swing em just over the surface and they will find it if only 1/2" under, other way is metal detector, if that just finds rebar every were raise it up higher and sweep again, should only take a few goes to find it, all but the best metal detectors are really pretty shallow acting, especially in wet soil - wet concrete.

    Humble stud finder is anouther option, most of thoes have a pipe or wire function and work like weak ass metal detectors.

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    Might be able to locate them with a magnetic compass if you have one in your camping kit. The steel in close enough proximity to the compass should swing the needle.

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    As mentioned, a schonstedt metal detector, used by surveyors to locate buried ferrous metals would probably work. They can locate vertically oriented iron pipes very deep. Know any survey crew guys in your area?

    Dan L

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    My concrete contractor buried my tie-down anchors deeper than he was supposed to. The deepest ended up being 1 1/2" I knew the approximate location, but not close enough to punch the floor. I used the neodymium magnet trick. I just rolled a stack of 5 across the floor and watched the behavior. No problem finding the cap for the anchor.

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    Quote Originally Posted by crossthread View Post
    I recently finished pouring my deck in the back of the house. I tack welded 6" collars to the pans where service is to come up from underneath for an outdoor kitchen. I kind of screwed up and the collars were not quite tall enough. They are probably down about a half inch from the top surface. Tapping on the concrete has not helped me locate them. I know approximately where they are but not exactly. As you can see there is quite a bit of steel involved so not sure if a metal detector will work. Does anyone have a clever way of finding something like this?
    Hello Crossthread
    So if I read this right, your collars that you intended to use to run your utilities through the concrete slab, are not only buried 1/2" below the surface, but are also now full of concrete. So what good are they to you now??? Buy, borrow, rent, ... yourself a core drill & drill some holes through the slab.

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    I think it's time in this thread to bring out the "Diving rods"......

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