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Old 02-21-2008, 10:38 AM   #1
Marge
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Determining Post Tension Slab

Is there a way to determine if a slab is post tension? I know some have been done in AZ.
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Old 02-21-2008, 04:08 PM   #2
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Wow, not even a sarcastic comment around here.

Found a Post Tension Institute (no joke) and spoke with an engineer there. Explained a bit about how it works and how it's done in AZ. If a house here is built that way there should be a stamp in the garage concrete (near the overhead door) stating a post tension slab exists and one side of the exterior stem wall should show patches from the tightening of the cables. Neither item exists on the house so going to do some concrete demo.
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Old 02-21-2008, 05:03 PM   #3
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Ok, look here, Marge, this is whatcha do. Look 'round yer house for a big post. That's the Post part of this thing. On that there post ought to be a knob lookin' thing. If you turn that knob to the right it'll get tite. That's the Tension part. If it don't get tite, you ain't got no Post Tension slab now do ya? If you want more info on this subject and many others, Flat's gotta how-to manual for $19.95. Please send self addressed envelope...
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Old 02-21-2008, 05:28 PM   #4
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The plugs along the edge of the slab are the only way I know, short of chipping into the slab. Never heard of that mark onna garage floor, but never poured any of my own that way, neither.

I'd still recommend you be careful until you start findin' you some re-bar in there at least. Cutting one of those cables can be at least moderately dramatic.
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Old 02-21-2008, 06:06 PM   #5
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When I bought a new down down cx's way back in 2003, it had a post-tensioned slab. The concrete contractor came by with a cement mix and patched over alla holes...in fact he covered all sides of the slab with cement, so it looked better than the slab after it came outta the forms.

Cheers.
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Old 02-21-2008, 09:46 PM   #6
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Well heck Brad, I'll just find those knobs and Lefty Lucy all of them before I jackhammer.

I'm pretty confident we have a boring slab...boring is good.
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Old 02-21-2008, 09:52 PM   #7
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Oh, you've already purchased Jim's material.
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Old 02-21-2008, 10:01 PM   #8
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Told him the check is in the mail....
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Old 02-22-2008, 04:42 PM   #9
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Quote:
Originally Posted by Scott
The concrete contractor came by with a cement mix and patched over alla holes...in fact he covered all sides of the slab with cement, so it looked better than the slab after it came outta the forms.
"Plastering" the slab is just a normal step in foundation work down here, Scott. Pretty unusual to find one not plastered, in my experience.

But I don't know about them post-tension guys.

And I gotta admit I've never seen one of them "posts" up close enuff to figger out how the controls really worked.
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Old 02-22-2008, 06:33 PM   #10
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Don't really know nuttin about post tensioned slabs, but . . .

If there are cables going through the whole slab and spaced evenly could one use a metal detector to check for them?

I was able to use a metal detector to figure out where the wire was pulled up properly, where it wasn't and where it was left out of our driveway/sidewalk/patio job. I set it to give a strong signal where I knew the wire was pulled up properly. Then I would get a faint signal where it wasn't pulled up and nothing where the wire was left out. Didn't have to pay for the wire either.
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Old 02-22-2008, 06:40 PM   #11
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I stand to be corrected on this but I am of the opinion that although one needs to be cautious there isn't danger in doing concrete demo in a post tensioned slab. The danger is when one does saw cutting or coring...two activities that could cut through a cable. If the demo involved is chipping out some of the slab to move a drain line then as long as the cables aren't cut (which is unlikely with a chipping hammer) then one should be able to do that without a major amount of concern.

The only thing about using a metal detector would be that you couldn't determine if it's rebar or cable and I think both are used in a post tensioned slab.

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Old 02-22-2008, 11:17 PM   #12
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I don't remember the details, but an architect builder once described to me how they use "detectors" to find the cables and map out the slab before hacking away at the concrete. I got the distinct impression these things were not something to be dealt with lightly. We don't actually have one, so no firsthand experience.
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Old 02-22-2008, 11:24 PM   #13
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On commercial sites they use x-ray.
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Old 02-23-2008, 12:02 AM   #14
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We rented a chip hammer and will work carefully tomorrow. The engineer gave us three things to look for and none are evident. He did mention metal detectors but said rebar could skew the reading.

Maybe I should order the Schluter pan for tub remodels with the drain on the right......

We'll take it slow and easy.
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Old 02-23-2008, 04:05 PM   #15
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Happy to report all fingers, toes, eyes and appendages are still intact and functioning. Got everything hammered out and now the fun begins for Wiley. He wasn't too concerned until he saw the tub trap is under the wall and not in the bathroom. Bummer.
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