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Drilling test holes for depth confirmation
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04-09-2013, 04:15 AM #1
hausenheimer Newbie *
Status: Offline Posts:9 Threads:1 Joined:Mar 2013
How close to a test probe location do you guys drill a "test hole" to see how deep the slab is?

I am on a job in North Carolina. I drilled (3) 3/8" and used a hanger with a hook shape at the end to find the depth of the slab. I found 6", 6.5" and close to 7". I was willing to assume that the tests needed to be based on 6.5". It was a 5 probe job, when I got around to the front of the store, I figured I should do one more depth test between my probe hole and the edge of the slab, just in case. I was about 7' from the exterior wall. I found that the slab was only 4" deep here. Huh

This was all weird to me because these chain store that I test most often, are almost ALWAYS 5". Also, now I am questioning all of my probe depths, except for #5 becasue the depth test was within a couple feet of the probe hole. I have always made it a point to not do my depth test near my probe holes, because I was afraid the compromise in the moisture barrier would affect the test. I do fill the holes with epoxy when I am done. Should I go back and drill depth holes near all of my probes, just to be sure? If so, how close can/should I be to my probe holes with my depth tests?

04-10-2013, 06:08 AM #2
Rubensgt40 Concrete Moisture Coach ***
Status: Offline Posts:172 Threads:13 Joined:Oct 2011
I wish I knew how to answer that.

Same discussion brought up on this here thread

Although it did get a little off-track (for once not my fault JD Smile )

I don't think that the proximity of a narrow test hole to the probe location will be a big deal - but I have no scientific evidence to back that.

That said, I just did a test in a school where I hit re-bar three times before I finally got a successful probe hole. I will patch the dud holes up with some portland cement mix, but obviously not until after the readings are taken. I'm a little paranoid that the water in the patching mix will show up somewhere nearby...again, probably nothing scientific to back that but you can't be too careful.

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