Determine Slab Thickness

[CC Solutions]

As you push with a hammer drill you sometimes feel the concrete break away at the bottom of the hole, it goes from solid to flexible, and I suppose he may know when he is close by feeling that break point. But I can't do it, I mean I'm drilling with a hammer drill not a smooth instrument.

I drill straight through with a 1/4" or 3/8" bit, fish the bottom with a wire bent on the end, and fill the hole with epoxy or polyurea.