Locating Rebar in Concrete

Is there a simple way to locate rebar in existing concrete? I need to drill a few holes in a concrete slab (basement), and the last time I did that, I kept hitting rebar. I know you can buy some equipment for doing this, but I was hoping that maybe I could rig something up with a simple magnet-- kind of a beefed up stud finder.

Do you have access to a stud detector? They work great for finding the rebar in existing concrete. The cheap ones are almost worthless for actual stud location, but are fab at finding rebar.

I never had any luck with a magnet. YMMV, but I need the beep and the blink.

Yeah, I have a stud finder. I’ll dig it out of the toolbox and try it. I was assuming it was too weak a magnet to react to something that might be an inch or more away.

There are stud finders that have a little magnet pivoting in a small plastic case, and there are stud finders that measure their capacitance against a surface, and maybe other kinds. Which kinds are people talking about?

I think a magnet hung from the ceiling on a long thread, so it almost touches the floor, would do well. But I haven’t tried.

Quick way to find rebar in concrete: hand me a hammer drill as ask me to drill a hole anywhere in a slab of concrete.

Pretty much how I do it.

Hell, that’s how I do it, even when I have the pour plans right in front of me. Damn as-builts! Thank god for thermite rods.

Thermite rods? Do tell.

The first one.

I’ve poured a lot of residential foundations, and I can tell you where the rods are in them. Two runs of 4-bar, sitting next to each other on the second row of ties from the top, twist tied every so often. You all must live in place with Building Inspectors or something…

Well, they’re not technically thermite, but that’s what we called them (the actual name is thermal lance. They do use iron and aluminum (as well as magnesium), though. They’re basically a steel tube with an aluminum rod inside*; one end is hooked up to oxygen, which is forced through the annulus, and the other end is ignited. They burn bright; even brighter than regular termite, because the combustion takes place in a basically 100% oxygen rich environment.

*Wiki describes their makeup as an iron tube with iron rods, I don’t know if we used a slightly different type or if I’m remembering incorrectly. I’ll tell you one thing I remember for sure, though: watching a Mk-84 go through a concrete wall at Mach 1 is a lot more fun than drilling the holes to attaching the slab to its supports. The cleanup sucks, too.

Well I came across this forum looking for simple ways of finding rebar studs in ceilings, f.x. using a magnet or other means, but found none.
So I start writing my friend to see if he can locate a stud finder somewhere. Suggesting he might have a MacGyver solution it all of a sudden struck me to construct a studfinder using a strong magnet on a raft in a transparent bowl of water, alike an oldschool compas, and I did. It works excellent! I measured the studs to be about 25cm apart following the behavior of the magnet, which moves about freely in the bowl of water with ease. Only thing it doesn’t measure is the depth of the beam.
Anyway. I know this thread is four years and older, but thought I needed to share in case others stumble upon the same dilemma and decides to google it:-)


Thanks MacGyver for divine inspiration in a time of need :slight_smile: