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I drilling somewhat deep holes (inch and a half) into concrete and I'm hitting something hard in two out of my four holes. I'm fairly sure it's not metal I'm hitting and I'm wondering how to proceed. It's a new building (finished half a year ago - in October 2018) and it is in Sweden, so I'm sure modern building standards have been followed.

I'm using a proper rotary hammer and a proper concrete drill for the job and as far as I can tell the tip is not getting dull or anything. Could it be a rock or something? Or is modern concrete fairly uniform? Any suggestions on how to proceed and get past this obstruction?

  • If you could find a tiny rare earth magnet and glue that to the end of a rod, you'd learn if it was rebar you were hitting. If it's rebar, a normal drill bit won't do you any good. If, on the other hand, it's a stone, a new and very high quality drill bit will give you a fighting chance. – Aloysius Defenestrate Mar 31 at 16:02
  • amazon.com/Bosch-HCBG800-Granite-8-Piece-Hammer/dp/B0000TZYZC. These granite bits work fir me when a masonry bit is not able to get through aggregate – Kris Mar 31 at 16:39
  • What are you drilling? Floor? Ceiling? Load-bearing wall? How sure are you it's not metal, especially structural steel (rebar, tension rod or cable)? – TooTea Apr 2 at 9:07
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You may be hitting rebar, the reinforcing steel embedded in concrete. You can buy a rebar cutter the same size as your concrete drill bit to get through the rebar then switch back to your concrete bit once through. However a great deal of caution is in order.

It's pretty hard to determine whether you're hitting a very hard bit of aggregate or steel / metal, and if it is metal, it's hard determine whether it's safe to drill that metal. In some cases, for example concrete beams, cutting the steel in the concrete can weaken the beam. It's also possible you're hitting a water pipe, waste pipe, or an electrical conduit.

  • True, it could absolutely be rebar. I'm pretty sure it's not water or waste though, seeing as the bathroom is located in the same place on every floor in our building and nowhere near this wall. – Fylke Mar 31 at 12:35
  • What about a pressurized natural gas line? Can you rule that out? – Billy C. Mar 31 at 22:32
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You are probably hitting a stone - part of the aggregate used to make concrete...

If you are lucky your drill bit may cut through it...

If you are not then the bit may "drift" off and make a larger or angled hole giving you other problems...

A good quality masonry bit is a must...

When I have had this in the past re-locating the object by 1 or 2 centimeters has solved it...

  • Is there any other type of drill that might be better suited to get through the rock that I could use to "gain purchase" before going back to using the concrete drill? – Fylke Mar 31 at 10:45
  • Good masonry bits are usually sufficient - but the real issue I have found is how the bit is hitting the stone - if it is only on one side etc then it always drifts off... – Solar Mike Mar 31 at 10:47
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You're probably hitting a steel cable used for post tensioned concrete. You need to find out if you have that kind of floor system before doing anything more.

If you cut that cable you're looking at a crazy amount damage when that steel cable breaks and shoots out of the side of the building. The correct procedure in a post tensioned concrete floor is to have it x-rayed located to verify your holes are in places where there are no steel cables.

Basically you shouldn't drill through it, and so you need to find another place to put your hole.

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    It would indeed be crazy to cut a tendon, but it's hard to guess at the moment if OP is indeed drilling prestressed concrete. – TooTea Apr 2 at 9:13

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