Concrete walls in apartment buildings, how to avoid reinforcement when drilling?

[irrbloss]

Hi, I'm going to help my brother put up some shelves in a couple of concrete walls. He lives in a rental building built sometime in the 70s, I think. Is there any standard on how the reinforcement is placed? I assume they use some sort of reinforcement steel mesh? At what depth are these usually placed from the wall surface? I've got 30 mm plugs and plan to drill holes about 35-40 mm deep. Is it completely risk-free to avoid reinforcement at that depth? I assume a metal detector or stud finder wouldn't help much if it's some sort of reinforcement mesh? Is there a smart way to avoid hitting reinforcement when drilling into concrete walls in general? If you hit reinforcement, what do you do then? I assume a concrete drill doesn't do much good? Do you switch to a metal drill bit?

 

[oddan]

No problem drilling into reinforcement, get a concrete drill with 4 cutters and it will be as easy as pie.

 

[irrbloss]

No problem drilling into reinforcement, get a concrete drill with 4 cuts and it will be a piece of cake.

Do you turn off the hammer function then? I have a rotary hammer that takes SDS+ bits and bought a cheap concrete bit at Biltema, I think it only had two cuts.

 

[Lilllen]

My experience is that when drilling into rebar, there's a risk that the drill doesn't go straight in, but a little to the side. Then the drill tends to wander, and the hole can end up larger than intended. I've found that metal drills (hammer off) tend to wander a little less, but there's still a risk. It's usually best to start with a thin metal drill, and then increase the size. When it comes to plugs, I like those smooth colored (red) ones for 5.5mm drills, so you can then move up to brown 8mm instead, if the hole becomes too large. However, I don't drill into concrete very often, I should say.

 

[irrbloss]

Thanks for the response, then I know that it's not completely hopeless if one encounters rebar at least, but how is it with the depth where the rebar is located? Is it very shallow? When you measure up 3-4 cm between thumb and forefinger, it doesn't seem like much, but rebar might typically be relatively close to the wall surface?

 

[jonaserik]

Thanks for the reply, then I know it's not completely hopeless if you encounter reinforcement anyway, but how is it with the depth where the reinforcement is located? Does it lie very shallow? When you measure 3-4 cm between thumb and forefinger, it doesn't look like much, but maybe the reinforcement tends to be relatively close to the wall surface?

About 5 cm in is common with reinforcement, then if possible, if you hit reinforcement, you move the hole 3 centimeters diagonally in some direction, this is to avoid hitting iron in both directions and possibly a cross on them.

 

[irrbloss]

About 5 cm in is usual for reinforcement, then if possible, if you've hit the reinforcement, you move the hole 3 centimeters diagonally in some direction, to avoid hitting the iron in both directions and possibly a cross on them.

That was a good tip. Is there any standard measurement for the "squares" so that you can calculate where you shouldn't drill in the future? Like a CC measurement, but for reinforcement.

 

[jonaserik]

In walls that are cast for taller buildings, there is about 20 cm between vertical steel bars and about 30-40 cm between horizontal tie bars. If it's mesh reinforcement that is not normally used, it is certainly 200x200mm. But the thickness of the steel can also vary, hence the 3 cm diagonally.

 

[oddan]

Do you turn off the hammer function then? I have a rotary hammer that takes SDS+ bits and I bought a cheap concrete bit like that from Biltema, I think it only had two cutters.

I had the same problem in my previous apartment. Drilled (with a rotary hammer) into reinforcement and it just completely stopped. Read online that a new bit with 4 cutters would solve the problem. And it did, huge difference! Drilled with hammer the whole time.

 

[Rotekopp]

That was a good tip. Is there a standard measurement for the "squares" so one can calculate where not to drill in the future? Like a CC measurement, but for rebar.

Yes, there is a theoretical c/c measurement, but it's hardly something you can count on. There may be overlaps between reinforcement mats and repositioned iron due to form ties, electrical sockets, drainpipes, inserts, or if it's just so-called safety reinforcement, a 12mm every 40-100 cm. Stud finders usually have a setting for metal detection otherwise.