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Keep breaking bits when you're trying to drill through concrete?

I broke two bits drilling holes in my garage floor with a rented hammer drill. What did I do wrong? David D., Boise, Idaho

The most obvious possibility is that you hit a piece of rebar, or reinforcing steel. Or maybe you found a cast-iron drainpipe. If you see a pipe exiting the floor at any point, assume that that's what you're hitting and drill elsewhere.

You might think that a bit strong enough to drill through concrete could also handle steel, but a masonry bit's tip and flute geometry are completely different—thicker and blunter, meant to pulverize. Also, the hammer drill was probably in percussion mode, which simultaneously pounds and drills through concrete, stone, or asphalt. That percussive action broke the bit when you hit steel. Even if you'd switched to rotary mode, it wouldn't have helped. The bit may not have broken, but it wouldn't have made any real progress through the steel.

First, determine whether you can move the hole to another location or drill a shallower hole. If neither is practical, switch to the next heavier rental drill, called a rotary hammer. Get a masonry bit and a rebar-cutting bit. When you hit steel, back out the masonry bit and install the rebar cutter. Switch the drill off hammer mode and into drilling mode, and drill through the rebar before backing the bit out and switching back to the masonry bit and hammer mode.

The other issue I didn't mention is age. Not yours—the concrete's. Concrete hardens as it ages. Take your time and let the drill do the work with as little muscle as possible on your part.

This story appears in the February 2017 Popular Mechanics.

Roy Berendsohn has worked for more than 25 years at Popular Mechanics, where he has written on carpentry, masonry, painting, plumbing, electrical, woodworking, blacksmithing, welding, lawn care, chainsaw use, and outdoor power equipment. When he’s not working on his own house, he volunteers with Sovereign Grace Church doing home repair for families in rural, suburban and urban locations throughout central and southern New Jersey.

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