I need to enlarge a few holes from 40mm to 50mm in a cinder block wall and in a concrete beam.

Chiseling will do much damage and need patching, can I rasp it with a wood rasp?

  • Why not just drill a larger hole with a 50mm bit?
    – Steven
    Aug 14 '15 at 15:28

The metal on a wood rasp would be way to soft to make any type of dent in the concrete. The only thing you will do is destroy the rasp.

You should use a roto hammer with the proper sized bit to widen the hole.


Yes, you can and it will work. It will also dull your rasp.


You could use a heavy duty drill and a diamond encrusted bit, such as this one

diamond bit

They can be found on-line and in some big box stores for about $20.

When grinding or cutting very hard materials like concrete, you should use a lubricant to reduce heat. Usually a small constant drip of water at the cut point helps.

 Images and links for illustration only, not an endorsement of goods or sources.

This is the correct tool for rasping concrete but it won't fit in a 2" hole. I suppose you could ruin a file (and the better part of a day) to get it done; CMU's aren't that hard.

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I'm adding my own answer since I tried to use the rasp.

It didn't work. The rasp can ease hard corners on cinder block and even a little bit on concrete, but it won't bite enough to enlarge a hole.

The method I use was a hammer drill with a chisel bit. I hold the chisel against where I want the edge to be and pressed the trigger very slowly. I did this so that it dig about 1 cm inside the concrete, then I move to the side and did that again making a contour. After that I used more force to break inside the contour. That way I could make a pretty good edge that requires minimum patching.

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