I've drilled a fair number of holes through concrete, and the biggest
obstacle is reinforcing steel. If your house dates from 1920, you might
be able to find out what local practices were then, and if you're
lucky, there's probably no rebar.
You could line drill the hole with a 1/2 or 3/4 inch carbide bit, or
you may be able to rent a large rotohammer and a 4" carbide core bit.
If you can't rent the bit, you may be able to rent the tool and buy a
bit and the shank it screws onto. The carbide core bid doesn't need
water, so it's only mildly dusty instead of really sloppy.
After you find out what all this will cost, you can then compare it
with what it will cost to have a concrete-cutting contractor come in
and do it for you. If they cut with diamond, it may or may not need
water, but they're equipped to deal with it. The advantage of diamond
bits is that they can cut through steel, too.
The most cost-effective is to drill the outline with a series of small
holes, but this is also the most time-consuming.
- Bill Rabel
Anacortes, WA
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