Wayne Whitney wrote:
Hello,

As part of a remodel project and reconfiguring an exterior wall, I
need to drill some 7/8" holes in my foundation to epoxy in 3/4"
threaded rod. So I got an SDS rotary hammer and an 18" long 7/8"
carbide hammer bit. I've never done this job before, so I'm looking
for some advice.

For example, how will I know if I hit a piece of the foundation rebar?
Hopefully this won't happen as long as I keep the new holes in line
with the existing anchor bolts. If I do hit a piece of rebar, is
there a way to drill through it? Most of my holes I could just move
over a bit, but two of them are tightly constrained and would be a
major design headache to move.

Thanks, Wayne




Wayne-

I done this a LOT, that is, drilling into concrete with rebar.

"For example, how will I know if I hit a piece of the foundation
rebar?"

The bit will stop advancing. With a good rotary hammer (Hilti,
Miluakee) the bit will make steady progress into the concrete. Don't
push hard on the tool, let it do the work.

You CAN drill by the rebar IF you only hit it "partially". If you hit
it dead on it will be nearly impossible to drill through with a rotary
hammer (unless it's only a #3 or 4 bar and you are very stubborn)

But do you reall want to sever the rebar?

Most epoxy anchoring goop allows for oversized holes, not a great idea
since it can lower the tensile valves if the hole is REALLY big but
much better (IMO) better than severing the rebar.

The worst thing that can happen is that you just barely nick the rebar
& the bit "corkscrew" passed it.

When you go the withdraw the bit, the drilling debris will cause the
bit sieze up in the hole.

A pair of vise-grips will be helpful but clearing the hole as you go by
withdrawing the bit often is the best bet. Even better blow & vac
it..

You'll get a feel for the rebar depth so you'll know when you in the
"danger zone".

Getting a bit stuck is a major PITA and can take a long time to futz
with to get out.

If you hit rebar with a bit I suggest that you stop, re-drill the hole
with a larger bit such that the smaller bit now can be "moved over" &
sneak passed the rebar.

SImpson & Sika both make good products for this sort of app; Sika works
in a regular caulking gun, Simpson needs a special one ($$'s)

Both products spec hole sizes; the SImpson website gives info about
oversized holes
http://www.simpsonanchors.com/catalo...guidelines.htm

SImpson reports no stenght reduction for holes up to 150% larger than
desired hole.
The SImpson website (& Sika for that matter) has a wealth of info

Long winded answer.........my bottom line, avoid severing the footing
rebar, work around it, over size the holes if need be & load them up
with goop.

Make sure you blow AND brush the hole.............the correct sequence
is brush, blow, brush (at a minimum) but ALWAYS end with "brush".

cheers
Bob