Stone basement walls are typically 18" (or even more) thick. It has to
do with laying up the stone.

The early settlers in the Minnesota Iron range used to make basement
walls with hand mixed slip formed concrete. To save on expensive cement,
they filled the walls with local rock. As in mostly granite rocks 3" to
15" across. You could get a very solid rock wall with only about 25%
concrete mix. But drilling through this to put in utilities later was
something else!

Jon Elson wrote:
Proctologically Violated©® wrote:

Awl--

Somewhat related to my dust collection follies, I want to put another
vent in the garage proper, thru, you guessed it, an 18" foundation
wall. I don't have too many other choices, except mebbe venting down
the main sewer. Inyone done dat??

Drilling the hole--6" diam, I think--is doable, as I got rotary
hammers, a

18" thick??!!!!?? What? I can't believe your foundation is TRULY 18"
thick! The only structure I know of that thick is the cells at the
company in Amarillo that assembles nuclear weapons for the DOE. Well,
the Hoover dam is actually thicker than that, but I don't think your
house or garage is holding back 600 feet of water!

Can you fill us in on this?

I've punched a similar hole, for exactly the same purpose, through our
foundation/basement wall. We have the hardest concrete ever made, with
tons of Jasper in it.
My scheme is I made a giant punch tool out of a Macpherson strut
rod to fit my air chisel. I sharpen the thing on a bench grinder, and
just wail away at the wall. You get a huge explosion of dust, and the
punch makes progress at about 1/2" a minute. You make a few
penetrations nearby, then apply the punch at an angle, and a huge chunk
comes out. It took 2 days to get through the wall and open the hole up
to take the vent pipe. I have to resharpen the punch every 30 minutes
or so. There's no way you can really do this through 18". Even a core
drill machine will need a lot of setup work and extensions to properly
drill such a hole. A well-equipped driller will have the right gear
for this, but your average guy that drills a few holes for plumbing
and electrical access may not have the extensions.

Jon