I have boulder stone foundation and would like to drill a hole through it for a gas line. How can I do this?

The rocks in the foundation tend to be about 12 to 20 inches and diameter and they are mortared together.

  • 1
    It depends on the type of rock. I would suggest putting the hole on a mortar joint. Going through some rocks is a PITA and also can lead to it cracking no matter how careful you are.
    – DMoore
    Commented Jun 27, 2016 at 21:24
  • 1
    See if the gas company will allow the line to exit the ground outside the foundation. They can install the meter outside and run the line into the house through the sill.
    – mikes
    Commented Jun 27, 2016 at 21:31
  • I do not want to cut through the sill. The type of rock is hard, hard rock. Commented Jun 27, 2016 at 21:38

1 Answer 1


Diamond hole saws work well for this with water. If this is anything like the stone foundations I have worked with there will never be a straight mortar line that could be used. On one of the first walls I drilled through I used a hammer drill and bit , The hammer drill caused the rock to break out on the back side and it was very tough to repair. This is the type of drill. once I get about an inch in I chip out the center and go deeper repeating the chipping process as I get close to the bottom of the saw. A really Good quality one may make it depending on the rock type. Don't go cheap or you will spend more time getting new ones and even though they are close to the same size sometimes you ending up having a slightly larger bit the second time (also found this out the hard way)

  • 1
    I've dealt with blowout from penetrations through concrete and smaller rock walls (<6") and as it's normal to caulk the penetration once finished the blowout is covered. You're saying an SDS on this size stone would cause significant blowout?
    – Chris
    Commented Jun 27, 2016 at 23:02
  • I was only drilling 1-1/4 or 1-1/2 hole and about 10" out of the back blew out. it was a historic home and this was about 1' above the floors (sitting room). It had be repaired to the "groups approval" and re polished the inside wall had been polished in the late 17 hundreds.
    – Ed Beal
    Commented Jun 27, 2016 at 23:14
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    The easiest solution is to call a company that does this all the time and have them core drill it for you. I had a drilling company do 6 holes through my 10" foundation walls for $250. You can buy core drill bits for hammer drills but unless you already have the drill, the drill and bit will cost you $400 or more.
    – ArchonOSX
    Commented Jun 27, 2016 at 23:27
  • 1
    Yeah, you'd need like $1k worth of stuff. A 1/2" bit for the pilot hole (so you can do both sides and not have any blowout) and then an appropriately sized diamond coring bit, and one badass (corded!) hammer drill. - Wait, how do you use those bits if they don't have a centering drill bit?
    – Mazura
    Commented Jul 30, 2016 at 18:26

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