The longest drill bit I have is 23.62 inches and apparently the thickness of the concrete I need to penetrate is 27.5 inches. I don't wish to buy another drill bit, is there a smart solution?

The hole is for a gas pipe to go through, so the diameter of the bit is ~1.5 inches. I am drilling into the foundation, other side ends with a thin layer of plaster.

  • 27
    Do you have any longer bits of a smaller diameter that could be used to drill a pilot hole? If so, then you could locate and drill from both sides of the wall.
    – spuck
    Commented Jan 13, 2020 at 17:05
  • 1
    some hand drills can get the bit deeper than electrics, and you can pick them up at flea markets or restore for under $5.
    – dandavis
    Commented Jan 13, 2020 at 19:18
  • 13
    @dandavis fair point, but this is for concrete, which means a masonry bit and probably a hammer drill. You'd have to be quite the masochist to drill a 2 1/2 foot hole with a $5 hand drill.
    – Criggie
    Commented Jan 14, 2020 at 0:39
  • 1
    @Criggie - Agreed, but he only has 4 inches left to go!
    – Glen Yates
    Commented Jan 14, 2020 at 20:48
  • 2
    @GlenYates I don't know if you have tried using a non-hammer drill to drill into concrete, but they generally are pretty bad. A hand drill is basically "arm day" exercise for couple hours.
    – Nelson
    Commented Jan 15, 2020 at 2:42

5 Answers 5


A 1.5" hole (38mm) in concrete is beyond any conventional drill. You might get away drilling empty block, but not a foundation.

I'd suggest renting a big rotary hammer drill driver for this job. Most rental places are happy to rent you a suitable bit for the task as well, on the basis if you didn't have the tool you're unlikely to have the proper sized cutter.

It might also be a coring hole saw instead of a masonry twist drill, potentially with a water feed for keeping the dust down. The bigger ones come with a base that you bolt to the wall or floor to maintain tracking and not risk bending your tool's shaft.

Either way this is going to be a heavy tool to hold that is enormously loud, and will have high vibrations to the user and the structure into which you're drilling.

From https://www.instructables.com/community/How-to-drill-a-4-inch-hole-in-concrete/

More info at https://www.instructables.com/community/How-to-drill-a-4-inch-hole-in-concrete/

Also, consider that you risk running into reinforcing rod (rebar) in a foundation, so your cutter will have to deal with steel as well as concrete.

Once the hole is done, you will absolutely have to clear it of dust and then seal the fresh surface - cut steel will need rust protection and the concrete will need silicon of some sort.

Consider also what other concrete holes you might want to prepare while you have the drill in your hands.

There's no shame at all in getting a contractor to drill your hole too - they will have the gear and probably cost not a lot more than a rental.

  • 5
    I know this doesn't answer the question as posted, but it does address the job at hand.
    – Criggie
    Commented Jan 14, 2020 at 0:53
  • 29
    This is the correct answer. Use the proper tools for the job; don't wing it.
    – SQB
    Commented Jan 14, 2020 at 10:23
  • 1
    An SDS bit is adequate for this job, providing the bit is long enough.
    – cutrightjm
    Commented Jan 15, 2020 at 1:49
  • 3
    The last sentence should be the first sentence. By the time you factor in the rental cost (or the cost of the drill that you'll wreck trying to avoid the rental cost), cost for the bit, and all the other "extras", there is not much savings to be had. This job is very easy to underestimate (it's just drilling a hole, how hard can it be?? haha ok.)
    – Z4-tier
    Commented Jan 15, 2020 at 15:06
  • 2
    @Z4-tier And afterwards, "Who knew drilling a hole could be so hard?"
    – Michael
    Commented Jan 15, 2020 at 22:18

If you are using a core bit with a shaft for which there's an extension, you'd probably have thought of that already. As far as I know there's no extension available for SDS plus or SDS max shanks. There are extensions for the "rope" threads and for the 5/8" and 7/8" threads on diamond core bits.

The John Henry method is to drill as far as you can, then smash around the hole with a ball peen hammer so you can put the chuck in the hole another 4", then drill the rest of the way through. This comes out as pretty as it sounds. Actually if you need another 4", you might need a chisel, or a chisel attachment on the rotary hammer to take out what you need to. Before you start, check the chuck end of the drill and make sure you don't have to take out an excessive amount to get the drill in another 4", really depends on the shape of the drill.

If you are using a core bit with a pilot bit or pilot rod, another way to go is get a 3' long 1/4" bit and drill all the way through, then drill as far as you can from one side, then drill from the other. The pilot hole will keep the core in line pretty well. This doesn't always work as planned, sometimes it doesn't follow the pilot hole closely enough, but it usually does. (The reason for this method is a long 1/4" bit is a lot cheaper than a long 1-1/2" bit.)

  • 4
    Rather than going "John Henry" on it, I'd make four cuts in a square with a diamond saw and knock out that area. It would look clean enough that you might get away with not actually repairing the surface.
    – isherwood
    Commented Jan 13, 2020 at 18:40
  • 10
    @isherwood - the John Henry method would of course be a minimalist method to get it done-now with what's on hand. If I am going to run for a diamond saw, I might as well get the right bit / extension... Commented Jan 13, 2020 at 18:47
  • 3
    Never heard of John Henry, but he sounds like a practical DIYer!
    – AndyT
    Commented Jan 14, 2020 at 12:24
  • 5
    @AndyT the reference is to folklore hero John Henry, whose job was to chisel holes in rock to place explosives for tunnel blasting, and was known for being able to do so at speed.
    – Carcer
    Commented Jan 14, 2020 at 12:49
  • 3
    SDS plus extensions do exist. uk.milwaukeetool.eu/sds-plus-extensions Commented Jan 15, 2020 at 18:49

I have extended drills for one-off jobs by soldering (or welding / brazing) a piece of pipe (of a suitable diameter) to the end of the drill and putting an old drill into the other end of the pipe for the drive end.

Need to go slow as they tend not to be perfectly straight :) but have got the job done...

  • 2
    You are clearly a member of the Hack Mechanic Club! :-) Commented Jan 15, 2020 at 16:19
  • 2
    I remember my old boss gas-welding a drill bit onto a pipe. He did the welding on a switched-off lathe to maintain alignment, with the pipe through the bore/chuck, and the drill bit held backward in a large tailstock drillchuck. Worked well, was used for de-rusting the inside of radiator pipes. Only downside, it was apparently hard to put a fresh grind on a drill bit that is now 12 feet long !
    – Criggie
    Commented Jan 16, 2020 at 0:35

You could drill another hole from the other side. It takes a bit of careful measurement to get the starting points lined up, and you have to make sure to keep the drill straight...

To make sure you're lined up, you could drill a small pilot hole with a drill bit slightly over 4" long. If your pilot hole connects with the hole from the other side, you'll feel the resistance fall away and you're good to go with the large drill bit. If you're off, well, a small pilot hole is easier to fill than a large one.

  • They did that for the channel tunnel 15cm out when they met - blamed it on converting between English and metric... :) mind you that was over some 31 miles... and some are challenged getting holes to meet on a tiny wall...
    – Solar Mike
    Commented Jan 16, 2020 at 16:58

For a hole that diameter in concrete I'd strongly recommend a diamond core cutter. If it's a one-off operation, you can hire one, or you may even find a tradesperson who specializes in drilling such holes for builders and DIYers, using the right tool. Google is your friend.

If it were brick or block, I'd look at buying a "longest" small diameter drill (cheaper) to drill a pilot hole, and then widen it with the fat drill from both ends meeting in the middle. This also makes both external faces neater (no "crater" around the pipe). The technique will work with concrete. It's just the amount of noise and vibration it will cause that makes me dislike the idea. (Also the possibility of getting a broken wrist, if the drill snags on a steel rebar and the clutch is imperfect. But I know a foundation is usually just poured concrete without reinforcement).

If your fat drill were almost long enough you could try drilling all the depth you can from the side where cosmetic appearance matters. Then insert a mild steel rod to the full depth of the hole and whack it hard with a club hammer. If you are lucky a chunk of masonry and plaster will fly off the other side. But again, its more of a (somewhat bodgey) technique for brick or block walls.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.