Drilling concrete wall-preventing blowout

[bluedog225]

I’d like to drill a 1” hole in a 10” concrete wall. Ideally, I will drill from the ”inside” to get the hole exactly where I want it.

And I’d like to avoid blowout on the outside wall. I’ll be using an SDS max drill for the larger hole.

I was thinking of drilling an 1/4” hole first. Then going to the outside wall and drilling the 1”. The 1/4” would also be a general check for rebar.

I don’t think a pilot hole would matter much in terms of drilling the larger hole.

What do you guys think?

 

[Rusted Nut]

Blow outs/spallings happened when you give the drill too much pressure. Go really light on pressure when you an inch from the other side of the wall, let the drill drill. No need for a pilot hole. If you happen to hit a piece of aggregate on the outside edge, not much you can do to prevent the aggregate from popping out, except to turn off the hammer function and just drill when you're less than an inch away.

 

[wssix99]

This is exactly what I do. I use one of my small bits to drill the hole and make sure it comes out where I want it on both sides first. I then drill the big hole from both sides and into the middle. Its always clean.

 

[rlitman]

I think the pilot hole is bad in general for SDS convential drilling. Less bad if your drill has a solid carbide tip (a rebar cutting type), but still really hurts drill progress. I do get the idea of alignment though. SDS max is a lot of impact energy on a 1" hole. Even going light on pressure, it's very easy to blow out a 1" hole with an SDS max, so your plan isn't totally nuts.

How confident are you on the thickness? Can you drill conventionally until about 2" from the back-side, and THEN use the 1/4" pilot to locate your hole on the outside?

 

[bluedog225]

Thickness is fairly certain. I can use a regular SDS also. Should not be a problem to stop an inch short. Though I won’t have the certainty of hole exit location.

Pretty sure all my big drills are carbide.

 

[The Cobbler]

most thru holes I have drilled in block or concrete walls have been done from the inside out to locate using a smaller bit, then finished from the outside in with the correct size , usually a 4-1/4" core bit in my cases

 

[rlitman]

Thickness is fairly certain. I can use a regular SDS also. Should not be a problem to stop an inch short. Though I won’t have the certainty of hole exit location.

Pretty sure all my big drills are carbide.

If you have SDS+, that's not going to blow out much at 1" diameter.

They're all carbide to some degree, but the difference I'm talking about is if there is a strip of carbide going across the tip (perhaps with some extra carbide for the other two points), or is the entire tip one big hunk of carbide brazed on. example:

most thru holes I have drilled in block or concrete walls have been done from the inside out to locate using a smaller bit, then finished from the outside in with the correct size , usually a 4-1/4" core bit in my cases

With core bits, it usually makes sense to have a pilot hole.

 

[Nobody-named-Olli]

One hole, one time?

Get on amazon, buy a cheap 1” diamond core cutter that is long enough and comes with a shaft/adapter. Drive it with a(ny) drill that has a second handle and is capable of doing rpm somewhere in the ballpark of 12xx to 1300.

It won’t have a pilot bit. Either use a template screwed against the wall or start the core cutter at an angle and then pull straight, while continuing to drill.

Do not rush/ press, just let the cutter work = clean hole.


While I absolutely don’t recommend pilot holes in concrete, it is done from time to time. They generally don’t do any good because, for example, a 1/4” pilot hole will not do anything to guide a 1” bit. It’s more of an “assurance” your angle is right/ your coming out in a convenient spot. The final hole will not have the same center as the former “pilot hole”. I can almost guarantee that

Kind regards,
Olli

 

[rlitman]

One hole, one time?

Get on amazon, buy a cheap 1” diamond core cutter that is long enough and comes with a shaft/adapter. Drive it with a(ny) drill that has a second handle and is capable of doing rpm somewhere in the ballpark of 12xx to 1300.

It won’t have a pilot bit. Either use a template screwed against the wall or start the core cutter at an angle and then pull straight, while continuing to drill.

Do not rush/ press, just let the cutter work = clean hole.


While I absolutely don’t recommend pilot holes in concrete, it is done from time to time. They generally don’t do any good because, for example, a 1/4” pilot hole will not do anything to guide a 1” bit. It’s more of an “assurance” your angle is right/ your coming out in a convenient spot. The final hole will not have the same center as the former “pilot hole”. I can almost guarantee that

Kind regards,
Olli

If you have the diamond core cutter, you could always use the 1" SDS drilled hole as the pilot, and use the diamond core for an absolutely clean exit.

 

[PopcornSutton]

Use the 1/4" pilot hole, marking the depth and backing off the pressure as you approach break through. Then drill the 1" from both sides. It will follow the pilot hole.

 

[jack stand]

Not that I've seen everything, but I've never seen a 10-12" long 1/4" masonry bit. Maybe a 3/8".

 

[whateg01]

The final hole will not have the same center as the former “pilot hole”. I can almost guarantee that

It will follow the pilot hole.

I guess ymmv?

 

[Nobody-named-Olli]

As usual, when asking a question on the internet.

Kind regards,
Olli