Concrete drilling- what's your method?

[sw_ross]

When I have to go through concrete, block, or brick I generally use a 16"x3/8" pilot bit, then I use a 1" bit (for 1/2" EMT) to finish out the hole.

Problem is, with either bit I can get varying amounts of "blow-out" as my bit goes through the wall. Definitely doesn't look as clean as I would like. I was wondering about other methods like using the appropriate size core bit to drill in from each side and then finish the wall with the actual drill bit (1" or 1 3/8")?

Mostly I'm looking at holes for 1/2 & 3/4" EMT.

Also wondering if anyone has experience with the dewalt 60v SDS-max drill? I'm wondering about being able to use it for 2 3/4" core drill (max) and driving ground rods.

Thanks!

 

[LarrywdH]

as far as the blow out, don't drill all the way through from one side, go to the other side and find where the pilot hole came through and go the other way

 

[Strathead]

as far as the blow out, don't drill all the way through from one side, go to the other side and find where the pilot hole came through and go the other way

While better, you will often get too much blow out even from a pilot bit to be hidden.

 

[sw_ross]

Bind up

Bind up

A couple days ago I had to run conduit through a block wall. It was 12" thick with concrete in-fill. I drilled my pilot bit. Then drilled about 8" in with my 1", went around to the other side to finish out the hole, when the two hole met they were slightly off angle with each other causing the drill to bind up.

I was able to clean out the hole but the conduit needed to be tapped in with the slight cant in the hole.

Actually, my pilot bit is what caused the blow-out. Not sure how to overcome that...

 

[Strathead]

A couple days ago I had to run conduit through a block wall. It was 12" thick with concrete in-fill. I drilled my pilot bit. Then drilled about 8" in with my 1", went around to the other side to finish out the hole, when the two hole met they were slightly off angle with each other causing the drill to bind up.

I was able to clean out the hole but the conduit needed to be tapped in with the slight cant in the hole.

Actually, my pilot bit is what caused the blow-out. Not sure how to overcome that...

frankly, I think the only real solution is to use a core bit all the way through. Otherwise, you can use a larger bit to alleviate the slight cant you are referring to. You can drill from the side that has high visibility and live with it. You can carry Quickcrete patch and patch.

 

[JFletcher]

to reduce blowouts and the size of them, the last half inch or so of drilling, I switch the drill to high speed and turn off the hammer mode. I also prefer the Hilti crosshead bit. Eta: I never use a pilot bit when drilling concrete.

if you hit a piece of aggregate near the edge, you're going to have a blowout, and some things, like brick, tend to chip no matter how careful you are. Most times I drill toward the side that will be least visible, or have the blow out covered by a junction box.

no experience with that 60 volt cordless you mentioned, however if you have any number of holes to drill, corded is the way to go

 

[MTW]

A couple days ago I had to run conduit through a block wall. It was 12" thick with concrete in-fill. I drilled my pilot bit. Then drilled about 8" in with my 1", went around to the other side to finish out the hole, when the two hole met they were slightly off angle with each other causing the drill to bind up.

I was able to clean out the hole but the conduit needed to be tapped in with the slight cant in the hole.

Actually, my pilot bit is what caused the blow-out. Not sure how to overcome that...

Use a 1/4" pilot bit with a high speed, short stroke hammer drill, I use an ancient AEG 1/2" drill and an 18x1/4" Pilot. This will leave a very superficial blowout size.

Measure the pilot hole center from the corners of the block, and mark down on a cheat sheet. Remember when you get to the other side to mirror the measurement, from the same corner of the block.

Go to the other side and locate the block with the pilot hole. Use the cheat sheet measurements, to mark the actual center, as the 1/4" bit normally wanders a bit. Make another 1/4" pilot hole, in the correct place if it wandered.

Then finish up with the big drill from both sides. I use a large frame Hilti rotary hammer and Hilti bits, it has plenty of power to go through, even if the hole is misaligned.

A bit tedious, but will have no blowout, unless you were way off with the pilot shot.

One other tip. I carry a cheat sheet with sketches of different block types, concrete and cinder, 3 and four 4 web blocks. The sketches have the dimensions marked of all of the web locations, from the ends. In this way the layout can be done to avoid placing your hole where the internal webs are. Intersecting the web, even partially, will ensure that your bit gets pushed sideways while drilling.

 

[StarCat]

Carbide Hole Saws

Carbide Hole Saws

Carbide hole cutters make VERY clean penetrations through Cinder, and Concrete and can be run wet when needed.
Some I have seen can be run with hammer.
Pilot bit should be 1/4" when predrilling long, same as arbor pilot bit.
Looking at the sides of various buildings, its always obvious the " rip and tear " methods that do not produce clean results.

 

[K8MHZ]

I was drilling a pre-cast wall once for 3/4" conduit. I used a 1/4" seeker bit with the intention of drilling the larger hole from both ends. I was VERY careful. Nonetheless, the seeker blew a 3" hole out the other side. Probably hit a small rock and pushed it out.

 

[junkhound]

In seismic area here, so seldom see concrete block.

In concrete, use a spline drive bosch bulldog hammer drill, never bother with a pilot hole as often have 8" or 12" walls to go thru, in deep holes, getting a pilot stuck is a pain.

50+ years ago, once drilled a 7/8" hole thru 12" with just a 1/2 drive regular drill, took me about 2 hours vs. nowadays 3 minutes with the bulldog and a good bit.

I watch ebay for used bits, brand and close inspection of the bit photos and have never been disappointed at 10 cents on the dollar for good hammer drill bits. Sharpen on green carbide or diamond wheel. If not photos of used bits, never buy.

 

[JFletcher]

eBay items can sometimes be great purchases... The drill bits you mentioned, sometimes they just need a little bit of dressing and you can save $100 a bit over new. also I routinely look for Firestop on there, I have bought putty pads for a dollar a piece, and tubes of Hilti fs-one that are normally $18 a piece for $50 a case shipped. can often find Surplus Leviton Cat6 Keystone's for like $2 a piece instead of $7 a piece new. Back on topic, the carbide tip core bits are expensive, however they will drill the cleanest holes

 

[gino748]

I’ve successfully used lead anchors, drilled into the brick, to hold shelves on the party walls of my house, where the plaster is applied directly to the brick. The shelves fell on my first attempt because the anchors I used were too short and only penetrated the plaster. Longer lead anchors did the trick. If you’re going to use anchors on exterior walls they’ll have to be VERY long to penetrate the plaster and lath, go through the narrow air space, and penetrate the brick. I wonder if anchors like that are available?

 

[Knuckle Dragger]

Pilot holes are helpful when you want to drill from both sides or not 100 percent sure of the end result.
When drilling a hole I place very little pressure on the drill when getting close to penetrating the wall to help reduce the blow out.
It's crap shoot on the end result.