View Full Version : drilling into pebble aggregate

12-04-2010, 08:06 PM
I need to attach Gemini stud mounted letters onto a concrete wall covered with pebble aggregate. Any suggestions on how to drill it with minimal "walking" of the drill bit?

James Burke
12-04-2010, 08:33 PM
Center punch and then use a smaller drill to make a pilot hole before using the drill size you need.

Use a rotary hammer drill (SDS-spline drive) instead of a hammer drills that use a regular 3-jaw chuck. They have more power and the drills are a lot tougher.

12-04-2010, 09:07 PM
start by using a small glass bit just enough to get a ploit hole and use a sds (SDS-spline drive) try to use a bosch bit the are double twisted and can run longer. also recomdend for marble

surf city
12-04-2010, 09:16 PM
+1 what burke said

12-04-2010, 09:31 PM
great advice. I think this also solved some of the general problems I've had in the past using the wrong bit in my hammer drill...."borrowed" hammer drill.

John Butto
12-04-2010, 10:56 PM
Don't know how big a job it is but attach your hole pattern on a .25" thickness pvc or masonite and level your pattern to the wall and drill small tapcons in #2 of your top holes on either side to hold it in place and then the backing will keep your bit lined up so as to keep your bit "walking" to a minimum when you drill your other holes.

Sign Works
12-05-2010, 05:40 PM
great advice. I think this also solved some of the general problems I've had in the past using the wrong bit in my hammer drill...."borrowed" hammer drill.

First off you need the "Proper Tool" for the job. You need to be using a "Rotary Hammer" not a hammer drill, a hammer drill is pretty much useless when attempting to drill multiple precision holes in concrete. You don't need to spend a fortune either, you can pick up a good rotary hammer at Home Depot for example for about two hundred bucks. I've been using the Bosch Bulldog for the past 10 years with excellent results, definetly a great tool & investment. Use this on one job and you'll wonder why you ever dinked around with a hammer drill in the first place, what a complete waste of time.


As for the exposed aggregate I have found it helpful to cut a U shape around the stud hole locations in the pattern before taping the pattern in place, this way you can use a grease pencil to mark hole location through pattern and then flip up that small portion of the pattern before drilling. If you attempt to drill through the pattern as usual the bit will walk and tear up the pattern and you wont be able to determine proper hole location. Also after flipping up the little window you'll easily be able to determine if the bit will walk and you can counteract this by slightly angling the drill. Very often it is easily remedied by taking a small chisel and knocking the interfering pebbles out of the way before drilling, once again the little flap cut into the pattern allows you to remark desired hole location. Hope that all makes sense to you. I've done a ton of these installs and the exposed aggregate was on corrugated concrete walls, talk about the bit wanting to walk on ya, this is where I started cutting the flaps in the pattern as it was almost absoloutly necessary to redetermine proper hole location several times. I've also found the 2" short SDS Bosch drill bits provide a bit more control when starting to drill the hole with exposed aggregate, these are available in the 1/4" size bits at Home Depot & Lowes.

John L
12-05-2010, 06:31 PM
Good advice above. I also have always chipped out the pebbles that are in the way. The little Finestone pebbles have nice bounce too (!) so watch any windshields below. We still have a star chip in a bucket truck windshield from me.