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Old 06-14-2018, 12:01 AM   #1
colesfamily
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Default Drilling Granite

Greetings Forum Members,

Can someone tell me how to drill into granite? I had a granite mail box post installed and I need to install a mail box bracket into it but I'm not sure what type of drill bit to use and whether or not to use a hammer drill or regular drill etc. So if you have actually done this project yourself please advise, it would be greatly appreciated.
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Old 06-14-2018, 06:04 AM   #2
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Sorry didn’t mean to hit the “thanks” button.

Get a masonry bit for the size screw-anchor you’re going to use and of course use a hammer drill on high speed.
Your local hardware store will point you in the right direction for bit and anchor sizes.
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Old 06-14-2018, 08:29 AM   #3
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I had to do the same project five years ago. I bought a masonry bit and rented a hammer drill at the local HW store. A hour later I had made very little progress. I went back and asked if there where other options and I ended up leaving with a rotary hammer. The job was done in 30 minutes. Spring for the larger tool.


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Old 06-14-2018, 09:24 AM   #4
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I do not recommend using the “hammer” feature when drilling through cut and finished granite. Turn the hammer feature off and use rotary only. It may take a little longer but A LOT less chance of cracking the granite.

Good Luck!

Dan
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Old 06-14-2018, 09:31 AM   #5
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Can be done Fred Flintstone style with a 12" long, 1/2 or 5/8" diameter, hand held, steel STAR drill, and a 2 1/2-lb mason's hammer. Simply whack away and turn the star drill a wee bit with every whack-whack-whack...... Fred Flintstone style ...... this really works in gray NH granite .... yabba-dabba-doo!
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Old 06-14-2018, 09:54 AM   #6
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Much of the answer depends on what you plan to use for fasteners.

For this job, I would probably go with either lead anchors that can accept a 1/4" or larger fastener, or a 3/8" sleeve anchor. A mailbox gets a fair amount of abuse and you want something more than a simple Tapcon (IMO), and something that makes it easy to remove and replace the bracket when or if you eventually need to.

Drilling the holes should be pretty easy with a hammer drill and a *quality* mason bit. If you're drilling a 1/2" or larger hole (possible for some sleeve anchors) you might find that a diamond/carbide style core bit is easier than a masonry bit/hammer drill (you're removing less material with the bit with a core drill, goes faster). The issue with most cheaper core bits is they may not go deep enough, so you drill and then use a cold chisel to "pop" out the plug and continue drilling.
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Old 06-14-2018, 11:14 AM   #7
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Default Granite post drilling

An organization I belong to bought and installed 22 granite posts. It is (was) our intention to install black plastic chain between the posts. We have not done it yet. We also will be mounting small plaques on some of the posts.

Our supplier cautioned us that if we were to drill into the posts, we should not use a hammer drill, as Dan (I Shoot 308) said, due to a high risk of cracking the post, and to use a rotary drill only.

They also advised to seal the holes to prevent water from getting into the holes and freezing.

FWIW

Dave
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Old 06-14-2018, 11:39 AM   #8
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Also, all anchors should be kept a minimum of 2” from any edge and from each other, again this is to prevent cracking and not for structural integrity.

If it was me, I would use an epoxy anchor threaded stud of the proper size to anchor the mailbox. This will keep All pressure off the sidewalls of the hole in the granite. Expansion style anchors or “Tap Cons” exert a lot of pressure to the sidewall.

Dan
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Old 06-14-2018, 01:20 PM   #9
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Quote:
Originally Posted by ishoot308 View Post
I do not recommend using the “hammer” feature when drilling through cut and finished granite. Turn the hammer feature off and use rotary only. It may take a little longer but A LOT less chance of cracking the granite.

Good Luck!

Dan
Have only done one granite mailbox post and used the hammer drill...guess I was lucky! I have however drilled tons of masonry holes in brick, block etc. when I was doing camera installations. Thanks for the heads up!
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Old 06-14-2018, 04:05 PM   #10
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Quote:
Originally Posted by ishoot308 View Post

If it was me, I would use an epoxy anchor threaded stud of the proper size to anchor the mailbox. This will keep All pressure off the sidewalls of the hole in the granite. Expansion style anchors or “Tap Cons” exert a lot of pressure to the sidewall.

Dan
That's a good point, and part of why I recommended the lead anchors, I've had good luck with those in granite, as they handle most of the expansion issues by their own compression.

The sleeve anchors have also worked well, for me, (though I forgot to mention use epoxy with those). The sleeve anchor setup prevents you from having significant expansion in most cases.

This was also on the presumption of a 10" or so mailbox post, like you commonly see in NH. If it was something narrower, I would definitely be more cautious about expansion.
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