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Drilling into Concrete Fence Post

  • 29-07-2022 4:16pm
    Registered Users Posts: 7,263 ✭✭✭ funkey_monkey

    I've got some concrete fence posts in garden and I need to attach some brackets to it to hold a fence rail - no suitable holes on post currently.

    I get that this question might be a bit vague, but anyway...

    Can you drill a 10mm hole into a concrete fence post (75mm x 100mm, hole central in 75mm face) for an anchor bolt without affecting its integrity to any discernable level?

    Or would you be better to make a |_| shape bracket and drill right through the 100mm face and put a washer and nut on the opposite side?


  • Registered Users Posts: 1,527 ✭✭✭ tphase

    I'd be inclined to drill through. An anchor bolt might cause the concrete to crack. You might get away with using a smaller bolt (or a couple of smaller bolts) if that's an option

  • Registered Users Posts: 7,263 ✭✭✭ funkey_monkey

    The bracket surface area means that there would be insufficient gap for two M6 without being a bit too close to the sides for my liking - I'd be concerned about it bursting outwards if I used two anchors.

    Without knowing the loads for a M6 or a M8 I suspect that they might even suffice on their own as an anchor. However, the safest way is to use a through bolt - it just make a lot more work for me making the brackets.

  • Registered Users Posts: 1,693 ✭✭✭ mulbot

    Have drilled into my posts with a 10 mm anchor, no issues at all, drilled a 6 mm hole first, no cracking. Have a hammock hanging from one, gates hanging off another

  • Registered Users Posts: 2,585 ✭✭✭ chooseusername

    Sorry funky, that was a fail, I was trying to suggest something like this;

    Or like @tphase suggested drill through the post and use m8 coach screws through the post and into the rail.

    Post edited by chooseusername on

  • Registered Users Posts: 7,263 ✭✭✭ funkey_monkey

    Might have to expand on that diagram @chooseusername . What the bit to the left?

    I was planning on a |_| to fit against post and then drill through. There would be two 'winglets' on the front face for the fence to be bolted to.

    Giving something like: _|__|_

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  • Registered Users Posts: 1,034 ✭✭✭ monseiur

    The trick when drilling a concrete post is avoiding the steel re bar, hitting this bar with a masonry bit may ruin it. If post has 2 re bars they will be off centre so it may be safe to drill right thru' the very centre.