Fence post anchor bolt sheared in concrete help!

[lozcozard]

Post snapped in storm other night. It was originally concreted into a thick concrete retaining wall. I think my only option is use post anchors bolted into concrete.

got some Dial 6.8mm x 100mm coach screw and nylon plugs that require 10mm drill.

So drilled 10mm down to 100mm. Hammered plugs in. Upon screwing the screw 3/4 down it sheared.

So I have two issues... sheared screw deep in concrete and how to deal with these screws that say a 10mm drill which clearly are too tight and so shear.

For the sheared screw I think I’ll try drilling a new hole in the anchor I can’t see me getting that screw out.

but what do I do about shearing screws? Are Dial just low quality or are they not suitable for concrete? Shows brick on the packet. Drilling 12mm hole I assume is too wide then. But 10mm clearly is not big enough even though manufacturer says that. Don’t get it.

Thanks

 

[JohnD]

don't follow what you mean. photos and/or diagram may help. You mean a wooden post, and the stub is embedded in concrete? Did it rot a few inches above ground level?

Sounds to me like the bolt (screw?) was too tight in your hammered plug.

What dimensions plug?

How did it break?

 

[blup]

Dial is a B&Q brand so quality might be an issue, Fischer is a better bet.

That said you might not have removed all the debris from the hole you drilled, causing the screw to shear from over tightening when it couldn't travel further.

It is not uncommon for long fixings to get "stuck" by expanding the plug before it is fully home.

Blup

 

[lozcozard]

@JohnD the old post in concrete rotted abs snapped. So I sawed that off level to the concrete then screwing an anchor down for the new post. Screws sheared as I’m screwing. Plug is 10mm x 100mm. Screw was 6.8mm x 100mm for the plug. 10mm hole was drilled for the plug as per what the packet of screws said.

@blup i gut all the debris out because the plugs initially would go all the way in even though I drilled. There was always debris at the bottom. So didn’t a while cleaning the holes out so the drill would go in and out smoothly. So I don’t think there was much debris.

 

[lozcozard]

Pics of the old post snapped, concrete retaining wall with couple rows bricks on top. Don’t have pic of holes I’ve drilled.
I’m trying to drill a post anchor over the old post. So screws go into that big retaining concrete wall.

 

[lct]

I would find a spot to do a couple of test holes in. Do another 10mm and make sure the debris is all out of the hole. Maybe run the bit in and out a few times to make sure it's a 'loose' 10mm. And if you have a 12mm bit then try that as well. You will know from how the screw tightens down if you have a good bite. Whether or not the eventual 4 screws will be good enough to hold a fence post in place is a different question.

 

[Tigercubrider]

I would dig the old post rotten wood out with a chisel.
Do you own the lower ground and short wall?
You could refit a wooden post into the cleaned out hole, then support it with two 45° timbers either to the higher ground surface or the wall top. The angle could be made steeper.

 

[lozcozard]

@Tigercubrider i don’t own the lower ground no. I don’t know if the retaining wall is mine or the neighbours! Perhaps mine if the fence is on top of it. But the brick is the other side of the fence so don’t actually know what’s mine. Best I don’t do anything the lower side of the bricks.

I’ve decided to try this expansion bolt https://www.amazon.co.uk/dp/B086BBG4WR/. I imagine they’d not break as easily. I don’t want to risk breaking even more screws even I do test like @lct says. I’d be in bigger trouble with more snapped bolts.

Removing the old post may be a good idea. Might be hard work though. So I think this will be a good last resort if the expansion bolts have issues too.

Thanks

 

[oldbutnotdead]

How near the edge of the concrete will the bolts be? Less than 100mm and its good odds you'll crack the concrete...
Not sure that bolting the thing down as the sole means of fixing will last long, there'll be a lot of leverage exterted on the bolted plate. Remember if one post has failed, others fixed the same way at the same time will also be failing.
Extracting the rotted bit could be a pain, fire might be your friend.

 

[lozcozard]

@oldbutnotdead its not near the edge it’s in the middle maybe 200mm either side.

the other posts are all concreted in.

I’ll see if I can remove the wood but I imagine it would be quite difficult to chisel out wood from a75mm x 75xx opening. Guess I’ll need a long chisel or similar tool and chip downwards not across. Maybe I could shred it using a drill.

 

[lozcozard]

Update on what I did in case anyone else has same...

Decided not to use post anchor because I too think in winds the bolts will eventually pull out.

Chiselling old post out not possible as it’s too deep in the hole
Crow bar on own to chisel and pry and shred was a nightmare
Drilling with wood drill to create holes then crow bar was better but a nightmare

in the end I got a long masonry drill I have to go through house wall, so about a foot long, and with my SDS drill just pummelled it all to bits and this really broke it up much better and it was out in no time.

dropped new post in and filled gaps round edge with postcrete. All seems ok now.

thanks for help