How to accurately bolt post anchors to existing concrete pad

[pepsp]

I'm upgrading an existing pergola and adding a deck at the back of our house. I'm having trouble getting the diagonal locations of the post stirrup holes right compared to the locations in the pryda stirrup base so I can bolt it down. You can see from the image below the hole is not quite centred compared to the base of the stirrup.

Any tips on how to do this correctly? And how to fix the one I've messed up?

[MitchellMc · Accepted solution]

Welcome to the Bunnings Workshop community @pepsp. It's fantastic to have you join us and many thanks for your question.

You'll find larger masonry bits walk all over the place when trying to drill into concrete. I had a similar issue recently and the solution was to drill a small pilot hole around 4mm first and then follow that up with the size required.

I'd start by filling the hole which is misaligned with Timbermate 500g Concremate Expanding Cement. You'll want to use a chopstick or similar item to push the patching cement right down into the hole and then wait until it has fully cured before continuing. Once it has cured fully you can re-attempt the hole.

Let me mention the helpful @TedBear to see if he has any other solutions or techniques to try.

Mitchell

[pepsp]

Thanks Mitchell this is very helpful. I wondered if a template would make a difference so you can get right over the hole to mark it and start it.

[TedBear]

Thanks for the reference Mitchell, but I can only agree 100% with what you are suggesting. 

The template idea is a good one too. Make the holes in the template the size to suit the pilot drill, not for the final drill size. That one should just follow down into the pilot hole.

[pepsp]

Excellent thanks @TedBear  I'll give it a try.

Regarding fixing the post anchors down, which is the better option: ankascrews or chemset bolts? I found ankascrews pretty awkward to get in with only 65mm clearance on the anchor and wondered if chemset is going to be easier? @MitchellMc 

[MitchellMc]

@pepsp,

Chemset could possibly by easier and both options are suitable for this application. However, I generally use Dynabolts as they're quick and easy.

Mitchell

[Noyade]

For me, you're so close, I'd be using a round file and extending the hole - re-bolt with a larger washer.

Or, take it off (the stirrup) and with pencil and paper mark the exact size/location of the holes in the concrete - rotate the stirrup 90 degrees, mark it and re-drill new holes in the metal.

Cheers and good luck.

Graeme.

[pepsp]

The re- do came together nicely thanks all. And now I'm wondering- how do I drill a straight hole through the post to bolt it in place? @MitchellMc 

[MitchellMc]

@pepsp,

Take something that is around 5mm thick and flat. Place it on the stirrup where the post will sit. This is used to create a space where water can not seep into and encourage rot. Put the post into the stirrup on top of the spacer. Mark where the holes are on both sides of the post. Remove the post from the stirrup and place on a flat surface. Drill from one side half the depth of the post and then flip it over and drill to connect the hole from the other side. This splits the difference between how off centre you are.

This is the method I use and it has served me well. Let me mention some of our woodworking experts @Poppop, @r23on and @woodenwookie to see if they have some other methods.

Mitchell

[woodenwookie]

Don't use a template. I had an issue installing a roadside mailbox for work. I made what I thought was a template only for it to be completely way out of whack.

Work with each piece separately as you can't guarantee that the holes will be drilled exactly the same for each leg therefore a template will be useless. I found this out the hard way.

Drill the first hole then put the bolt in to align it all. Then as was mentioned use pilot holes before fully drilling out. I like to work on the diagonals because it gives you a nice alignment as you go.