Drilling a pilot hole for a cement screw - should I go smaller than suggested?

[AVR2]

I'm going to be using cement screws to attach wooden battens to some concrete fence posts. I've never used cement screws before, and the ones I bought say they need a 6mm pilot hole.

I experimented by drilling into a breeze block and winding the screw halfway in. With a 6mm hole, there was a little bit of play in the screw when I tried wiggling it. I tried a 5mm hole, wound the screw in to the same depth, and this time there was no play when I wiggled it.

Would that just be because breeze block is more friable than concrete? Should I stick to the recommended 6mm pilot hole when I drill the proper holes in the fence posts?

 

[Mr Chibs]

Think 6mm bit is what I use for masonry screws. Occasionally you may get a loose fit... bamboo bbq skewer or matchstick placed in hole will make the drilled hole useable again.

 

[^woody^]

Do what works. If it's 5mm, do 5mm.

 

[blup]

Check what the manufacturers specify, different manufacturers specify different hole diameters, sometimes varying with the material being drilled.

I've found a 5.5mm pilot hole in brick will take a 6mm concrete screw but it's tougher to drive the screw home because it's biting into the brick. That was on a key safe that needed to be tight to the wall. If you are drilling deep into a concrete fence post you might hit the rebar that reinforces it.

Blup

 

[lostinthelight]

As I said in op other post, I would use the lighter weight which require a 5mm pilot. If the hole turns out a bit big then you've got the safety net of the heavy duty screws or use plug and screw.

 

[Notch7]

Lightweight blocks and concrete posts are chalk and cheese.

concrete screws tend to need a 6mm hole in hard brick and concrete. 5.5mm hole in softer bricks.

concrete posts also have reinforcing steel wire inside…..I actually wonder if you would be better with plugs and screws.

you will need an SDS drill unless you want to be drilling for a looong time

 

[foxhole]

Why are you battening posts?

 

[lostinthelight]

Why are you battening posts?

https://www.diynot.com/diy/threads/...concrete-screw-which-one-should-i-use.574528/

 

[foxhole]

https://www.diynot.com/diy/threads/...concrete-screw-which-one-should-i-use.574528/

Will need to be high. Chased a fox from my garden , cleared a 6’fence from my lawn which is 2’ below ground level and 6’ from fence, didn’t touch the fence .

 

[opps]

Or you could try some of the tips in the following

https://mybackyardlife.com/can-foxes-climb-fences/