concrete fence posts

[larco]

Hi,

I would like to attach some external plywood against some concrete fence posts.
I would like to drill three holes in each post but i was wondering which bit size i should use? I have an sds drill. Can i insert a rawplug in the holes?

Also should i drill in the middle of the post?

many thanks

 

[Deluks]

Better to use without hammer action and use a new quality bit like the irwin or bosch cordless multi bits. Plug and screw should work as normal, or use concrete screws (aka frame screws) which go in without the need for plugs.

Middle is fine but beware of hitting any rebar, if you do then you should switch to a hss bit (will probably be shagged afterwards) for going through the rebar.

With the multi material bits you should still be ok going through the rebar but drop the speed accordingly.

 

[larco]

thanks for the reply.

can you advise me on the drill bit size to use?
Also if i use plug and screw what size should i use?

thanks

 

[ladylola]

Use brown plugs and a 7mm drill bit which will suffice for number 10 and 12 screws. May also be an idea to use repair washers ( large washers the size of an old penny) as the ply will be subject to a lot of force from the wind and the washers will help stop the screws from pulling through the ply.
An alternative method would be not to drill the posts but to wedge in rails with a lath on its face and screw the ply to them lipping it over the concrete to pinch it and hold it firm.