Drilling into hard plaster?

[juliant]

I need to drill some holes in a (fairly recently built) wall that is plaster over blocks, but my problem is that the surface few mm is rock hard but quite brittle. Once you get through that layer it is fine, but on previous occasions I've sometimes ended up with a patch of the surface cracking off. Because of where the holes are going to be, I don't want that to happen this time.

Any suggestions for the best way to get a neat hole through the first few mm?

Thanks...

 

[dann09]

juliant,

On medium speed, use an old, HSS, small diameter bit, just penetrate (drill) into the block, and then go with a larger HSS bit to the same depth.
Now use the req'd diameter tipped bit to open up your pilot hole to what ever depth and diameter your fixings req.

Note: modern houses are mostly dabbed-on plaster board - are you sure that you have plastered block?

 

[juliant]

Thanks for the reply...

And yes, I am sure about the construction: watched it being built

jt