On the plastered walls were several installations on the outside. These bits made it through the 40 year old cured compound, between and through the lugs, into the interior with no problem. I took great care to keep the drill straight and aligned with the hole to be drilled. Although I haven't clicked one yet, I don't think it will be very difficult. The lugs are showing some wear after this work but for the price I didn't expect the set to last a lifetime.