Ok, I've now inserted a tape measure into the hole where the TV cable comes in and hit what I think is the external tile at 140mm. I've also used a longer drill bit in one of my test holes and hit something at about 40mm (Notch7's plywood?). I'm guessing it's going to be 18mm external grade...
Hello People, I'm trying to fix a TV bracket to the side wall of a Dormer window. It is lined with what appears to be Celotex. As can be seen from the photos I have drilled into the plasterboard at regular intervals but have not hit any wood. The property is about 10 years old. Can anyone...