I'm trying to hang a 4Kg electric guitar on a wall that sounded hollow however when I drill in after just under 4cm the drill head hits what sounds like either brick or concrete. I've bought expanding metal rawplugs that are 4cm long that look like:
But these now can't be flush with the wall to expand correctly. I've also bought self drill metal plugs which are 31mm in length and look like:
Apparently these can hold 8Kg per screw (and the guitar mount has 3 holes) so that should be fine but there's nothing on the packaging that says they will hold 8Kg per screw, that was just what I was told in the store so I'm not too confident.
I know the general consensus would be to mount these with a longer wall plug and screw into the concrete or brick behind but how do I know I am actually hitting masonry? I have a wood and metal stud finder which is not detecting any studs or live electrics but I want to be confident before attacking this with a hammer drill