SF-02Confirm the wall is solid brick or blockTap the wall across a wide area. Solid brick or block sounds dull and dead everywhere, with no hollow patches. Drill a small pilot hole about 10mm deep — solid masonry gives brick-red or grey stone dust straight away. If the wall sounds hollow, or the pilot hole breaks through a thin board before hitting anything solid, you have a stud wall or dot-and-dab. A safe must not be hung on plasterboard or studs alone — the fixings need to reach solid masonry behind. If it's dot-and-dab, measure the gap behind the plasterboard so you can choose fixings long enough to pass through the board and dabs and into the brick or block.