I'm trying to work out the construction of a wall that partitions two flats (maisonette). Most things on the internet deal with internal walls (with wood studs, found with a stud finder), or solid external walls. However this is kind of both, as it's internal, but partitions two separate residences.
The odd thing is that the stud finder (a powerful magnet in this case) finds nothing. But does find studs easily on the adjacent internal wall. Using the tapping technique I can find parts that sound solid, but not in vertical runs. As I tap across, I can find a solid sound, but then as I tap upwards the sound changes to hollow, and then solid again, alternating. I've drilled into the "solid" part, and couldn't discern wood, and appears to be just powder coming out. Unfortunately there's no wall sockets to inspect either. Construction was in 2013 in the UK (if that helps).
Anyone got an idea what's behind this wall? I'm trying to put up a heavy load bracket. Any help greatly appreciated!
Edit: I'm starting to think it may be a "Dot and Dab" fixing of plasterboard over a solid wall. This would explain what I'm seeing/hearing.