I'm trying to understand the construction of a wall in my basement in order to determine how best to attach French cleat hangers to it. The studs I have been able to find with my stud finder have appeared to be irregular distances apart (anywhere from 6" to 26") so I suspected something unusual was behind the drywall.
Taking off a section of drywall revealed this. It is some kind of fairly crumbly 1/2" thick cement board over what appears to be plywood. The hole in the lower right was already there when I took the drywall off, though I enlarged it a bit to expose the plywood behind.
My first question is: what is this material?
Second: it clearly has no structural value given how crumbly it is (I can break off pieces with my finger), so there must be studs behind it. I think it is playing tricks on my stud finder. Any suggestions for locating the studs beyond drilling a bunch of holes?
EDIT: I was able to look at a different part of the wall via the access panel for our water shut-off valve. I think I was mistaken, and this is actually a layer of plaster with the old lath and plaster behind it. As you can see, in this section of the basement a new stud wall was put up in front of the lath and plaster. It appears in the original photo that the drywall has been attached directly to the plaster on top of the old wall. Is this going to cause me problems in the future?