I’m planning to make some floating shelves 150 cm wide and 30 cm deep.
I want to mount them on a wall that has a plasterboard of thickness 13mm behind which is a plywood backing of 15mm according to the details provided by the contractor (see the attached image). This construction was apparently intended for hanging TVs and they recommend using wood screws that are not longer than 30mm.
One of the shelves will have my record collection which could weigh between 25-50kg. What are some options for hardware I can use to mount the floating shelves?
Your last question is a good one. I have no idea - I’m pretty new to this stuff. What is normally used to keep a wall from flexing?
Studs. No, seriously. I have floating shelves that hold stacks of ceramic plates and bowls, and I made sure to screw into as many studs as possible.
If you can't, and sometimes you can't, I recommend using these drywall toggle anchors. They've been fantastic. When I couldn't find a stud but wanted more support points on the shelf hangers, I used those. Note that I do recommend marking the orientation of the toggle on the head of the anchor, because you'll want it to be as vertical as possible.
Ah gotcha. Well I’m pretty sure there are studs on the right half of the wall (the left half has space for a pocket door). I think there are two but my stud finder is not very good and I’m not sure if they’re wood or metal studs.