How do I hang heavy things (mirrors) on walls?

Hanging items can be done the same as if it was a concrete block wall. Use masonry nails that are specifically designed to grip into concrete.

Repairs can be made by adding plaster to the existing wall after you remove all the damaged and crumbling plaster. Then paint.

Do you want to hang things on this wall or do you want to repair the crumbles?

First, find the tenants that have been there a long time- they know what’s going on.

There has to be some flat studs on the concrete for the electrical boxes. Check by turning off your circuit breaker and take the outlet out of the box and look at how the box is fastened to the wall.

If there’s no wood studs.

If you want to attach wood studs to the concrete walls, then you’ll have to remove the plaster and attach them with something like Tapcons. You’ll need a strong drill.

To patch the plaster, is it actually plaster, like Plaster of Paris? Find out what it actually is from your neighbors.

Re: the crumbles, are they damp or moldy looking? If so, that’s a problem, that’s too big for a DIY. As in water penetration into the building.

Drywall compound for surface blems. To hang heavy things, I'd use a concrete bit in a drill so you can insert a screw.

Drywall compound will repair surface blems. To hang heavy things, I use a drill with a concrete or metal bit so you can insert a large screw.

To hang anything in plaster need to predrill hole then use molly bolts so plaster does not crack; need to remove all crumbling plaster and repair holes Repairing plaster walls videos https://www.youtube.com/results?search_query=DIY+repairing+plaster+walls

Use command picture hangers. Get the heavier ones. My daughter attached her bed headboard to the wall and it worked great with no holes.

Thanks for all the answers , they sound good