I have an apartment that used to have an extra room that the neighbor next door has incorporated into their apartment. The wall between the apartments is a standard interior concrete wall that has been fitted with two or three layers of plasterboard when the room was partitioned. Now I want to put up quite heavy bookshelves on the wall. What is the best way to do this? I assume it will require rather long plugs to go through the plasterboard into the concrete behind?