Drywall – Weight Capacity for Hanging from a Drywall Ceiling

Go ahead and place the drywall over the top edge of the crown moulding. Sounds like the wall was already re-plastered with it in place. If you tried to remove it, you may end up re-doing the walls as well. Even forgetting that, it's almost impossible to remove moulding without sustaining some loss. Without replacement material available, removal with intents of preservation is extremely risky, especially with stain grade material. You don't want to go there.

If your joists were flat, you'd still only need to shim down the first 4 feet or so along the walls, no one will see the resulting slight slope. Keep this in mind when planning your shims. It doesn't have to be perfectly flat, unless that gives you pleasure. You also don't need to shim to completely fill the gap. An 1/8" gap makes a clean shadow line that is not detrimental (assuming it is perfectly uniform) at all. It also makes finishing easier. The taped joints of drywall are normally not perfectly flat, despite the tapered edges. There is a slight bulge which is usually invisible. But against straight moulding, depending on the profile, this bulge may be visible. You might consider grinding down the edge tapers at the board corners against the wall so the joint tape can be completely buried and the yet the joint against the moulding can still be perfectly flat.

You will NOT want to support your 78 1/2 inch rod from the drywall alone. Drywall fastened up to the ceiling is a pretty good challenge just holding up it's own weight then yet you trying to add 70 pounds to that.

So what you want to do is to locate the support members (usually called ceiling joists) to which the drywall is attached. You would then want to use screws that penetrate through the drywall and and up into the support member to hold up the brackets for your rod. For most ceiling supports the members will be found to be 16 or 24 inches apart so you should be able to find 5 or more support points for the rod if it is running across the direction of the support members. If the rod is running in the same direction as a ceiling support member then you would attach the rod support brackets at 4 to 6 locations along the same support member. In this latter case it means that you cannot locate your bar just any old place but directly under a ceiling support member.

Finding where the ceiling joists are located can be done with a stud finder tool. A simpler scheme is to get a strong magnet and scan it across the ceiling looking to find the steel nails or screws that are holding up the drywall. Each located screw will be at a point just under a support member. Find multiple points and a ceiling joist map can be created.

If the bar that holds up the ball chain partition is an extruded metal track then the mounting technique will likely not involve any brackets but instead involve drilling holes through the metal track at the correct points where screws can then be run up through the track into the support members in the ceiling.