Hanging curtains on a hard plaster (plaster and lathe) wall can be difficult. Traditional mollys or wall anchors will often pull out of the plaster and leave large holes that require repairs. First, it is important to know the weight that will be applied to the curtain rod. For large and heavy draperies, the best option may be to hire a professional hanger. For average weight curtains, standard toggle bolts will usually work.
Locate any near the window using a stud finder. Mark the locations with the pencil and use a tape measure to see if the stud locations will work when hanging the curtain. The best installation of curtain brackets is directly into a stud. Usually, studs are located within the first 2 to 3 inches from the edges of a window. If you mount your curtains above the window trim, you can probably mount the curtain brackets to studs on either side of the window.
Measure and mark the location where the curtain brackets are to be mounted (if you don't find any studs).
Drill a hole of the same diameter as the toggle bolt (at its widest point with the wings folded). Drill through the lathe and plaster.
Assemble the toggle bolt by sliding the machine screw through the curtain bracket and then thread the butterfly wings onto the end of the screw so they fold up toward the head of the screw. Insert the toggle bolt wings into the wall first, making sure the wings go all the way through to the other side of the lathe. The wings will spring open inside the wall cavity, blocking them from coming back through the hole.
Tighten the toggle screw to the bracket and wall. Often it is necessary to assemble two toggles on one bracket before installing. The diameter of the machine screw determines how much weight the toggle can hold so check the weight chart at the store when you purchase the toggle.
Do not buy plastic toggle bolts. Take the curtain hardware to the store with you when you buy the toggle. Have a good idea what the curtain weight will be. You can determine this by holding the curtains in your arms and stepping on your household scale. Then simply subtract your weight without the curtains. Knowing the weight of the curtains will help you buy the correct toggle for your application.