Okay, I am picking up some crown today, just enough for the dining rook which is a simple 12"X10" rectangle. I haven't decided on a profile, but it will likely be 5-1/2" mdf. Walls are 9" tall. I read a good discussioin on how to make backers here. My question is when a backer or whatever (nailing block or strip) is needed or a good idea. I guess it depends on if you have wood above the ceiling top plate, such as a drywall nailer, or if you want to cross nail. My feeling is to avoid making more holes than necessary, and cross nailing doubles the number of holes. I will be using 2-1/2 inch 15 ga. nials..
Here is an existing thread talking about how to make a nailer, but I am not clear on when one is needed. Assume I have a sheetrock nailer over the ceiling top plate. (I can stick my head up in the attic of this two story and see if there is a sheet rock nailier for the ceilng of that floor. I am guessing, but flying blindly that the bottom plate of the second story wall would rest on the top plate of the 1st story and that would give me plenty of wood to hit. I think I may have this wrong, as the top of the spring moves away from the plane of the wall plates, bottom or top, as taller molding is used. Does a drywall nailer extend out a few inches above the ceiling drywall? I can easily cut an inspectioin hole in the ceiling drywall that won't be noticeable onece as the crown will cover my not too artful repair.