We just finished a 6" MDF crown job. We coped all the inside corners because a cope (butt joint) is much stronger than a miter, and this condo is 41 floors up, so the building is going to sway. There was one 22.5 inside corner which we did miter, and it's the best inside joint! One of my guys thinks MDF can't be coped because when you spring the cope into place, it wants to crumble. So he thinks all the inside corners should be 45's. Tell me he's nuts!
(Architectural Woodworking Forum)
From contributor B:
I coped 6" crown on a recent job and it looks great. After researching crown installation conversations here, I found it is about 50/50 on cope/miter. What did you use for a backing in areas without joists to nail to in the ceiling?
Comment from contributor J:
I coped 6" crown MDF moulding on 8 condo's in a 10 story building a couple of years ago. The ceilings were concrete and the walls had metal studs. I didn't use any blocking, just shot through the drywall into the studs. I used tubes of Lapages no-nails glue in a caulking gun to glue the top edge of the crown, pushed up tight to the ceiling, wiped off the excess glue and it made an excellent joint. If the ceiling was uneven in places I would hold the crown with a Tapcon screw for around ½ an hour, then remove it and fill the hole. I was back to this building recently, and none of these crowns have moved - not even a small seam.