MDF Crown in a High-Rise

Steel stud walls and a cement ceiling add a few wrinkles to what would otherwise be a routine crown-molding install. June 23, 2006

Question
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!

Forum Responses
(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?

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From the original questioner:
The ceiling was cement, so we used blocks everywhere. We ripped a 2x4 @ 45@ so we could use both halves. To install, we designed the blocks to sit 1" below the ceiling, (3/4" and 1/4" plywood nailed together pushed up to the ceiling, with the block under that. This was enough clearance for a screw gun without scratching the ceiling). We used Liquid Nails and 1 screw to attach to metal studs. I left 1/8" space between the block and the spring angle of the crown, but next time I'd leave closer to 1/4". The Liquid Nails pushed the block away from the wall, and with 1 screw, they wanted to twist.

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The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

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.