I am hanging some 5 1/4" UMDF Crown w a 45 degree spring angle on a 9" wall with a 2 1/2" 15 gauge. The ceiling joists run parallel to the walls running one direction and the ceiling plate seems to stop about an inch short of the end of the ceiling run of the crown. Per an old post by KCTermite I cut some blocks out of scrap 3/4" plywood I had on hand and toe nailed them into the wall joists and ceiling plate (the thing for drywallers).
I tried nailing them through the middle into the joist and they tended to split. Termite's instructions were to toenail, perhaps for that reason.
My question is where to nail and at what angle. I am thinking horizontally throught the foot of the crown (which is what I call the part running against the wall) and then hitting the plywood block with a coupe of nails angled from the right and left into the sides of the triangular block.
Here is a pic of the way I set it up. The blue tape marks the location of ceiling joists and wall studs.
Am I doing this allright and after all corners are adjusted, how close to the end should the boards be nailed with a 15? Should I hold off nailing close to the ends until I have access to an 18 gauge brad gun? I am coping. Is there any point in trying to glue the corner joints? Thanks.
IMHO, 18 ga is too light, 16ga is OK, but I prefer 15 ga. But nails tend to pucker in MDF, and bigger nails pucker more. I prefer wood. You can nail into wall studs all around but only into ceiling joists on two walls. On the other two walls use the blocks. gluing joints not needed for painted trim, caulk does the job. Always cope inside miters.
Thanks Bill. Not sure about what you mean by nails puckering in MDF. I think you mean the mdf raises around where the nail enters. This stuff only does that on the back side where the nail exits. I don't know if there is a difference between Ultralight MDF and MDF as far as the pucker factor. I was only considering using an 18 gauge for nailing near the corners. Everything else is 2 1/2" 15 gauge.