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Holding It Up
To ensure tight joints with wall and ceiling, crown molding
must be nailed into more than just drywall; at least 1"
of nail penetration into framing is needed. A stud sensor
will reveal where all the studs and joists are; however, you
will quickly discover that in the ceiling along two sides
(parallel to the joists) there will be no framing at all.
Before putting up drywall, 2 x 4 blocking can be installed
between the joists.
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undersized blocking. |
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However,
crown molding is most often an afterthought. After-the-fact
options include cutting holes in the drywall and laying wood
blocks in the ceiling (not good for the integrity of the vapor
barrier); climbing around in the attic (risk falling through)
and trying to glue the molding on using construction adhesive
(messy and limited effectiveness). The quickest and most effective way is to install lengths
of bevelled 3/4" plywood blocking around the room using
4" ardox nails or heavy screws driven into the top wall
plates. Deliberately undersize the blocking to avoid interfering
with the back side of the crown.
Which
Piece First?
Because outside corners are typically off square by 3° to 4°,
they can rarely be done straight from the miter saw. Being
a bit tricky, they're often recommended as the place to start.
This is almost always bad advice. Plan instead to finish on
the outside corners and this joint becomes easy to finesse
into a perfect gap-free miter.
Start
on the longest, most visible wall. If nothing else, make a
mistake here and the piece can still be reused on another
wall.
Inside Corners
Achieving perfect results for the more numerous inside
corners is the bigger problem. The advent of the power miter
saw has led to the practice of mitering both outside and inside
corners. But mitering both ends of a length of crown molding
requires an unachievable precision level in both measuring
and cutting. Additionally, the act of nailing crown molding
to the wall tends to open up inside miter joints, as will
any later stud shrinkage. The traditional cope joint should
always be used for inside corners.
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