Here are some suggestions that might make the job easier for you.
Materials: You can get crown molding in a
variety of materials: For paint grade, finger
joint pine and MDF are two I see the most, and both are usually available
pre-primed. I don't like MDF molding generally, but it works fine for crown molding.
The reason I say that is MDF tends to blossom when you nail it and it is
not very stong, but that is not too important up at the ceiling. You can also get
plastic crown molding but be sure it is paintable. What I have seen is shorter
lengths which would require splicing, but the plastic material is harder to splice and
to glue and harder to nail.
To install anything but the smallest crown,
you will need a power miterbox or compound miter saw; it is not necessary
to have a sliding compound mitersaw. If you don't have a suitable saw, you can
probably rent one.
Measuring: To measure for the length of each
piece, measure at the ceiling from one direction to a convenient point (say 70")
and put a mark on the wall. Then measure from the other direction and add the two
figures. Look at the end of a piece of the stock with a square to figure out how far
out it comes on the ceiling and how far down on the wall. The molding is seldom
set at 45 degrees; a more common situation might be 2" out on the ceiling and
3" down the wall. Put several marks on the wall for that dimension; maybe one
near each end and one in the middle. Cut the longer pieces first; if you cut
wrong, you can then use that piece for a shorter one.
Cutting: Cut the molding upsidedown on
the saw, what some people call "cutting in position". Yes, the compound mitersaw
will cut it flat, but I don't recommend doing that since it is hard to figure out
the settings and even harder to visualize so you don't cut wrong. So put a couple
pieces of masking tape on the saw bed and mark the ceiling dimension on it from the back fence.
Or you can fasten stop blocks on the saw bed. Make sure you have some outboard
support for the material so it rests square on the saw bed. Now set the piece
upside down on the saw and visualize it as being on the ceiling so you
cut the angle correctly. Remember that for an inside corner, the point on the
piece will be on the wall side; for an outside corner, the point will be on the
ceiling side. For crown around a bullnose drywall corner, you should cut a small corner
piece to miter between the other two pieces; it will be 3/4" to 7/8" wide
at the wall. Obviously the angles you are working with here are 22-1/2
degrees for a nominal 90 degree outside corner.
Coping:You can cope inside corners
if you wish, but it is extra work that is not cost-effective unless you are working
with a natural wood finish. Also, it does not work well with MDF molding because
it doesn't cope cleanly. But to cope the corner, cut the 45 degree angle and then with
a coping saw, back cut the material away. This leaves you with a shaped end that will
connect nicely to the next piece around the corner. Not easy to make this coping cut
cleanly, and that is why I don't bother.
Splicing:If you have to splice a piece,
it is best to do this before you install it. Use a piece of 1/8" or 1/4" ply for a backer
piece and glue it; it will have to dry some before you heft it into place. For a
bullnose corner, it would be best to glue the small corner piece to one of the longer
pieces before you put it in position. You can hold it in place with masking tape
until the glue cures. There is a fast set, high tack glue by Titebond that
will speed this process.
Installing:To install each piece, set
several nails in the wall maybe an inch below where the molding will go. These will
support the piece as you move it into position. Then push it up so it lines up with
the mark on the wall and nail it with finishing nails. For 3-1/2" molding you can nail
near the center with 8p nails into the double top plate of the framing. If that
doesn't work for you, find the studs and nail near the bottom into the studs.
If it is necessary to nail the top edge also, nail into ceiling joists or cross
nail into the drywall every couple feet. If you are working with steel studs,
you will have to use trim screws instead of finishing nails. These are slender
screws with a very small head. It would be best to predrill holes for the screws
so you don't split the crown. Fitting the corners together
may be easier if you have a scrap piece cut at the angle to push against the piece
you are nailing. It is best to not nail within about 2' of the corner each direction
until you get both pieces in place so you can adjust them to line up. Use a soft
block of wood and a hammer, if necessary, at the ceiling or wall to move the crown
either up or down to line up the pieces.
Caulking:Caulk both edges of the crown
molding to wall and ceiling to cover any gaps and give a neater job. Also caulk any
gaps in the miters. As you are doing this, fill the holes in the wall made when you set the
support nails and the nail holes in the molding. I use white latex caulk for this.