Backer is a real good idea on an old house. Finding the studs is not a
problem. The waves and bows of the ceiling and walls make installation
difficult. With the backers you can strengthen everything out better. Yes
put a profile on the backer but if your walls are really bowed put up the
backer with out a profile and install a smaller trim piece under it. This
will help hide any irregularities.

wrote in message
ups.com...
the previous owner of my circa 1900's home put a narrow cove crown
moulding up after he redrywalled the ceiling. that moulding is removed
and i am about to put up wide crown moulding. is a top and bottom
backer board advisable to eliminate the issues around stud finding? or
is it not worth the hassle? if so are the top / bottom backer boards
extended beyond the moulding edges? if they extend should i run the
exposed backer boards through my router to give it a profile? any
comments would be helpful - although i'm a handy fellow i've never
attempted costly crown moulding installs.

ty