responds: On any stucco job, you have to
expect both the scratch coat and the brown coats to
have minor cracking from shrinking.
Excessive cracking, however, usually means
something was done improperly — for
example, the mix may have been "too rich" (too much
cement), the stucco layers may have been too thick,
or the walls may not have been allowed to cure
A "too rich" mix almost always results in
cracking, especially when the coat is applied too
thick. Normally, the scratch coat should just cover
the wire. The next layer (the brown coat)
may be applied the same day, providing the
scratch coat has had adequate time to set up.
Ideally, both surfaces should be "misted" after
they’ve been allowed to set awhile. This
will slow their curing and maximize the strength of
each coat. It’s especially important to
"damp cure" the walls on very hot and windy days.
If either coat flash-cures, it will be weak.
Finish coat. Ideally,
you should allow a week to pass before finishing
the stucco. This permits complete curing of both
the scratch and brown coats. The finish coat (about
1/8 inch thick) is applied over the previous two
coats (totaling about 3/8 inch), so any hairline
cracks are now covered. Nevertheless, stucco is a
cementitious material, so it is very unforgiving.
Even if there are no cracks at all in the scratch
and brown coats when the finish is applied, you
will undoubtedly find some cracking several months
later due to expansions and contractions of the
framing, movement caused by wind loads, and, of
course, any seismic activity.
As for lath, here in central Ohio,
we’ve had good results with 1-inch,
18-gauge keymesh wire lath, otherwise known as
self-furring metal lath or stucco netting. For
overhangs, we use expanded metal lath (sometimes
with paper backing) because it’s easier to
handle when working overhead.
Steve Thomas has worked the stucco trade in
Columbus, Ohio, for seven years.