|
Why Stucco Cracks
And when it does, don't ignore it
by Broderick Perkins
Cracking stucco is a sticky subject. Some experts say cracks are
normal. Others insist cracks occur only when installation is
faulty. They all agree, however, that ignoring them can be
costly.
BEFORE: Stucco cracks filled and ready to redo. Photo
courtesy of Elastek.
"It's like field surgery," said Christopher Alba, an architect
and builder with Santa Fe, New Mexico-based Environetics.org, a
building forensics firm. "The worst thing you can do is allow
the crack to continue to open. The first thing someone should do
when they see a significant crack is to seal it with a silicon
sealant."
To stop cracks, however, you must first determine why they
appear.
Stucco is cement plaster, a mixture of cement and aggregate
(sand) and other approved materials that is used as wall and
ceiling coverings, most often in the South and Southwest. It is
applied directly to masonry or concrete walls or over a metal
lath, a wiry substructure that is secured over construction
paper and attached to frame construction, masonry, or concrete.
Building codes say stucco should be applied in three coats
forming a 7/8-inch total thickness. Each layer must be cured
before the next layer can be applied.
There are two categories of cracks, internal and external, says
Bob Carroll, a forensic architect with BuildingAnalysts.com in
San Jose, California. As it loses water, stucco is prone to
internal stress cracks.
"Stucco is hydrated. The loss of the water during the curing
process causes some internal stress so you get shrinkage cracks.
It's normal, but not necessarily acceptable," Carroll said.
External stress includes the effects of seismic activity,
settlement, temperature changes and moisture. And shoddy
workmanship increasingly compounds the effects of both types of
stress.
AFTER: A new and long-lasting surface. Photo courtesy of
Elastek.
"Cracks are 'normal' because the industry has deteriorated to
the point where it is normal," Alba says. ``A lot of it is the
lack of care taken during installation. You can install stucco
that performs extremely well and doesn't crack." Cracks will
"tell" you what went wrong during construction.
A vertical and horizontal grid of cracks imply an improperly
attached lath that increases internal stress. "People will try
to use a coating on top of it, but it's potentially one problem
on top of another," Alba said. ``To be honest, there's not a
good fix except for re-stuccoing."
Likewise, a spider webbing pattern of cracks indicates
insufficient curing. The stucco is too thin or was installed at
the wrong temperature. "If water dries out too fast, you get an
abnormal amount of shrinkage cracks," said Carroll.
Cracks near corners of a building often indicate that the lath
was pulled too tight, causing a thinner application of stucco in
that area. "If it's too thin, the water gets behind it and it
just explodes," says Alba.
Diagonal cracks often speak of deeper problems related to
seismic activity, structural problems or both. A diagonal crack
could represent a shifting foundation, settling or, if it occurs
around windows or doors, improperly framed openings.
Materials used in today's construction also create undo external
stress on stucco. "Twenty-five years ago, you got a board that
was straight," says Alba. ``Today you get something that is
almost green and it changes (dries) for up to two years. That
puts out a load of stress. Nails pop if a panel twists. It can
break stucco."
The forensic experts say if the home is relatively new or under
warranty, you should press the builder for repairs. Check your
state's building codes for laws that protect you for much longer
than a builder's typical one-year warranty. For older homes,
numerous or persistent cracks or crevices of 1/16 of an inch or
more warrant an inspection.
"Call someone who is not selling stucco, but is familiar with
it," Alba says. ``A design professional, builder, architect or
structural engineer."
|
