| OSB SHEATHING SHRINKAGE CAUSING
STUCCO CRACKS ?
I got called to investigate a badly cracked
installation that appeared to have a very good Portland cement, lime
sand mix, was the right thickness, and was very durable and hard.
It was installed during the drought we experienced during last summer
fall by a very experienced and reputable stucco installation company.
general contractor is telling the stucco installer they must repair the
and recoat the project at the installer's
As a building envelope consultant,
to be fair to everyone involved and just deal with the conditions and
facts leading to those conditions.
After questioning the installer
mixing of components, the experience of the particular crew, the crew's
supervision, how much water was used in the application of the three
keeping the installation sufficiently moist during curing during a
and examining the construction, I observed the following
1. The upscale
a lumber package sent to the site and the wood framing and
roofing were in place within two weeks of delivery to the site.
2. The construction is
framing, 7/16" OSB sheathing and a Tyvek wrap, metal lath and the three
coat stucco installation with the finish coat applied in a skip-trowel
3. The stucco installer
the Tyvek installation appeared to be adequate with good over lap and
4. The stucco installer
the framer (the general contractor who is also the developer of the
installed the lath and nailed the lath approximately six to eight
on center to the OSB sheathing. The OSB used for shingle roof
has the proper spacing with metal spacer
but the wall sheathing boards contact each other, do have spacing and
not have separator clips or spacer clips. Boards have buckled or
moved out of the plane of the wall along horizontal board
5. There are more good
and door corners than ones with reentrant cracks off of the apex of
6. Multiple cracks in the
of the wall wood framing are evident out from windows and wall corners,
and especially on what is the second story.
7. There is at
one distinctive circular crack in the stucco installation and the
8. Cracks extend through
three coats and are much larger than hairline cracks in many places.
9. The stucco installer
there were cracks in the interior drywall installation but I was not
to observe these because the house had been recently recaulked and
10. A separate unattached
has numerous cracks in walls and also few cracks off of windows and
Two wall corners have bad cracks right in the corner.
Please share your thoughts with
of your comments in the FAQ section
made reference to your preference for OSB
plywood because you had fewer
cracks. This is somewhat surprising
the difference in the way OSB takes
on moisture and dries. Do you think
right in asking the general contractor to pay
for either the complete reworking of the
installation, or at least a preparation
coat and new flexible finish coat?
Thank you for your attention to this
to these requests.
In the last year and a half, I have
a method of keeping the cracks down to none
very few (two on one big house ,max) by
plasticizers in the finish coat. It costs
about 50 cents
a square foot more, so I just charge
I don't have to fight over
This may even be a solution if a recoat is
Typically, the worst cause of cracks
flimsy or inadequate braced
Not allowing enough time for the
brown coat to cure before the finish.
We generally let it sit a week, or
least 3 days. This creates a lot of
due to abnormal shrinkage. If someone
give me time, I simply turn down the
I also insist the roof is finished or at
loaded down before we start,
if it has a slate or Spanish tile
It sounds like probably that the framing
was way too green. If the walls have
badly out of plane this sounds most
like the culprit. It probably came straight
Or possibly abnormal expansion due to
If you can read the studs by the cracks,
is sounds like the reason. The
the inside shouldn't have cracks.
Usually, when plywood isn't
spaced, you can read the joints in the
I love OSB. I think OSB is better
it doesn't delaminate and warp like
And it doesn't bounce like a
when you shoot staple or drive nails in
It just seems to feel more solid. We
get fewer cracks. I think OSB tends
and plywood tends to shrink.
I think at this time you need to get the
pointing out of the way and concentrate
A flexible finish coat is your easiest
or painting with elastomeric paint, easier
It would be a solution for this
but I doubt these materials are
like the manufacturers say. Another down
is that you lose the natural portland
it will kill the cracks, and not use too
I don't think the plastering contractor was
but I feel he should meet the builder part
expense, particularly if he is an old or
or a real good payor. I would.
Maybe some lessons will be learned by
and everyone will still think positively
a dying tradition I am trying to
I hope all this helps. Write back if I
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