Ask the pros- July, 2001
By Reggie Bullard





I got called to investigate a badly cracked stucco installation that appeared to have a very good Portland cement, lime and sand mix, was the right thickness, and was very durable and hard.  It was installed during the drought we experienced during last summer and fall by a very experienced and reputable stucco installation company. The general contractor is telling the stucco installer they must repair the installation 
and recoat the project at the installer's expense.

 As a building envelope consultant, I want to be fair to everyone involved and just deal with the conditions and the facts leading to those conditions.

After questioning the installer concerning the mixing of components, the experience of the particular crew, the crew's supervision, how much water was used in the application of the three coats, keeping the installation sufficiently moist during curing during a drought, and examining the construction, I observed the following 

1.    The upscale residence had a lumber package sent to the site and the wood framing  and completed roofing were in place within two weeks of delivery to the site.
2.    The construction is wood 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 pattern.
3.    The stucco installer said the Tyvek installation appeared to be adequate with good over lap and good coverage.
4.    The stucco installer said the framer (the general contractor who is also the developer of the subdivision) installed the lath and nailed the lath approximately six to eight inches on center to the OSB sheathing.  The OSB used for shingle roof decking 
has the proper spacing with metal spacer clips but the wall sheathing boards contact each other, do have spacing and do 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 window and door corners than ones with reentrant cracks off of the apex of those corners.
6.    Multiple cracks in the pattern 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 least one distinctive circular crack in the stucco installation and the stucco is hard.
8.    Cracks extend through all three coats and are much larger than hairline cracks in many places.
9.    The stucco installer stated there were cracks in the interior drywall installation but I was not able to observe these because the house had been recently recaulked and repainted.
10.    A separate unattached garage has numerous cracks in walls and also few cracks off of windows and doors.  Two wall corners have bad cracks right in the corner.

Please share your thoughts with me.  One of your comments in the FAQ section 
made reference to your preference for OSB over plywood because you had fewer 
cracks.  This is somewhat surprising considering the difference in the way OSB takes 
on moisture and dries.  Do you think I'm right in asking the general contractor to pay 
for either the complete reworking of the stucco installation, or at least a preparation 
coat and new flexible finish coat?

Thank you for your attention to this e-mail and to these requests.
In the last year and a half, I have discovered 
a method of keeping the cracks down to none or very 
very few (two on one big house ,max) by adding 
plasticizers in the finish coat. It costs me about 50 cents 
a square foot more, so I just charge more. 

 I don't  have to fight over cracks anymore. 
This may even be a solution if a recoat is done. 

Typically, the worst cause of cracks are: 

flimsy or inadequate braced framing. 

Not allowing enough time for the 
brown coat to cure before the finish. 

We generally let it sit a week, or at 
least 3 days. This creates a lot of cracks 
due to abnormal shrinkage. If someone won't 
give me time, I simply turn down the job. 

I also insist the roof is finished or at least 
loaded down before we start, Particularly 
if it has a slate or Spanish tile roof. 

It sounds like probably that the framing lumber 
was way too green. If the walls have shifted 
badly out of plane this sounds most likely 
like the culprit. It probably came straight from 
the sawmill. 
Or possibly abnormal expansion due to the 
dry/wet season. 
If you can read the studs by the cracks, this 
is sounds like  the reason. The drywall on 
the inside shouldn't have cracks. 

Usually, when plywood isn't adequately 
spaced, you can read the joints in the plywood, 
(or OSB). 
I love OSB.  I think OSB is better because 
it doesn't delaminate and warp like plywood. 
And it doesn't bounce like a basketball 
when you shoot staple or drive nails in it. 
It just seems to feel more solid. We do 
get fewer cracks. I think OSB  tends to expand, 
and plywood tends to shrink. 

I think at this time you need to get the finger 
pointing out of the way and concentrate on 
constructive solutions. 
A flexible finish coat is your easiest ticket out, 
or painting with elastomeric paint, easier yet. 
It would be a solution for this project, 
but I doubt these materials are breathable 
like the manufacturers say. Another down side 
is that you lose the natural portland cement color, but 
it will kill the cracks, and not use too much thickness. 
I don't think the plastering contractor was at fault, 
but I feel he should meet the builder part way on the 
expense, particularly if he is an old or repeat customer, 
or a real good payor. I would. 

Maybe some lessons will be learned by all here, 
and everyone will still think positively about stucco, 
a dying tradition I am trying to preserve. 

I hope all this helps. Write back if I can 

Thanks for visiting my site

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