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Painted stucco


Marc
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Yesterday's new construction had a paint finish over the cementitious stucco. The agent tipped me off that the reason for painting was that the original stucco color was an ugly yellow.

Question is this: Will this paint finish tend to retain incident moisture within the stucco and cause moisture issues later? If so, how do we get the paint off?

Marc

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Question is this: Will this paint finish tend to retain incident moisture within the stucco and cause moisture issues later?

Yes. Painted stucco is stupid. It's not a barrier finish, it's a water managed system.

If so, how do we get the paint off?

Marc

I am not aware of any way to remove paint from stucco that's not a total mess of chemicals and confusion.

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Yesterday's new construction had a paint finish over the cementitious stucco. The agent tipped me off that the reason for painting was that the original stucco color was an ugly yellow.

Question is this: Will this paint finish tend to retain incident moisture within the stucco and cause moisture issues later? If so, how do we get the paint off?

Marc

Yes, it can be a problem. Now if they used a paint that is designed for stucco it should be OK. My bet is that they used common exterior latex or acrylic based paint as it is cheaper than paint for stucco. Common paint changes the permeability of the stucco.

What can happen is that the paint can bubble and flake off the paint and the stucco with it. This comes from moisture trying to move to the outside from the interior of the wall system. Now, this may never happen but it is a common problem with painted stucco.

I do not know of a way that it can be removed without messing up the stucco.

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That's right. When contractors and homeowners improvise, and work against the known performance characteristics of a materials, the results are unpredictable.

Most of us like predictability. Them's that don't, probably aren't very good HI's.

I think it was Katen who coined a phrase that I use often; "Unconventional things tend to perform in unconventional ways"!

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Applying elastomeric coating creates a wall system that relies primarily on its surface-seal (i.e., the elastomeric coating) instead of its original concealed water resistive barrier (i.e., building paper and flashings under the cement plaster). To work, the surface-seal must block water at its surface, thereby preventing moisture from reaching the underlying, defective WRB and flashing elements. The primary advantage of a surface-seal for this project is lower initial cost and minimal disruption of residents. The disadvantages include:

• Requirement for frequent inspection and maintenance to minimize water intrusion. Ultimately, the life-cycle costs of elastomeric coating could approach or exceed the costs of returning the systems to their original design intent.

• The walls must be recoated every 7 to 10 years.

• Inability to collect and drain water that breaches the surface seal. The existing, underlying WRB and flashings would collect and drain most, but not all water that breaches the surface seals.

• Water that breaches the surface seal will dry more slowly since the coating will retard outward drying.

• Trapped moisture can cause the coating to blister and delaminate.

• Trapped moisture that is not collected and drained by the existing WRB and flashings can lead to microbial growth in the wall cavity.

• Silicones have the highest perm rating (i.e., allow more rapid outward drying) of available elastomeric coatings, but have a glossier finish and attract airborne dirt and pollution leading to streaking of the building surface.

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I've yet to see an elastomeric work on any building. There's alway bubbling, bleeding, and several outright disasters. Maybe they work, but you couldn't prove it by me.

The unstated message in Rocon's post is the only advantage is to the installer/developer/builder, with some consequential bleed off to the residents who are *not disturbed*, which could be rephrased as *uninformed and kept in the dark about future problems*.

There's no good argument for painted stucco.

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Using elastomeric paints over stucco is just plain idiotic; there is no other word to describe it. When stucco systems are specified, it's critical to focus on those details that will keep water out of the system. The system itself is water-resistant and is a drainage system.

One of the most important characteristics of stucco is its vapor permeability which allows moisture on the backside of the stucco to dry to the outside of the wall; if you coat stucco with an elastomeric finish and eliminate that characteristic of the system, you've essentially replaced the stucco with a piece of rubber and have turned a water management system that is able to dry to the exterior between rains into a petri dish. Now do you understand why using elastomeric paint (a fancy word for rubber or acrylic finishes that form a stretchable non-permeable membrane over stuff) can only be characterized as idiotic?

It's not necessary to paint stucco to keep it water resistant but stucco can be painted with paints that are designed for use with stucco and are vapor permeable. When properly mixed, applied and cured, 3-coat stucco has been proven by the Northwest Wall and Ceiling Bureau - authors of The Stucco Guide - to be vapor permeable but not water permeable. Stucco assemblies are consealed weather-barrier systems. The stucco accommodates moisture intrusion and the water resistant barrier behind the plaster is a drainage plane. Essentially, stucco is a rain screen.

NWCB set up a test to find out whether stucco was water resistant and whether a properly applied stucco application functions as a rain screen. Their test used three different stucco formulations on three different panels and they sprayed them each with over 100 gallons per hour for more than two hours. The idea was to create the equivalent of a rainstorm with near-40 mph winds. After two hours they examined the back of the plaster and found no moisture or dampness. Then they sprayed water into the top of an opening in a stucco wall to see whether the wall drained properly. The water drained all the way to the base of the wall and out at the weep screed and did not penetrate the WRB; because, when the stucco cured it caused the WRB to wrinkle and this essentially formed channels on the back of the stucco that allowed the water to drain cleanly to the base of the wall.

Now, to answer Marc's initial question he needs to know what kind of "paint" was used, because it might not have been paint at all - it might be a fog coat. Fog coating is a cementitious product used to change the color of stucco. It has to be applied in several light coats; but when done correctly will completely change the color, or even out existing color, and won't harm the system. Real paint on the other hand can damage the system because it doesn't bond to the stucco like fog coating and remain permeable - it forms a film over the surface. You can't simply strip it off with chemicals because doing so can damage the stucco. Probably the only way to get it off in order to fog coat it properly would be by blasting the wall with buckwheat hulls or something else that won't damage the stucco - not an easy process.

ONE TEAM - ONE FIGHT!!!

Mike

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Thanks Mike. This is not traditional stucco. It's cementitious but it's a one coat type of stucco that is applied over cement board with a plastic mesh embedded within it. I can only guess if and what kind of vapor barrier is installed behind the cement board.

The stucco finish looks funny to me, as if it were air entrained (spelling). I've seen many EIFS installations but not so many cementitious stucco jobs.

As to the write up.....the house is too young to have any visible damage yet and since it's possible a fog coat was used, it looks like I would be making a mistake to pull the alarm on this.

Marc

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Thanks Mike. This is not traditional stucco. It's cementitious but it's a one coat type of stucco that is applied over cement board with a plastic mesh embedded within it. I can only guess if and what kind of vapor barrier is installed behind the cement board.

The stucco finish looks funny to me, as if it were air entrained (spelling). I've seen many EIFS installations but not so many cementitious stucco jobs.

As to the write up.....the house is too young to have any visible damage yet and since it's possible a fog coat was used, it looks like I would be making a mistake to pull the alarm on this.

Marc

Sorta kinda like this?

http://www.nationalgypsum.com/literature/Stucco.pdf

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