We have always specified elastomeric coatings on renovation work for the crack bridging value, however lately some of our clients are insisting that we specify elastomeric on new stucco as well - Prof. Joseph Lstiburek - Mr. Mold himself seems to agree with this consensus, how about the members of this board. We typically specify 100%acrylic paint on new stucco. Comments would be appreciated.
Elastomeric coatings are usually acrylic-type products, applied at a fairly thick rate, perhaps 4 to 5 times the thickness of conventional paint coatings. The elastic property helps to hide small shrinkage/thermal cracks that can develop in stucco. They can be smooth or textured and normally include a mildewcide.
Stucco needs to cure at least 30 days, under ideal conditions. The substrate needs to be clean and dry to achieve a good bond. Some manufacturers require a prime coat as a barrier for highly alkaline substrates.
Jerome,
I am with Richard on this - I would consider a coating with elastomeric properties on new stucco because of the normal shrinkage cracks that can occur.
Some acrylics don’t have very good elastomeric properties, but many elastomeric coatings are acrylic based.
William
A couple of points re: “elastomeric coating” on stucco.
1 -
In Southern California (Southwest in general?) there is a lot of mix-and-match going on about “stucco” wall finishes. I’ve done projects where conventional portland cement plaster was applied over concrete unit masonry (Big Box type construction) with pilasters and other decorative treatment done with foam shapes and EIFS reinforced basecoat, followed by a top of coat of stucco finish (1/8" colored, fine aggregate portland cement plaster). That’s stucco over EIFS. I’ve done two-coat plaster base followed by textured acrylic finish (NOT elastomeric finish). That’s like an EIFS system without foam and acrylic basecoat. The plaster industry is ok with this. And then there are several one-coat plaster systems. See products by Omega Products and Parex.
2 -
The physics of plaster curing and shrinking (cracking) need to be considered. IF the plaster has not completely cured, it will continue to cure and shrink (crack) when it gets moisture, such as when rain soaks the plaster or when water runs down behind the finish as the building paper weather barrier does its job. When this additional shrinkage occurs or the building rocks-and-rolls during an earthquake (and that’s not just a California phenomenon), plaster will crack. When the cracking occurs, the crack will continue up through the acrylic (non-elastomeric) coating. It will also carry up through an elastomeric coating if the elongation property of the elastomeric coating is exceeded. Now, if the elastomeric coating is applied over the plaster base (especially “green” or not-fully cured or hydrated portland cement plaster), the likelihood of cracking of the coating is great. That’s because the percentage of elongation is infinite. Going from 0 to some crack width is infinite elongation. No elastomeric coating can fully accomodate this. The reason the crack may not be seen is that the coating is thick enough that that it splits at the contact surface but does not tear all the way up through the full thickness of the coating. Elastomeric coatings work well if the cracks have already occurred.
From an appearance viewpoint, acrylic finishes look better for a longer time EXCEPT when deeptone colors are used. These colors have organic pigments which fade quickly. I have one large shopping center project with vast areas of deeptone color that are repainted every 18 months because of fading.
I think the preferred choice, considering cost and longterm appearance, is to diligently moist cure a three-coat (conventional) plaster finish (scratch, brown and integral color stucco). Let the finish go through one winter season (to get good and wet to ensure that all the portland cement hydration is completed). Then, paint the plaster with an epoxy primer and high quality acrylic paint.
Second choice (for best appearance initially) is to do two-coat plaster base, moist cure the plaster and apply a high quality textured acrylic finish coat. Minimize cracking by providing proper control joints and expansion joints, as well as diligent moist curing. Restore the finish when needed, using acrylic paint (it doesn’t need to be thick like a textured acrylic coating).
Looks like John is on the ball..I second that application opinion and approach,
If you have elastomeric coatings near the ground or where they can be handled, they pick up more dirt, and are harder to clean (if anybody does it) than acrylics. Thus they may look pretty bad before there is need otherwise to recoat them.
Warning! Warning! Silconized elastomeric coatings attract dirt like a sponge. We currently are investigating an 18 story building in downtown Charlotte that was coated about two years ago and the dirt smuges when window washer do their work. The dirt is then embedded into the coating and is almost impossible to clean. This problem as been documented in other urban envirnoments as well.
Sorry to say that the national product manufacturer has been less than completely wonderful in dealing with this problem. Their lititure speaks to the product being “self-cleaning” which is not the case.
The problem is not limited to just near the ground. The entire building is dirty. Jo is correct in her evaluation. Careful consideration should be given to envirnomential conditions before specifing this product.
Hmmm. How can you tell when a building product rep is not being completely truthful? When they speak about the merits of their product, their lips move.