Painting Stucco

Stucco, concrete block, and other masonry have the reputation for being strong materials but the downside is that they're also brittle and tend to develop cracks as they expand and contract with changes in temperature. In wet climates like in Florida and along the Gulf coast, small cracks can quickly lead to big problems--rot, mildew, and mold--because they allow wind-driven rain into the wall. In colder, northern climates where there are freeze/thaw cycles, if water enters the cracks and turns to ice, small cracks soon turn into big ones. 

If you've got a stucco or masonry house, the answer is to use an elastomeric paint. These heavy-duty acrylic house paints are higher in volume solids, which allows them to be applied with a greater film thickness, giving them maximum flexibility and the ability to stretch and bridge small cracks and minor gaps. Typical acrylic paints might have a 1.5 mil dry film thickness, compared to an 8 mil dry film thickness for Benjamin Moore's Moorlastic low-lustre elastomeric paint, for example. Although much thicker, elastomerics have about the same 10-15 years service life as regular acrylic paints, because the pigments and resins used in still break down when exposed to sunlight. 

Elastomeric paints are water repellant, but the good ones are also vapor permeable, so that wall assemblies that get wet can dry out; otherwise, blisters can develop under the coating from trapped water vapor. The vapor permeance--or 'perm rating' of elastomeric coatings can vary widely--Benjamin Moore's Moorlastic 100% acrylic elastomeric coatings have a perm rating of 3.4, for example, slightly less than a typical acrylic house paint. 

Prep work. As with any coating, prepping the surface properly is the key to a lasting finish. Elastomeric paints are stretchy, but they can't bridge wide cracks. After pressure-washing to remove dirt, chalkiness, and loose paint from the substrate, perform a simple credit card check: if the edge of a credit card will fit into a crack, it must be repaired with either a knife grade or brush grade patching compound, though it can be tricky to get a good patch that won't show through even a thick elastomeric finish. 

Before painting both new and previously painted surfaces, use a primer/sealer. The sealer helps reduce the porosity of masonry surfaces and improve adhesion, and provides added protection against the extreme alkalinity of new masonry. On previously painted surfaces, the primer/sealer also binds up residual pigments that aren't removed by washing.

Application. Elastomeric paints are very thick, so they don't spray easily, but spraying and backrolling is the method that most pros use to get the thick film thickness required for these paints. Rolling and brushing may require multiple coats to build up to the recommended film thickness. 

Elastomeric paints cost about the same per gallon as standard acrylic paints, but offer only about a quarter of the coverage, so are more expensive to use. Colors are limited too, since most elastomerics only have a white base. It's easy to paint masonry a darker color, though: just coat with an elastomeric, then topcoat with a tinted standard acrylic paint (don't topcoat with an alkyd paint).  

Comments

[Auto paint colors]

If you are preparing to paint your car or simply considering the option the first thing you need to know about Auto paint colors is that not all colors work for all cars. If you think about cars that has been driving around town, you can probably think of some very different cars that made him think that what they were thinking about painting the car that color.

[Benjamin Moore]

Hi Claudia,

Benjamin Moore does not recommend using exterior products for interior use. One reasons is that mildewcides used in exterior products release a strong odor from the exterior alkyd resins incorporated in the formula. This is acceptable for exterior use but in the confines of an interior, this would not be suitable. Please consider using a Benjamin Moore interior product instead. Interior stucco may be painted with any conventional latex/acrylic interior paint coating.

[Claudia Macora]

Is the Moorlastic 100% acrylic paint used for the inside of the house as well? Or, is this just for the outside? I need to paint my interior walls, which are stucco and was wondering if this is the option to go. Thank you.