There are some guidelines to consider when painting new stucco i.e. cure time, priming, filling cracks, and painting.
Stucco is a popular building material used for residential exterior siding. Stucco is a cementitious material that typically consists of sand, Portland cement, lime, and water and in some cases it may contain additional additives. When applied to wood framing, stucco is usually attached to wire lath which in turn is attached to the structural framing. Wood framing must be protected by a water resistant moisture barrier such as asphalt building paper or other types of engineered building wraps, before the wire lath and stucco are applied. Stucco can also be applied directly over properly prepared masonry surfaces such as brick, block, and concrete.
Cure Time for New Stucco
If possible, new stucco should be allowed to cure for thirty days before primer and paint topcoats are applied. Painting un-cured stucco can result in paint failure. White powdery deposits from minerals and soluble salts also known as efflorescence is a common problem. As trapped moisture migrates toward the stucco surface, it carries these mineral deposits with it. This can cause paint discoloration and in some cases adhesion problems. High alkalinity (pH greater than 11) associated with un-cured stucco can also cause paint burn. An adequate cure time will help to eliminate these problems. If new stucco must be painted before it has completely cured, it is best to use an alkali resistant masonry primer/conditioner.
New stucco usually develops some cracks during the curing process. As the water is eliminated and the stucco hardens, hairline cracks less than 1/16 inch tend to occur. Applying the primer and paint coats with a paint roller will typically fill these narrow cracks. The roller action helps to push the paint into the cracks. Paint application with an airless sprayer alone will not effectively address hairline cracks.
Stucco cracks with a width greater than 1/16 inch generally require a stucco patch type filler to bridge the gap. Brush-able elastomeric filler works well for cracks up to a width of 1/8 inch. This type of stucco patch should only be applied after the new stucco has already been painted with a coat of primer. Brush the elastomeric filler directly onto the cracks. It is very important to feather the edges of the filler lines with the brush. Failure to do so will allow the filler lines to remain visible after the topcoats of paint have been applied.
Thicker grade elastomeric filler can be used to fill stucco cracks greater than 1/8 inch. It is available in cartridges where it can be applied with a caulking gun or standard containers where it can be applied with a flexible putty knife. It is important to feather the edges of the filler lines as is the case with the brush-able elastomeric filler. The thicker stucco patch fillers should also only be applied after the stucco has been properly primed.
Painting New Stucco
Painting new stucco should include a primer coat and one or two finish coats. Two finish coats are often preferable for many stucco textures. Be sure to use a primer and paint that is compatible with an exterior masonry surface.
Painting new stucco with a paint brush and roller does a far better job to fill all the stucco pores than does spray painting with an airless sprayer. A 1 to 1-1/2 inch lambskin or lambskin/synthetic combination roller cover is well suited for most stucco textures. A 3 or 3-1/2 inch paint brush with synthetic filaments (bristles) is a good choice for cutting in the paint. A combination nylon/polyester brush works well for this application.
Spray painting immediately followed by a paint roller, also known as back rolling is another effective way to paint stucco. This is more easily accomplished with two people working together. It is important to closely follow with the roller before the paint has a chance to set up. As is the case with spray painting, this method requires all the necessary masking and covering.