Exterior Paint Solution Center

Paint Incompatibility

• Use of water-based latex paint over more than three or four coats of old alkyd or oil-based paint may cause the old paint to ‘lift off’ down to the substrate.

• Remove all loose and peeling paint, scrape, prime and repaint using another coat of compatible alkyd or oil-based paint. The other option is to completely remove all the old existing paint, prepare the surface by cleaning and sanding, then prime before top coating with a high quality latex exterior primer and paint.

Peeling

• Excessive moisture in the substrate.
• Seepage of moisture through uncaulked joints, worn caulk, or leaks in roof or walls.
• Use of low quality paint.
• Applying an oil-based paint over a wet surface.
• Earlier blistering of paint (see Blistering).

• Try to identify and eliminate cause of moisture (see Efflorescence/Mottling). Prepare surface by removing all loose paint with scraper or wire brush, sand rough surfaces. Apply an exterior primer to all bare wood surfaces. Repaint with a high quality latex exterior paint for best adhesion and blister resistance.

Poor Alkali Resistance

• A coating that was applied to new masonry before it had a chance to cure at least 30 days at 700F. Fresh masonry is likely to contain lime minerals, which are highly alkaline. Unless the lime has a chance to neutralize, its alkalinity will actually “burn’ the paint off the surface causing loss of adhesion.

• Prior to painting, allow masonry surfaces to cure for at least 30 days at 700F.  If this is not possible, the painter should apply a quality, alkali-resistant sealer or latex primer, followed by a high quality latex exterior paint.

Poor Galvanized Metal Adhesion

• Improper surface preparation, such as inadequate rust removal.
• Failure to sand baked-on enamel finishes or glossy surfaces before repainting.
• Failure to apply a latex-based primer before applying an oil-based or latex-based paint.

• Any white rust on galvanized metal should be removed with a wire brush and wiped clean with mineral spirits. Apply a latex based corrosion-resistant primer. New or previously painted galvanized metal that is completely rust-free can be painted with a top quality latex paint without applying a primer; however, a metal primer should always be applied to unpainted galvanized metal before applying an oil-based or alkyd based topcoat.

Poor Gloss Retention

• Use of an interior paint on an exterior application.
• Use of a low quality paint.
• Use of a gloss alkyd or oil-based paint in severe sunlight exposures.

• Severe sun exposure can degrade the binder and pigment of a paint, causing it to chalk and lose its gloss. While all types of paint will lose some gloss over time, lower quality paints will generally lose gloss more quickly. The binder used in high quality latex paint is especially resistant to UV radiation, whereas oil and alkyd binders actually absorb the radiation, causing the binders to break down. Surface preparation for a coating showing poor gloss retention should be similar to that used in chalking surfaces (see Chalking).

Surfactant Leaching

• Mist, dew or other moisture drying on the painted surface shortly after it has dried.
• Painting in cool, humid conditions or when rain is imminent. The prolonged drying time allows the surfactant in the paint to leach out and rise to the surface before paint thoroughly dries.
• Dark colors made with large quantities of colorant are more susceptible.

• Avoid painting in the late afternoon if cool, damp conditions are expected in the evening or overnight. If the problem occurs in the first day or so after the paint is applied, the water-soluble surfactant can sometimes be rinsed away. Fortunately, even stubborn cases will generally weather off in a month or so. Surfactant leaching should not affect the ultimate durability of the coating.