Why Paints Fail

January was a very busy time for me as I spent valuable time at two premier Contractor events in North America – The PACE National Convention in LA, and the CertaPro National meeting in Tucson. I engaged numerous contractors in discussions about their favorite paints and favorite paint jobs. There was genuine interest in proper paint selection and in understanding how to avoid premature failures. Hence this month’s newsletter looks at some factors that influence paint failure:

a. Film Thickness and Uniform Coverage: Thicker films are desirable for some obvious reasons. Since coatings provide barrier properties, then one can envision that thicker films would help prevent moisture, UV and other harmful elements from getting to the surface. In the case of bare wood and masonry, thicker films can better absorb changes in the surface, while thin film coatings would tend to crack as the substrate moves. Thicker films generally provide for better hiding and stain blocking, as well as better mildew and corrosion resistance. Non-uniform paint coverage (resulting in peaks and valleys) can enable dirt build up on the coating.

b. Substrate Effects: The type and condition of the surface to be painted, significantly influences the paint selection. The market place has evolved to offer products engineered for specific substrates. Most manufacturers today offer products that are uniquely suited for wood and masonry applications. With aged and weathered substrates, proper surface preparation becomes critical to avoid premature failure. It is extremely important to paint on a surface with no loose or foreign particles. Appropriate techniques, for example power washing, must be employed to remove those loose particulates from the surface. We strongly recommend the use of an appropriate primer as well.

c. Impact of Priming: The use of the proper primer is essential to ensure that the paint finish delivers acceptable performance over the lifetime of the paint. Priming needs will vary depending on the substrate and conditions under which paint is applied and will be dealt with in more detail next month. For this newsletter, we focus on the role of priming in enabling adhesion and providing a uniform appearance. Primers are especially important when painting over aged or chalky surfaces. Quality primers, based on 100% acrylic binders, provide good adhesion and result in longer durability of the topcoat. Testing done at the Paint Quality Institute shows a clear trend with primer plus 2-topcoats out-performing primer with single topcoat.

The panels below show that even one coat of topcoat over a primer outperforms two coats of topcoat direct to the weathered wood.

d. Cold Temperature Applications: The emulsion used in waterbased paints consists primarily of spherical particles dispersed in water. In a fully formulated paint these emulsion particles are mixed with pigment and other additives. After the paint is applied and it begins to dry, the pigment and binder particles come closer and closer together, until ultimately, the binder particles fuse and bind the particles into a tough, “continuous” film. Painting under adverse conditions can impact this film formation process and result in premature cracking and flaking. Before painting under stressed (e.g. low temperature) conditions we suggest you review the manufacturer’s recommendations. More recently paints have been introduced that allow for painting as low as 35° F – prudent manufacturer’s guidelines must still be followed to avoid pitfalls during these low temperature applications.

Product choice (and more importantly ingredient choice) remains the other key component in ensuring a quality paint job. To assist you further with proper product selection for a given job we encourage you to review our step-by-step guidelines at http://www.paintquality.com/contractor/ppp/index.html.