COATING PERFORMANCE

Semi- penetrating stains These products are almost exclusively alkyd/ oil based to achieve maximum penetration into the wood. Latex products do not penetrate as well. Because there is very little surface film to resist sun-light and moisture, the lifespan of these products is relatively short. However, a reasonably transparent appearance may be maintained, and the lifespan lengthened considerably if two coats are applied together, e.g., apply the second coat while the first coat is still wet. This will effectively double the lifespan before recoating is required, and is particularly effective on roughhewn or weathered siding. One coat of semi-penetrating stain on smooth siding will usually have to be recoated in two to three years. The second coat will last considerably longer, however. The two coat application method on roughhewn or weathered wood may last up to six years depending on the degree of exposure. On horizontal surfaces, such as decks, one coat is recommended. The life span is further shortened by abrasion from foot traffic. However, recoating and the blending in of worn areas is usually not too difficult. If the wood is weathered somewhat to reduce the mill glaze and increase porosity, one coat of stain will last longer owing to deeper penetration. 

Heavy bodied and solid color stains These products are available in alkyd/oil and latex types. They are classified as continuous film coatings since they resemble a paint film although they are somewhat thinner. Because they produce more surface film than semi-penetrating stains, they have more resistance to sunlight and weather and have a longer lifespan. Acrylic latex stains have better color retention than alkyd/ oil stains (are less apt to fade) and to have a somewhat longer Iife span. While they obscure the grain pattern of the wood, they allow the surface texture to remain, and both are extremely popular finishes for roughhewn siding. Neither product fares very well over smooth, flat grain surfaces, however.

Exposure The most severe exposure to sunlight and moisture (rain, snow and dew) are usually the south and west sides of a structure. Over-hangs, shade trees and porch enclosures will lessen exposure, and somewhat protected areas will not have to be recoated as frequently. If, in the case of paint, it is not practical to apply two topcoats at the onset to the entire structure, two coats may be applied at least to the areas experiencing the greatest exposure. Obviously, the greater, more severe the exposure, the shorter the lifespan of the product.

Surface preparation and application The longevity of any top coating product is directly linked to the quality of the product, the quality of the surface preparation and application technique. Painting or staining over a poorly prepared surface will certainly cause early product failure. Poor applicator tools will leave weak spots in the coating film which contribute to early film breakdown.
Proper application requires the coating to be distributed evenly over the surface, at the proper spreading rate (the number of square feet per gallon coverage) indicated on the product label. Uneven application will become apparent after the coating weathers for a period, and the undercoat or substrate color begins to show through in small patches here and there. Stretching the product too far, e.g., exceeding the square foot coverage intended for the product, will reduce the lifespan of the product dramatically.

Water Repellent Pre-treatment. The use of a paintable water repellent or water repellent preservative prior to priming (for continuous film coating) is highly recommended, particularly for lap or butt joints on siding or millwork. This will help prevent moisture from wicking into the wood at these junctures, thus reducing the shrinking and swelling, which over stresses the coating, resulting in cracking and peeling. Use only products over which paints can be applied.

Product quality There are two basic ways manufacturers may reduce the costs of their products to create more profit, or meet lower competitive price situations. They can use less expensive, lower performance chemical ingredients or they can use quality ingredients, but use lesser quantities of these or blend them with lesser quality chemicals. In either case, product performance will be reduced, resulting in earlier product deterioration. This not only raises the annual maintenance cost considerably, in labor and materials, but can cause excessive problems in repairing or removing the coating prior to the application of the next coat. In some cases, a brand's "best" product may be decidedly inferior to another brand's standard product. Product lifespan guarantees are often little more than marketing tactics, since no manufacturer can be certain of the exposure the product will be subjected to, or the quality of the surface preparation and application. They have relatively little cost in replacing the product compared to the labor involved in repairing or recoating.

Products manufactured and marketed for low competitive prices may be much more expensive in the long run than products made for performance.