One of the most common exterior paint failures we see is on painted wood surfaces, especially wooden window sills and door frames. Many times these failures are related to the loss of adhesion of a factory applied primer. Most primers used for preprimed windows and door frames are fast-drying, brittle, lacquer-based products, that trap moisture in the wood. This trapped moisture contributes to the growth of various lichens and fungi which continually thrive on the wood just beneath the coating surface, causing the primer to peel, along with the topcoat. The failure of coatings on preprimed wood trim and windows is widespread, yet preventable. Exterior wood primers must be breathable and flexible. For new construction and remodeling, we strongly encourage using exterior Acrylic primer for all new exterior wood. We discourage the use of factory preprimed wood for exterior service. We hope window and door manufacturers will soon change to superior performing, flexible, breathable Acrylic primer and coating systems.
The lumber used in construction today is mostly new growth forestry, with much less dimensional stability than the harder old growth wood of the past. What this means is that today’s wood expands and contracts and twists significantly if moisture content of the wood varies. Because of this dimensional change in wood, we need flexible coatings. Newer technology coatings are flexible, and microporous, allowing breathability.
Older technology products like oil based paints and primers, and spar varnish all continually harden as they age. Eventually these hardened coatings become brittle, and if wood expands, it cracks the coating, allowing moisture intrusion, and further expansion and contractions of the wood.
Trapped moisture leads to excessive expansion and contraction of the wood, which further loosens paint and caulking, leading to increased moisture intrusion. The continued deterioration of this top layer of wood fiber leads to premature paint failure.
We also see moisture entrapment as a result of the use of oil-based exterior paint products. We highly discourage the use of oil-based house paint and never specify it for our projects.
There are several common preventable sources of moisture intrusion. Commonly it is the result of an inferior caulking product or inadequate application. The failure of silicone caulk or siliconized acrylic caulking on brick is widespread, leading to premature paint failure and preventable maintenance expense and wood replacement. The acid curing nature of silicone caulk makes it unsuitable for adhering to usually alkaline brick mortar around windows. Many widely used caulking products are inadequate for most exterior applications. We strongly encourage builders, homeowners, and contractors to prevent numerous future problems by using only premium quality Elastomeric and urethane caulking for sealing and beautifying the home. Many paint failures are caused by the use of traditional acrylic caulking products. More caulking products now have the terms “Elastomeric” or “urethan ” on the label, but not all are created equal. We hope to increase awareness of superior performing products now available. Premium ELASTOMERIC or URETHANE caulks will always outperform most all latex or silicone caulks in durability and longevity.
Better Solutions
Our system of choice for most exterior wood is a field applied acrylic house paint primer to bare wood,( two coats if bleeding type wood), followed by 2 coats of premium acrylic house paint. We strongly discourage the use of factory primed wood products for exterior service.
When paint peels to bare wood, it is critical that the entire failed area is completely sanded to remove all damaged and greyed wood fiber. Otherwise, the new coating system will likely have premature failure. A top grade acrylic primer for exterior bare wood is our product of choice. Primer should always be applied before the application of any caulking product. The likelihood of early failure is greatly increased by caulking bare wood. Caulking before priming also leaves bare wood surface under the caulking providing a likely source of moisture intrusion should the caulking loose adhesion. Cracks to be caulked should always be primed to insure maximum adhesion of the caulking. Most exterior coating systems we create utilize ELASTOMERIC caulking and patching products,in conjunction with URETHANE based caulking products. We have found that most acrylic caulking products available (even 45 year) are inadequate in most exterior environments.