From Engineering on December 31, 2007 in Decks and Patios
Here in the Bay Area, the first week of winter has already brought several days of much needed rain. With the cold season just beginning and spring showers in the near horizon, homeowners with wood decks spend less time barbequing and more time looking out at their outdoor structures, trusting that the wood finishes applied last summer are holding out.
Now that the rain is testing your decks endurance to the elements, you may be wondering when you should apply the next all-important coat of finish. Weve provided some helpful reminders about wood finish to help keep you on the alert about deck maintenance, whether you have an existing structure or plan to build one as soon as the weather gets dry.
Preparation in the form of washing and sanding a deck is critical prior to applying a finish. You wouldnt want to sand mildew deeper into the woods surface. It is also important that the wood is completely dry before you begin.
Protective wood coating is primarily classified into 3 groups: stains, sealants, and paint. Since paint peels, it is often isolated to railings as opposed to deck flooring.
Stains contain pigments that tint the wood while forming a protective barrier. They are more fluid than paint and can easily be applied with a cloth. Ranging from pale sandy colors to the deeper orange of redwood, stains are usually used on lighter colored wood such as cypress. Semitransparent or alkyd stains penetrate wood and never peel off. Solid stains are the longest lasting and provide additional UV protection.
Then there are finishes, clear or colored sealers that extend the life of wood, protecting it against wear and tear, preventing surface scuffing, and adding a lustrous sheen. They can be brushed or sprayed on after the stain or be used to preserve the woods natural color. The most widely used finishes are oil, varnish and polyurethane, shellac, lacquer, and water-based finishes.
Oil penetrates into the woods fibers but doesnt build up to a thick coat. Use a product such as linseed oil, which cures as well. Products that can build into thicker coats prevent moisture and vapor exchange more readily. A single coat of polyurethane, for instance, is more durable than multiple coats of a water-based finish.
Polyurethane and varnish are the most protective finishes but are also slow drying, making them prone to dirt and dust. Shellac, an alcohol-based natural resin, is not as protective but dries quickly. Lacquer is also fast drying. However, it is often sprayed on, and the fumes from spraying lacquer can be hazardous to your health. If this is a concern, consider using a water-based finish, keeping in mind that it will be less durable than other finishes and may hold visible brush marks.
Other ingredients to look out for in your wood finish are resins, which soak into the wood, are longer lasting and more expensive, and parrafins, which help repel water and are mixed with an agent for spreading. Preservatives are recommended to help prevent mold or mildew build-up. Also recommended are UV inhibitors to provide protection against the sun and help slow down the discoloration process.