Many homeowners like to have a deck in their backyard to provide an easily clearable, beautiful space for entertaining friends and to serve as a flat, stable surface for chairs so that people can sit comfortably. There are many different types of decking materials, including brick, tile, concrete, flagstone, and wood. Wood decks are very popular because they are relatively inexpensive to install and many people like the appearance of natural wood. But because wood is an organic material and wood decks are exposed to the weather, they require more protection than other types of decks.

   Water may be necessary for life, but rainwater can be detrimental to unprotected wood decks. Prolonged exposure to moisture can cause wood to decay and rot. Airborne molds, mildew, and fungi tend to grow on wet wood and accelerate deterioration. Wet wood also tends to either shrink or swell, allowing cracks to form. Because of these kinds of problems, many different products have been developed to protect wood decks.

   Water repellents are a general class of products containing a component that enables surfaces to repel water. Water repellent preservatives also include various chemicals such as fungicides that inhibit the growth of molds, mildew, and fungi. The percentage of the water repellent component varies from approximately 1% to 3% in different products.

   All water repellents need to be reapplied periodically in order to maintain their effectiveness. As a general principle, products that contain higher percentages of a water repellent component tend to provide better protection.