ASSESSING THE CURRENT STATUS OF YOUR WOOD
The first place to start with any exterior wood project is to understand what you are working with. Exterior wood, no matter if it’s decking or siding, can have a variety of challenges that need to be addressed before staining.
It’s important to understanding the condition of your wood surface before you strip as not all decks need to have the previous coating removed. For example, if you are going to lighten your wood and go from a solid to a semi-transparent finish, or make a dramatic color change, then stripping is required. The same is true if the surface of the wood has experienced extreme weathering and cracking and blistering of the previous coating has occurred.
Mold and Mildew
This is one of the most common occurrences on exterior wood surfaces and is usually mistaken for dirt. This can show up as small black spots or greenish/black fuzzy spots. Left untreated mold and mildew will start to rot the wood surface.
You will notice previous coats of stain or paint that are failing on the surface will begin to peel and pull away from the wood substrate. Unsound surfaces such as these must be removed or sanded down to a sound surface. A tape test can help determine if the coating is tightly sticking to the wood.
This reddish brown discoloration is caused by moisture drawing tannins to the surface. Though it wonât harm an existing coating, it is visually unpleasant and it could affect adhesion of a stain in high enough concentrations.
Wood will begin to show signs of weathering after sitting uncovered or if a previous coat fails. Weathering usually presents itself as a grey or silver appearance on the surface. Other signs include wood that flakes or appears very soft when pressed with a fingernail. Weathered wood must be removed from the surface prior to staining or painting.
Beware, new wood may need preparation too. Mill glaze on fresh cedar or newly treated lumber has a tendency to repel stains. Mill glaze is a result of sawing of the wood and actually closes the grains to prevent penetration of the stain. This can be resolved by sanding the wood lightly. On the other hand, freshly treated lumber will not allow a stain to adhere until the treatment has worn down and the lumber dries out. The presence of either of these issues can be determined by a simple water test. Wet the surface with a garden hose and see if the water beads up. If so, you will need to lightly sand. In the case of treated lumber we recommend that you test the surface every few months for penetration, once the water penetrates you can stain the surface.