Deck Treatment...

Whether or not you intend to paint the wood, pressure- treated exterior trim should be sealed with a water- repellent preservative as soon as the surface is sufficiently dry. This will protect cut ends and help keep the wood from checking, cupping, and warping as the wood dries out. If this is the only treatment, it will need recoating every one to two years. Factory-sealed treated lumber is now available that only requires treatment of cut ends when installed.

The most common treatment for pressure-treated wood is an oil-based, semitransparent stain. Since this type of finish is relatively permeable to moisture, for best results apply it over a sealer or over factory-sealed lumber. While the sealer can be applied to wood that is still wet inside, it is best to air dry the wood before staining. This will take from a few days to a few weeks, depending on conditions, with two weeks on average. Two coats of an oil- based, semitransparent stain over a sealer should last several years. The second coat should be applied before the first coat dries completely, or the second coat cannot penetrate the wood.

If a painted finish is desired, you will need to seal the wood first and allow it to dry for two to three weeks before applying a compatible primer and two coats of 100% acrylic top coat. The longer the wood dries, however, the greater the risk that UV radiation will damage the wood surface, interfering with the paint’s adhesion. To avoid these problems and the long delays, consider using kiln- dried treated lumber that can be finished immediately.