A good wood stain meets environmental regulations (e.g., low levels of volatile organic compounds), penetrates the wood and gives it long lasting protection from the elements.
A good wood stain retains its color even after several years, is dirt and mold-resistant and protects the wood from cracking. If your deck was made before 2004, chances are it is made of chromated copper arsenate-treated wood. In this case, a semi-transparent stain would be ideal to penetrate the wood grains and seal in the arsenic. Equally important to applying a successful wood deck stain are the wood preparation and the applicator used to apply the stain. Completely sand off or clean the wood of old stain, dirt, oils and mold. For application, a synthetic brush or a roller with a short nap ensures that the stain is applied thinly enough to absorb into the wood grains.