There seems to be some confusion on the part of consumers concerning pressure treated decks. This is one of the most popular choices for deck lumber due to its durability and fair cost. Through our experience, we have found that many homeowners are under the impression that pressure treated wood does not need to be stained or sealed.
The main reason that some homeowners think this is due to the word “treated.” Many people believe that treated means that it’s already protected from the weather. Unfortunately, this is not the case.
The chemical treating process that is normally done at the lumber mill, is to deter termites and other insects from eating the wood and nothing more. Similar to railroad ties and utility poles being treated with creosote, pressure treated lumber for residential use is normally treated with preservatives like sodium borates and chromate copper arsenate.
The wood is placed inside a locked cylinder then vacuum and pressure are both applied to force the preservatives into the wood, thus “pressure treated.” Again, it’s all to deter bugs and some types of fungal decay but there is no protection at all from the sun’s UV rays or moisture.
Therefore, like other woods used for deck construction, pressure treated lumber needs to have an aftermarket deck stain or sealer applied to it for sufficient sun and moisture protection. When pressure treated lumber is protected properly with a deck stain, and maintained every couple of years, it can withstand the elements for a very long time.