Pressure-treated lumber is permeated with chemicals to make it more durable under a variety of weather conditions and protect it from termites. Popular uses for the wood include decks, patio furniture and gazebos. Nearly any wood stain for outdoor use can be applied to the treated lumber, but the wood must be clean and thoroughly dry.

On the Other: If You Stain Too Soon, You'll Have Problems

Treated lumber begins drying as soon as the chemical-infusion process is complete. According to custom deck builder Michael B. Martin, the wood leaves the lumberyard still wet and it must dry before application of any stain. Applying stain when the wood is still wet could result in "bubbling" from moisture in the wood trying to seep out, Martin says. It also could seal too much moisture inside the wood, which could lead to fungus growth or rotting.

Bottom Line

Experts say that treated lumber should dry for a minimum of six weeks after being installed and exposed to the environment before applying a deck stain. However, be sure to take into account factors such as climate and the dryness of the wood when installed. It is better to err on the side of waiting longer; the wood's appearance will not be affected, and if you apply stain too soon it may create serious appearance and structural issues.

Source:

Michael B. Martin blog

Southern Pine by Design

The Natural Handyman