Painting Pressure Treated Wood
We asked Rust-Oleum their thoughts on painting current pressure treated wood products. Their recommendation is to wait 6 months so that the wood is thoroughly dry and cured since is wet from the pressure treated chemicals and coatings they use. Otherwise as the moisture is trying to escape from the wood will cause any coating to lose adhesion.
They recommend their Zinsser Cover Stain Primer. Please note this should not be applied to a walking surface.
Pressure-treated wood may not be the best choice for exterior trim, since most pressure-treated wood is southern yellow pine, a species that is not particularly good at holding paint. Southern yellow pine, whether or not it is pressure-treated, does not hold paint as well as western red cedar. Since most pressure-treated wood has knots and other defects, any lumber used for exterior trim would need to be carefully selected to find boards that are as clear as possible. Although some lumberyards do sell premium grades of pressure-treated wood for exterior trim, this grade may be difficult to find.
If the new pressure treated lumber shows any signs of mold, mildew, or algae growth, clean the surface just as you would for prepping for any paint job, using a dilute solution of chlorine and water. Surprisingly, mildew grows quite well on unprotected, pressure treated lumber and it must be removed before painting.
Some experts do not recommend clear waterproof sealers on pressure treated lumber, as the nature of the lumber eliminates the ability of these sealers to penetrate properly. Sifting on the surface, these sealers can actually attract dirt, mold, mildew and algae causing more damage than you would get if you just left it alone. Staining pressure treated lumber is also not recommended, again due to the inability of stains to properly penetrate into the lumber. It is our experience that a proper primer and topcoat of 100% acrylic premium paints has the best chance of adhering and withstanding the excessive moisture and shrinkage of pressure treated lumber.
How do you know when it’s ready to paint? Once the wood feels dry to the touch, sprinkle a bit of water on it. If the water soaks in, then the wood can be painted. If the water beads up, go back to playing the waiting game. Note that for a time-sensitive project, it may be wise to choose pressure-treated wood that was kiln-dried after treatment (KDAT). You can paint KDAT wood sooner. A six months drying period is normal for any wood above a 15% moisture reading.
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