Pressure-treated wood needs to be dried before painting

By Gene Gary
Copley News Service

Q: I read your advice on refurbishing an older wood deck. My question concerns the new deck we recently built with pressure-treated wood. We've had conflicting advice on preservative treatments for it. Is the green cast to this wood stainable?

A: There is some confusion about the treatment and care of pressure-treated wood. Once treated, pressure-treated wood is often guaranteed to withstand bugs and fungus for years. However, if left unsealed, it can weather badly from continual exposure to rain and sun. There are treatments that will protect the wood and enhance its appearance.

The pressure-treating process leaves wood fairly saturated with preservative. Normally this wood is air-dried before shipment to lumberyards. But often it remains too wet (above 19 percent moisture content) for paint or stain to adhere properly.

If you want to paint or stain your pressure-treated deck right after construction, it's recommended that your build with pressure-treated wood that is designated "KDAT" (kiln dried after treatment). Though more expensive than air-dried wood, kiln-dried treated wood is dry enough to accept paint or stain immediately.

If you've already built with pressure-treated wood that has only been air-dried, the best approach is to wait several months or even a year before applying any kind of finish. You'll be able to tell by feeling and looking at the wood whether it's dry enough for painting or staining. Natural weathering and drying tends to remove the green appearance caused by deep penetrating chemicals used to protect the wood.

There is a product recommended for immediate use on air-dried, pressure-treated wood. The Flood Co. (800-356-6346) makes an easy-to-use protector called Seasonite for new exterior wood, including pressure-treated wood. This is not a durable staining finish, but it will help reduce splitting, cupping and warping during the drying process and provides a sound surface for later finishing.

The best low-maintenance finish once the wood has weathered and dried is a penetrating stain. However, if you like the natural look of Seasonite, this product can be reapplied for protection.

It's also best to clean your deck with a deck cleaner every year or two, followed by another application of Seasonite, which will keep the wood looking light and natural.

To restore color when the wood has started to turn gray, other Flood products include their deck cleaner, Dekswood, and for color restoration, Flood's CWF-UV stain in clear or toners. Other manufacturers specialize in product lines recommended for pressure-treated wood. The Koppers Co. markets Wolman Protection products including RainCoat Water Repellent and Wolman's Deck Stain (which contains a water repellent), formulated to tint and protect all types of wood used outdoors.

Wolman's Deck Brightener is a product formulated to remove dirt, mildew and algae from pressure-treated wood and untreated wood. Thompson's is another producer of several products -- Thompson's Water Seal, Thompson's Wood Protector and Thompson's Water Seal Exterior Stain -- designed to treat and protect pressure-treated exterior woods. Sherwin-Williams markets a complete system of Cuprinol products to protect and preserve your deck's finish. All of these products are readily available nationwide.

Q: I followed the advice in one of your columns regarding deck refurbishing and used a commercial deck cleaner. I then rinsed the surface with a power washer. Although the deck was clean when it dried, the wood was raised and rough instead of the normal smooth surface. What should I do at this stage? Did I use too much water, or is it possible the deck cleaner was the cause of this problem?

A: Most likely the power washer was set at a pressure setting too strong for the wood. When the pressure is too much, the stream of water will chew the wood. In fact, you don't need high pressure at all to clean a wood deck; a garden hose and nozzle will do just fine.

Now you will need to sand the rough surface using coarse-grade sandpaper and an electric sander. Follow this with another sanding using a medium-grade paper. Avoid excessive sanding that would tend to remove a sizable layer from your wood decking. All you want is a smooth surface.

When you have finished, vacuum the area to remove residue left by the sanding process and apply a wood preservative for protection.

Send e-mail to copleysd@copleynews.com or write to Here's How, Copley News Service, P.O. Box 120190, San Diego, CA 92112-0190. Only questions of general interest can be answered in the column.