Coqtings provide extrq protection for ileqted wood

A LTHOUGH already-built struclA.tures are unaffected by the coming phase-out of CCA treated wood for residential uses, the EPA suggests refinishing-not ripping out-for homeowners who are worried about chemical exposure. Surface coating decks, picnic tables, play equipment and other treated structures may provide an added precaution against leaching.

The EPA cautions that while available data are very limited, some studies suggest that applying certain penetrating coatings (such as oil-based, semi-transparent stains) on a regular basis (once per year or every other year depending upon wear and weathering) may reduce the migration of wood preservative chemicals from CCA treated wood.

Unfortunately, the efficacy of coatings or sealers in preventing leaching has undergone little evaluation. In the most cited study, last year, researchers at the Forest Products Laboratory evaluated the ability of three common coatings to lessen leaching from CCAtreated wood. Matching specimens of treated 2x6 lumber were given a latex primer followed by a coat of outdoor latex paint, an oil-based primer followed by one coat of oil-based paint, or two coats of a penetrating oil semitransparent deck stain. The specimens were exposed for three weeks to 30 inchesof artificial rainfall. Researchers then collected the water running off the specimens and analyzed it for preservative components.

All three coatings reduced leaching of arsenic pentoxide, chromium trioxide, and copper oxide by more than 997o compared to uncoated specimens. None of the water collected from the specimens coated with latex or oilbased paint contained any detectable copper, chromium or arsenic. In some cases, water collected from oil stained specimens had detectable levels, but the highest level of arsenic detected in these samples was still well below the EPA's drinking water standard.

In helping consumers and contractors select a finish, deulers should be aware that, in some cases. "f ilmforming" or non-penetrating stains (latex semi-transparent, latex opaque, and oil-based opaque stains) on outdoor surfaces such as decks and fences are not recommended, as subsequent peeling and flaking may ultimately have an impact on durability as well as exposure to the preservatives in the wood.

Chemical manufacturer CSI recommends

"a good quality oil-based product. Transparent or semi-transparent products work best. Solid products just lie on the wood and do not move with it. This results in peeling."

Unlike some other wood preservatives, CCA not only readily accepts most coatings, but it has been shown to enhance the service life of paints, stains and water repellents.

Still, there are a few potential problems users should be aware of. Excessive moisture in the wood can impede penetration of finishes. While high permeability enhances a species' treatability, it reduces its finish-holding capabilities. And, CCA-treated wood's light brown to bluish-green color may show through light-colored coatings, requiring the use of darker colors, more opaque finishes, and/or a second coat.

Critical to successful finishing of CCA-treated wood are proper surface preparation, application procedures and coverage rate. More is usually not better and over application can result in premature coating failure.

Applying certain

penetrating coatings on a regular basis may reduce the migration of wood preservative chemicals.

"All purpose" coatings from firms such as Cabot Stains and Wolman Wood Care Products work with numerous types of wood, including pressure treated lumber. Other coatings makers have special products just for treated wood. such as Performance Coatings's Penofin (penetrating oil finish) for Pressure Treated Wood.

Expect to see new coating Products specially formulated to prevent leaching of chemicals from treated woodas well as existing products relabeled or remarketed to stress that feature.

Northstar Vinyl recently introduced TruSealer, a plastic wood sealer that penetrates deep into the wood surface and quickly dries to form a plastic seal. The synthetic seal protects the wood from moisture and, at the same time, locks in the wood preservative chemicals. The manufacturer claims TruSealer is the only sealer on the market that has been proven to encapsulate CCA and prevent leaching.