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Q.We are planning to use pressure-treated wood as exterior trim on a house with fiber-cement siding. The siding will be finished with acrylic paint. Is pressure-treated wood appropriate for use as exterior trim? What precautions, if any, are necessary when painting pressure-treated wood? Can we use the same acrylic paint we will be using on the siding, or should we be using an oil-based paint?

A.Wood finishes expert Bill Feist responds: Most pressure-treated wood sold in lumberyards is treated with CCA (chromated copper arsenate). Although this type of pressure-treated wood is paintable, be aware that painting is possible only when the wood has been cleaned (using soapy water and a stiff bristle brush, followed by a clear water rinse), and allowed to dry thoroughly. Getting the wood dry can sometimes be a problem, because treated wood is often sold very wet from the treating process. Depending on the climate and drying conditions, it may be necessary to dry the wood for several weeks before painting.

An exterior all-acrylic latex house paint would be the best choice for painting pressure-treated wood. Exterior acrylic latex house paints can normally be used on many different substrates — aluminum, galvanized steel, masonry, concrete, brick — as well as pressure-treated wood and fiber-cement siding. However, always check the label on the paint can to be sure it is recommended for use on wood products.

If possible, find a manufacturer who also has an acrylic latex primer. The combination of latex primer and topcoat has been shown to give the best overall paint performance on treated wood. I would not use oil-based paint, which does not perform well on pressure-treated wood.

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.

Finally, since pressure-treated wood has a tendency to warp and crack rather easily, the trim would need to be carefully and securely nailed or screwed.