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.