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| Sealers & Finishes for Pressure-Treated Lumber |
Although treated wood is protected against decay and termite attack, the
application of a water-repellent sealer to all exposed wood surfaces is
recommended upon completion of construction. This sealer will help control
surface checking (splitting or cracking) and provide an attractive appearance.
Over time, reapplication of a sealer is recommended, perhaps every year or
two; follow the manufacturer's instructions.
| Special Formulations |
| Formulations of wood preservatives are
now available that include a water-repellent
component, and even color additives.
Marketed under a variety of brand names,
these treatments provide convenience as
well as optimum long-term appearance for
outdoor projects. Consult your local lumber
dealer about the availability and finishing
recommendations of these special
treatments in your area.
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Over several months, pressure-treated Southern Pine lumber will weather
naturally to an appealing silver-gray color.
Treated Southern Pine lumber will accept a finish similar to untreated
material. Most importantly, Southern Pine should be dry before any type of
finish is applied.
Following construction, most manufacturers of stains and paints
recommend a waiting period - from a week to two months - before applying
a finish to treated wood, if the project was built
with lumber that was not kiln-dried after
treatment (KDAT).
Most paint manufacturers recommend two
coats of a good-quality acrylic latex paint for best
results on treated Southern Pine. When applying
any type of finish, be certain to follow the
recommendations of the paint or stain
manufacturer.
Fences
Fences are fully exposed to the weather, and have at least some parts in
contact with soil. Care must be exercised in selecting and applying a finish to
obtain a reasonable service life.
Many fences are left to weather naturally. However, if a finish is desired,
semi-transparent penetrating stains or water-repellent sealers/preservatives
that contain a mildewcide (or otherwise are resistant to mildew) are preferred.
These finishes are absorbed into the wood without forming a film; they do not
crack or peel. Stains come in a variety of colors and show the wood grain.
If paint is to be used, liberally brush the surface plus all ends and joints with
a paintable water-repellent/sealer preservative and allow the surface to dry for
at least two warm, sunny days before painting. Apply one coat of a good-quality
stain-blocking acrylic latex primer, followed by two topcoats of a good-quality
acrylic latex exterior house paint.
When repainting, scrape all loose paint from the wood, then use a stiff
bristle brush to remove any remaining loose paint and dirt. Next, brush on a
paintable water-repellent sealer/preservative. Apply it liberally to exposed
ends of boards or pickets and to all joints. Let the treated wood dry, then apply
acrylic latex paint.
Varnish finishes and solid-color stains are not recommended for fences
because they will not withstand sun and rain and will require frequent
refinishing.
Decks & Porches
Decks and porches present a particularly severe exposure for both the wood
and finishes. Most wood members are in a horizontal or flat position. These
horizontal surfaces, especially in decks, are often exposed to the direct rays of
the sun and tend to collect moisture, so the weathering process is greatly
accelerated. As repeated cycles of wetting and drying occur, checks tend to
enlarge rapidly into cracks and, along with the end-grain surfaces, begin to
retain moisture. The conditions for decay and insect attack caused by the
presence of moisture are thereby greatly improved.
Any film-forming finish is likewise subjected to excessive stress because of
the continuous shrinking and swelling of the wood that results from changes
in its moisture content. Furthermore, the finish is subjected to abrasive wear,
particularly in high-traffic areas. By design, porches are somewhat protected,
so the conditions are not normally as severe as those with decks; however, the
same conditions — moisture, sun, and abrasive wear — are usually present at
least periodically.
For fully exposed decks, a water-repellent sealer or a penetrating semi-transparent
stain may provide the best finishing solution, even on wood that
has been pressure treated with preservatives. Special formulations made
specifically for decks are available. These penetrating deck finishes, at least
the water-repellent sealers,
may have a shorter service
life than paint, but they are
more easily renewed. For
severe exposures, the finish
should be renewed annually;
spring is usually the best
time. Light-colored
penetrating stains will also
last longer than dark ones on
flat surfaces subjected to
traffic, because light stains
show the least contrast in
grain color as wear occurs. The penetrating finishes need to be refinished
every 1 to 2 years.
To refinish, a thorough cleaning of the wood with a stiff bristle brush is
usually adequate before applying the water-repellent sealer or penetrating
stain finish. Paint and solid-color stains, particularly in these applications, are
likely to peel. Laborious scraping and sanding before refinishing will usually
be required for these finishes. Therefore, paint and solid-color stains are not
appropriate for fully exposed decks.
The bright color of the wood on weathered decks can be restored (and
surface mold and mildew can be removed) by application of commercial
products (labeled as deck cleaners, brighteners, or restorers). These products
may remove the weathered wood surface; some care should be exercised not
to remove excess wood. Color can also be restored using a liquid household
bleach. The bleach is usually diluted with water (1 part bleach, 3 parts water)
before it is applied to the deck. The bleach solution should be thoroughly
rinsed from the deck with water. If the deck is to be finished after cleaning,
allow 1 or 2 days drying time.
Paint may be used successfully on roof-protected porch floors. For
optimum results, first treat the wood with a paintable water-repellent
sealer/preservative. After the floor dries, a primer and two topcoats of porch
and deck enamel should be applied. Porch enamel is especially formulated to
resist abrasion and wear. Solid-color stains should never be used on flat
surfaces such as decks and porches, because of their low resin content.
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