There are many brands and types of deck finishes, but none is perfect
for all situations. Ask neighboring deck owners what they've used to keep
their decks looking good, and how often they apply it. Also, research the
pros and cons of different ingredients before choosing the finish for your
deck. The tips below should help.
The many deck finish products basically are different combinations of a
few ingredients: water repellent, resin, preservative, and/or UV blockers,
absorbers, and inhibitors. Less expensive products usually contain fewer
and lower-quality ingredients and perform less well.
Most products will need to be applied every year or two, depending on
your climate and how much the deck is used. However, some higher-end
finishes have proved more durable and typically last four years, even in
regions with harsh weather. Their success lies not in the type of
ingredients, but in how well they penetrate the wood. The more they soak
into the wood, the longer the finish lasts.
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A Note About Varnish and Polyurethane
Though strong and long-lasting, polyurethane and varnish are not
recommended for decks since they form a hard, inflexible surface film.
When deck flooring moves due to moisture and temperature changes,
this film will crack and may even flake. Once that occurs, you'll need
to completely strip the old finish and apply a new one. Polyurethane
and varnish also do not protect against the sun's UV rays, meaning
that your wood will turn gray. Moreover, once the surface cells have
been destroyed by the sun, the finish will flake off since it has nothing
to adhere to.
Water Repellents
A good deck finish will repel water while remaining flexible enough not
to crack. Most deck finishes repel water with paraffin and/or oil (either
tung oil or linseed oil). The finish is manifest when water beads after it
has rained. Under rainfall and traffic, paraffin and oil finishes will wear
out fairly quickly and will need to be reapplied. Alkyd resin is a longer-
lasting—and more costly—water repellent which soaks into the wood
to seal it from moisture. A heavy dose of resin gives decks a
permanent "wet look" that many find attractive. However, it also can
impart an amber or yellow cast to your deck
Preservatives
Most preservatives contain a combination of fungicide, mildewcide,
and insecticide. All-purpose deck finishes usually contain a mildly
protective amount of all three. But if your climate presents serious
problems with fungus, mildew, or insects, you may need to bolster the
low-level protection of an all-purpose finish with a separate treatment
UV blockers, Absorbers, and Inhibitors
If you liked the original color of your deck and want to keep it from
turning gray, coat it with ultraviolet protection in the form of UV
absorbers and blockers. These solid pigment particles absorb or
reflect UV rays to minimize their damage. However, the very pigments
that keep the sun from graying the deck will add color to the wood. It
doesn't take much pigment to block the sun's rays, so if you choose
carefully, your wood's appearance needn't change drastically. But be
aware that your wood will not look exactly as it did when you first
installed it. Alternatively, choose a more expensive finish containing UV
inhibitors—compounds which actually disrupt the chemical action
caused by UV light. The advantage is that no pigment is required, so
you can more nearly retain the original look of your wood. But the sun-
protective chemical reactions of UV inhibitors ironically cause them to
break down and become less effective. So not only are these finishes
more expensive, they are significantly shorter-lived than pigmented UV
blockers and absorbers. This means that if you don't re-apply them
often, your wood still will turn gray.
Clear Finishes
Truly clear finishes usually contain a water repellent plus a
preservative. Use these if you want your wood to gray. They will hardly
change the appearance of your wood (unless they contain resin) and
will help your deck last longer than it would without a finish. When
staining a deck, you may want to use less-expensive clear sealer for
the underside where sun and discoloration don't matter. Just make
sure that no clear finish is sprayed to the topside, where it could
change the color of the stain. Some products labeled "clear" actually
contain pigments for UV protection, so are not really clear. Others
contain UV inhibitors which will keep your deck its natural color without
pigment, but only if the treatment is frequently reapplied
Solid Stains and Paints
Solid-color stains essentially are thinned paints that let a bit of the
wood grain show through. Solid-color stains are designed for siding
and are not appropriate for surfaces that are walked upon since they
will wear away quickly. For a solid-color deck, porch-and-deck paint is
more durable than stain, though it has serious drawbacks. Unlike
stain, paint does not soak into wood, but rather forms a thin film on
top. It protects the wood it covers, but decks have uncovered places,
such as the undersides and edges of deck pieces, that a brush may
not reach. Plus, when paint cracks due to the wood's expansion and
contraction, any water seeping into the wood is trapped by the paint
which then encourages warping, cracking, and rot. Paint can,
however, work well on tongue-and-groove deck flooring, since it
completely covers the exposed wood. All in all, it's best to use paint or
solid stain only on vertical surfaces such as posts, balusters, and
skirting that do not endure wear.
Making Pressure-Treated Wood Look Like Cedar or Redwood
Brown pressure-treated lumber looks pretty much like stained
redwood or cedar. If the color fades over the years, you can restain it
using a semi-transparent deck finish. Apply the finish in a small,
inconspicuous spot, waiting a few days for the color to settle in before
coating the deck with it. Green pressure-treated wood is best left
uncoated for about a year to let it gray somewhat. Then apply either
wood bleach (oxalic acid) or a product specially made for cleaning
pressure-treated lumber. Use a stiff broom or scrub brush to dig out
grime. Rinse the deck thoroughly and let it dry completely. The gray
will have disappeared and the wood will be somewhat less green than
it was originally. To achieve a redwood or cedar color, experiment
with light, semi-transparent stains. Products called "toners" are made
for this purpose.
Applying Penetrating
FinishIf your deck is constructed as cold weather approaches, it
may be too late to apply the finish, especially as you may need to
wait a month for the wood to dry. Finishes should not be applied
when the temperature's at or below 40 degrees. It's okay, however,
to leave the deck over winter and stain it in the spring. If some
graying occurs, first wash it with wood bleach. When applying a
penetrating finish, you want the wood to absorb as much as it can.
So don't hesitate to apply penetrating finish liberally; it won't leave
brush marks since it's absorbed, and excess finish can simply be
wiped off. The most common mistake is not applying enough finish
to saturate the wood fibers. In fact, end grain (such as the ends of
posts or decking pieces) absorbs finish almost as soon as it's
brushed on. Check these spots during application, and reapply the
finish until the wood stops absorbing it. Words of caution: avoid
breathing finish vapors or spray mists. Wear rubber gloves and
long-sleeved garments during application to reduce exposure and
minimize the chance of skin irritation. Always wear goggles or safety
glasses to protect yourself from backspray or drips
How to Apply Finish to Your Deck
