Overview: The benefits of primer
One of the most powerful tools in any
pro painter's arsenal is what goes
underneath the paint—primer. Primer
is an excellent problem-solver that's
less like paint and more like glue. It
sticks to whatever you're prepping and turns it into
a smooth, uniform surface that's ready for paint.
But if you've ever walked down the primer aisle
at a home center, you know the primer choices
are mind-boggling. To cut through the clutter,
we asked three professional painters, each with
20-plus years of experience, to give us their
recommendations for the best primers to use for
common painting challenges. Their experience
will help you choose the best primer for the job,
so your paint will look better and last longer.
Problem 1: Interior stains and odors
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Stain blocking primer
Stain-blocking primers can be oil or water based.
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Primers are generally white, but can be tinted.
Some stains will bleed right through most
primers and paints no matter how many coats
you apply. The same goes for severe odors like
smoke from fires and cigarettes.
The solution is stain-blocking primer, which
is available in oil-based (alkyd) and water-based (acrylic-latex) versions. Oil-based
versions give off a nasty smell and require paint thinner for cleanup, but
they're more reliable for blocking water-based odors and stains like rust, nicotine,
smoke, wood tannins and, of course, water (see “Shellac: The Original
Primer,” below, for dealing with severe stains and odors).
Water-based stain-blocking primers offer easy cleanup and less odor and come
in low- and no-VOC (volatile organic compounds) formulations. These work best
to block solvent-based stains like crayon, grease, ink and scuff marks. Both versions
are white, so it's a good idea to tint them gray or close to your topcoat color
if they'll be covered by dark-colored paint.
Do I Always Need to Prime Before Painting?
You don't have to prime previously
painted surfaces if the paint is in
good shape—no chipping or peeling.
Interior walls usually don't need
priming except in the case of stains,
repairs or a paint color that's drastically
different. Interior painted
woodwork usually needs spot priming
at a minimum. Exterior paint
takes such a beating that it almost
always needs priming.
Problem 2: New Drywall
The mud used on the seams of drywall absorbs paint differently than the rest of the
drywall. This difference in porosity can cause blotchy, dull areas under the paint
(a problem called “flashing”) and an inconsistent sheen. Prevent this problem by
using a drywall primer-sealer.
If you're an ace drywall finisher and your walls are perfectly smooth, you can
use a standard drywall primer-sealer. But if you're like most of us, your finished
drywall probably has some tiny pockmarks, fine ridges and scuffed paper from
sanding. The solution to those minor imperfections is a “high-build” drywall
primer-sealer. This heavier-bodied primer-sealer is a little more expensive than
standard primer-sealer, but it does a better job of leveling and filling in rough or
uneven drywall construction. (Sorry to say that not even a high-build drywall
primer can hide a terrible tape job.)
Alternatively, if your drywall is relatively smooth and the topcoat is going to be
a flat paint, you can skip the primer and use two coats of high-quality self-priming
water-based flat paint (see “Self-Priming Paints,” below). The heavy-bodied paint
resins in self-priming paints seal the surface and fill imperfections (which are less
visible in flat paint anyway).
Tip: Paint within
48 hours of priming.
are formulated to
with the paint
applied over them.
primed, you should
paint over it within
a couple of days or
it will lose its
you'll need to
DIY Success Story“I did a good job of taping the drywall
in our new family room, but there
were definitely a couple of spots
where the mud got a little thick. The
guy at the paint store recommended
a primer made especially for imperfect
drywall. I was skeptical, but
once I'd primed and painted the wall,
nobody (not even me) could tell
where the rough spots were.”
Problem 3: Moisture-prone areas
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Use a stain-blocking primer
Apply a stain-blocking primer
to high-humidity areas to prevent
mildew and peeling on interior
walls and blistering on exterior
The high moisture in areas such as kitchens,
closets, bathrooms and laundry rooms can
cause paints to mildew, flake or peel. Interior
moisture moving outward through the wall can
cause peeling, bubbling or blistering on exterior
walls as well. Use a vapor barrier primer to
seal the surface and minimize the passage of
moisture through the walls to the outside. If
mildew is a serious concern, use a stain-blocking
primer to prevent mildew stains from
bleeding through the topcoat and then use a
topcoat that specifically resists mildew (check the label). Make sure to kill any
mildew with a one-part bleach and three-parts water mixture before priming.
Problem 4: Repaired walls
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Prime patched areas
Prime patched areas before painting.
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Repair not primed
A drywall primer-sealer seals the porous surface so paint won't
sink in and look dull or blotchy.
Like new drywall mud, wall patches absorb paint differently
than the rest of the wall. To prevent flashing, cover everything
from dabs of spackle to broad patches of joint compound
with a good-quality drywall primer-sealer.
However, if you have plaster rather than drywall, any
repairs you make will
need a coat of oil-based
Without it, lime stains will
form around the repairs
and will bleed through the
topcoat. This applies to
tiny caulking and spackling
touch-ups as well as
major repairs with joint
Problem 5: New interior bare wood
It's important to prime bare wood to seal the thirsty surface,
hide imperfections and bind the wood fibers to make the
surface more uniform. Slower-drying oil-based primers,
such as an enamel undercoat primer, provide better adhesion
and are easier to sand than water-based primers. If
you use a water-based primer, it's likely to raise the grain of
the wood and require more sanding before you apply the
Problem 6: MDF (medium-density fiberboard)
Use an oil-based primer unless the MDF comes
preprimed. Don't use a water-based primer, which can
soak into the surface and cause it to swell. Before priming,
sand the surface smooth and make sure it's dust-free.
Prime all surfaces, including the board edges.
Spot-priming with shellac
Shellac: The Original Primer
Shellac has been used for
centuries and is still the best
primer for a few situations.
It's an excellent choice if you
need a fast-drying spot
primer to prevent wood
knots, rusty nail heads and
the most severe water-based
stains and odors such
as smoke, soot, urine and
through the topcoat. Shellac
(a common brand is BIN)
can soften in direct sunlight
and by itself isn't durable
enough for exterior use. If
you use it for exterior spot priming, prime over it with a
water-based exterior primer before applying the topcoat.
Shellac requires denatured alcohol for thinning and cleanup.
For the best results, make sure the surface is completely
clean and dust-free before applying.
The photo shows spot-priming nail heads
and knots with shellac to
prevent rust and wood
resins from bleeding
through the topcoat.
Problem 7: Previously painted interior woodwork
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Priming a door
priming, use a
roller on the
door and a
2-in. brush on
such as casings,
For a smooth
paint job, sand
If the old paint is in good shape, there's no need to prime. But if the
paint is chalking or is chipped, use an oil-based enamel undercoat
primer after properly prepping the surface. An enamel undercoat
primer bonds well to previously painted surfaces and improves the
topcoat by flowing out to a dense, smooth uniform foundation without
laps or brush marks. Fast-drying primers like shellac and many
water-based products dry too quickly and become brittle. This can
cause lap marks and makes it harder to sand and get a smooth base for
the topcoat. Oil-based primers sand well but dry more slowly (some
can take 48 hours or longer). If you want to use a water-based product,
look for a high-build acrylic-latex enamel undercoat that's specifically
designed to be sanded.
Problem 8: Drastic paint color change
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You can buy some primers pre-tinted to help in top coats cover better.
When you change from a light color to dark or vice versa, it
can take many coats of paint to hide the existing paint
color. Tinting your primer gray or a color similar to your
finish paint reduces the number of topcoats you need to
apply to get good results. Not all primers can be tinted darker
colors, so make sure to choose one that can. Even without
a drastic color change, tinting your primer gray will help enhance the
color of most dark-colored interior paints and improve a primer's “hide” (how
well it covers the imperfections and color of your wall surface).
Problem 9: Exterior wood
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New exterior wood
Always prime exterior wood with a high-quality primer.
Exterior paint takes a beating.
And one of the best ways to
extend the life of your paint job is
with a good primer. So unless
you enjoy scraping paint, spend
about $30 per gallon on a top-quality
acrylic/latex exterior primer.
Look for “100 percent acrylic” on
the label, and make sure the
wood surface is clean, dry and
dull (no sheen). On properly prepared
walls, a high-quality
primer can double the life of your
exterior paint job.
Tip: Use a primer and paint from the same
manufacturer. Many primers are formulated
to work best with certain paints.
Problem 10: Old exterior paint
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Pressure-washing painted siding
Pressure washing removes loose paint and
built-up grime and improves paint adhesion.
Keep the nozzle at least 16 in. away
from the wood.
If exterior paint is in great shape,
there's no need to prime. But that's
hardly ever the case. At the very
least, you'll have to spot-prime any
bare wood where the paint has
peeled away. Use a high-quality
acrylic/latex exterior primer. And if
the paint is “chalking,” you'll have
to prime the entire surface. To detect
chalking, just wipe the paint with a
rag. If the rag picks up colored dust,
you've got chalking. Before you prime, thoroughly scrub and power-wash the
siding. Peeling areas with dirt and mildew must be cleaned, scraped or sanded
before priming. Preparation is the key to a long-lasting paint job. If it's not
done correctly, the surface will peel again within a year or two.
Problem 11: Exterior woods that stain
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Oil-based stain-blocking primers keep stains from bleeding through the topcoat.
Cedar, redwood and
a few less common
woods contain lots
of pigments, called
tannins, that will
bleed through standard primer
and paint. To stop the bleeding,
use an oil-based stain-blocking
exterior primer for larger areas
and top with an acrylic/latex finish
coat. If you're going to use an
oil topcoat, use only an oil-based
primer. However, thanks to new
water-based paint formulations,
you can paint an acrylic/latex topcoat
over either an oil- or water-based
Self-priming paints hit the market
almost a decade ago with the
promise of paint and primer in
one can. The early reviews were
mixed, but paint technology has
continued to improve. The newest
self-priming paints include Behr's
Premium Plus Ultra, Sherwin-Williams' Duration and Benjamin
Moore's Aura paints. The manufacturers
tell us that these thick,
high-build, low-VOC paints provide
a dense, hard, durable paint
film that resists moisture and
mildew, all without using a separate
prime coat. Prices for these
self-priming paints range from
$35 to $55 a gallon. For more
information, visit behr.com