Painting Q&ABy Charles Gilley Jr. and Charles
Painting may be the last big task to happen on some jobs, said
painting contractor and instructor Charles Gilley to a roomful
of builders at JLC Live in Providence last year, but that
doesn't mean it's the last thing the builder should think about
— after all, what's on the surface is what the
customer sees. "We can make the carpenter's work look better,
or we can make it look worse," said Gilley, "but we need the
builder's help and cooperation to get the best possible
results." Whether paint performs well or poorly, said Gilley,
can depend on things that the builder, not the painter,
Gilley runs Charles Gilley Restoration Painting in Woodstock,
Vt. He and Charles Owens, a cabinetmaker and painting
contractor from Richmond, Vt., covered a broad range of
painting how-to and how-not-to topics in their 90-minute JLC
Live slide presentation, but the audience had plenty of
questions left over for a question-and-answer session
afterwards. In the following pages, we bring you some of the
lore the two men have accumulated along with the spilled paint
on their overalls. If we happen to leave out a question that
has you scratching your head, send us a letter, fax, or e-mail
— Owens, Gilley, and a few other experienced pros we
know are more than willing to help builders learn about
Q. When you prep an existing house for
repainting, should you power-wash before you scrape and sand,
or power-wash to remove dust after sanding?
Always wash first, then scrape
and sand. And wash just to clean off the surface dirt, not to
remove paint — blasting hard enough to remove paint
with a power-washer typically tears up the wood, and it also
can blow water into the walls under the siding.
A thorough job of scraping takes off any paint that no longer
has good adhesion to the wood, but it leaves sharp edges where
the remaining areas of well-attached old paint meet the newly
exposed wood. We sand after scraping in order to feather those
edges into the bare wood and create the smoother surface
required for fresh paint to go on at a consistent thickness.
Power-washing after you sand would get water under the
feathered edges and lift them up, so you wouldn't have a sound
surface. And then you'd have to wait for the wet wall to dry,
when it really is preferable to prime the newly exposed wood as
soon as possible.
If you just wash with moderate force before scraping, the wood
will be protected by whatever sound paint is still on the wall.
The wall won't get so soaked and won't take so long to dry. So
after sanding, just dust off the surface with rags or a blower,
and prime as soon as your wood is dry.
Q. How soon after power-washing will the
wood be dry enough to paint?
It might take a week, or it might take less than a
day. There is no standard time to wait — it depends on
the wind, the rain, the sun, how hard you sprayed the wall, the
condition of the existing paint, and so on. But a moisture
meter can give you a firm answer in every case. We use one on
every job, because it eliminates guessing and arguments. Wood
will dry out and stabilize at about a 10% to 12% moisture
content in the outdoor air, but 15% or lower is acceptable for
paint. If it's higher than 15%, moisture will be trying to get
out of the wood, and that will prevent the paint from adhering
Pin-type moisture meters (see photos, below) that sell for
around $200 are okay for rough lumber, or for areas of a trim
board that will be covered up. For about $300 you can get a
nondestructive model that doesn't make any holes in the wood
— just hold it against the surface, and it will read
the moisture content as deep as 3/4 inch into the piece. Both
types give a more accurate reading on dense hardwoods than on
softwoods like pine or cedar — softwood may read 15%
on the dial when the true moisture content is a little higher.
But the manufacturers of the devices supply charts of
correction factors, so you can interpret the moisture readings
for different types of wood.
(left) leave holes in the wood, while the
slightly more costly nondestructive type (below) can read
interior moisture 3/4 inch beneath the surface without marking
the piece. Readings from either should be interpreted for
different wood species according to charts supplied by the
Q. Are new latex paint formulas changing
the way you work?
All the popular paint brands
have been reformulated with antifreeze and coalescing agents,
so the fresh paint resists freezing and can cure in cold
weather. Just a few years ago, the minimum application
temperature for most latex coatings was 50°F, but now we
can use most exterior paints in temperatures down to
35°F. So we've lost our excuse — like the ad
for one paint said, the good news is we can paint when it's
almost freezing outside, and the bad news is, we can paint when
it's almost freezing outside.
But the new formulas make warm weather painting trickier
— that's the flip side. On a mild 75°F day,
paint tacks up and dries much faster than it used to. So in
spring or fall, when the air is cool, we paint with the sun
— we pick a wall to work on that is in the sunshine,
or at least has been in the sun very recently, so the surface
will be warm. But in summer we have to avoid the sun and work
in the shade, so the paint will flow. If you paint a wall
that's in full sun, or is still warm to the touch from recent
sunshine, you will get lots of lap marks — it's hard
to keep a wet edge when the paint dries so fast. Slower drying
is better for the paint, also — paints cure best when
they dry gradually over five or six hours.
Touch-up work is also a problem with the new formulas. You
can't be sure of getting consistent color if the weather
conditions change between the time you paint and the time you
touch up — even if you use the same pail of paint. If
we paint a wall on a 75°F day in September and come back
to touch it up on a 40°F day in October, we often notice
a visual variation.
New cold-weather paint
formulascan be used in
temperatures as cold as 35°F. But their rapid drying in
warm or hot weather may cause difficulties, and the finish
color of touch-up work done in cool weather may vary from the
color of walls painted in warmer weather using the same batch
Q. Is oil or latex primer better for old
Oil-based primers usually work
better for repainting jobs, because they cut through any
residual dust and penetrate into old wood. Dust repels water,
so water-based primers tend to bead up on a dusty surface.
However, oil-based formulas won't be an option in the future,
because new environmental rules will start to prohibit them in
2005. So down the road, we'll just have to prep and dust more
Q. We've heard of cases where people had
a lot of trouble getting paint to stick to red cedar clapboards
on brand-new buildings, even though the wood was dry and clean
and was primed and painted just a few days after it was nailed
Red cedar is our nemesis.
Builders used a lot of it during the boom years of the 1980s
and 1990s, because it comes in long lengths and goes up so
fast. But it doesn't hold paint well, because in the
manufacturing process it develops what we call a "mill glaze."
Planers in the sawmill compress the surface fibers and burnish
the "extractives" in the cedar sap into a resinous or waxy
glaze that resists penetration by primers and paints. If you
drop water on the planed face of a cedar clapboard and the
water beads up, it's got that glaze. Paint may stick to the
glaze at first, but the glaze itself is unstable —
when moisture works on it, it breaks down and the paint comes
To make paint stick to cedar, you have to get down to sound
wood: Sand the glaze off, or else cut through it by washing the
surface thoroughly with a TSP solution. You'll see the
extractives coming off: When you scrub a 10-foot section of
wall with a bucket and brush, the detergent water in your pail
will turn bright red from the compounds you're washing off the
Q. Do you need to use a moisture meter
for inside work? Is moisture a problem for inside the house as
well as outside?
A moisture meter is always
useful on a painting job, indoors or out. It's the only way to
be sure that the wood is dry enough to hold paint — a
leak or a humid environment could have left the wood close to
its saturation point. And it tells you whether your wood is
likely to shrink or expand dramatically after you paint. Wood
inside a house cycles from 12% or higher moisture content
during the hot, humid summer season down to as low as 4% or 5%
in a dry, heated house in winter, and that can cause shrinkage
of 1/4 inch across an 8-inch door panel or trim board. The
painter needs to take that movement into account.
Q. Can you paint a new house in winter if
it has no heat or only temporary heat?
For inside work, we still need
a minimum temperature of 50°F in order for the paint to
cure properly. We'd prefer it a little warmer — not
only because it's uncomfortable to paint when it's that chilly,
but also because the paints may not flow as nicely or leave as
nice a finish at 50°F as at 65°F or
Temporary heat is another matter. Sometimes we have to paint
in houses where propane heaters are running, but it doesn't
work well at all. The moisture in the burner exhaust makes the
air humid and keeps the wood from drying out. You'll get a much
better paint job if you let the permanent heating system
operate in the house for a while, monitor the indoor humidity
with a hygrometer, and check the wood moisture content with a
moisture meter until you get down to the low end of the
seasonal range. Paint will have many fewer problems down the
road if it's applied to trim that has adjusted to dry winter
conditions in a heated house.
Q. What are the big differences in the
way latex and oil paints perform?
Oil's penetrating ability is
its main advantage for repainting work. But latex has
advantages that make it a better choice for a top coat. For one
thing, latex coatings stay flexible longer, and that gives them
a longer service life. When paints fail with age, it's because
they've lost flexibility — you see alligatoring when
paint has gotten brittle and can no longer expand and contract
along with the wood (see photos, below). Latex paints take
longer to reach that point. Also, latex coatings breathe better
than oil coatings, so they are less prone to peeling: Moisture
in the wood can escape more easily, instead of getting trapped
under the coating at the surface and stressing the adhesive
bond. And finally, the acrylic colorants in latex paints hold
longer than the alkyd pigments in oil paints do. We see a lot
more fading with oil paints. So there are good reasons that
latexes tend to be preferred for top coats in general, and for
primers in cases where the superior penetration of an oil
primer isn't a significant factor.
Alligatoring occurswhen paint loses flexibility and can't
accommodate the seasonal expansion and shrinkage of wood
(left). Latex paints stay flexible longer than oil paints,
prolonging their service life. A new coat of paint applied over
tight alligatored paint (right) will perform well if the wall
has been properly prepared. The authors recommend washing to
remove dirt and mildew, scraping to remove loose alligatored
paint, sanding to feather the edges of the remaining
well-adhered paint, and dusting the sanded wall. Oil primer
should then be applied as soon as possible, followed without
delay by a latex top coat.
Q. How long can you leave bare wood
exposed before applying primer, and how long can you leave
primer exposed before painting?
The sooner you get bare wood
primed, or fresh primer painted, the better (provided the wood
is below 15% moisture content, or the primer has dried). If you
leave wood out in the sun and air for more than two weeks, the
wood fibers deteriorate and the surface begins to lose its
integrity. If wood has been exposed for a month, that degraded
surface should be sanded off to expose sound wood fibers before
primer is applied. Use 80-grit or 100-grit sandpaper —
sanding with any finer grit can actually seal the wood.
Primers also suffer if they're left exposed for too long
— 30 days is about the limit, and some suppliers will
tell you to paint within 7 to 15 days of priming. Primers are
intentionally formulated to be more porous than paint, because
that supports a strong adhesive bond with the finish paint. A
primed surface is like a lot of little fingers ready to grab on
to the top coat and interlock with it. For that same reason,
primers will get dirty if they aren't painted right away. Dust,
spores, pollen, smoke, and everything else that's in the air
collects in those sticky pores. Once the primer's dusty and
dirty, it loses its "tooth," and the top coat won't grab on to
it as well. Also, the spores in the dirt will grow out into
mold and mildew before long. Once the primer is dirty or
mildewed, you need to wash and sand the wall again, and then
prime it again, if you want your paint job to last.
Primer should be painted
overas soon as possible after
applying. Its porous "tooth," intended to provide strong
attachment for the top coat, will quickly collect dirt and
support mildew growth if left exposed to the air. Most
suppliers recommend a maximum exposure of 15 days before
Q. What's the best way to keep knots from
bleeding through paint?
Knots should be sealed with a
shellac, like B-I-N pigmented shellac from Zinsser
(732/469-8100, www.zinsser.com). More coats of shellac
work better — you'll get the best results from three
or even five coats of B-I-N. If the extra coats are giving you
too high a build, you can cut the pigmented shellac with clear
shellac and get the same protection with a thinner
If you're using pine or another softwood with a lot of sap in
the grain, it works well to prime the whole board on all sides
with a newer product from Zinsser called SealCoat. That's a
concentrated shellac that has been de-waxed, so it can be used
under any coating (unlike B-I-N and some other standard
shellacs, which may repel polyurethane and some other
coatings). If you seal the boards with SealCoat, the regular
primer coat you put on next won't soak into the wood and raise
the grain, and the primer and paint solvents won't get into the
wood and draw sap to the surface out of the knots and grain.
SealCoat dries fast, too, so using it won't slow you
Q. Do you use shellac to seal knots on
exterior trim, too?
Shellac is not an exterior
product — it has no flexibility to handle wood
expansion and contraction, and it gets lifted off the wood by
moisture. But it works on exteriors if you sandwich it between
the primer coat and the paint coat. Prime the trim first, then
seal the knots with three to five coats of shellac, then paint
over the shellac. That way, the shellac will block the sap in
knots from bleeding through and showing, and the prime coat
will protect the shellac from moisture attack.
Q. How long should you wait before
painting a fresh plaster wall?
That varies for different types
of plaster. These days, most people are using veneer plaster,
which is applied in a thin coat and dries out more quickly than
traditional three-coat plaster. But there's really no set time.
Instead of guessing — "Okay, it's been two weeks,
let's paint" — do this simple test: Take an 18-inch
square of 4-mil poly and seal all four edges to the wall with
duct tape. If the plaster is still moist, you'll see moisture
beading up on the back of the poly. If you don't get moisture,
the wall is ready to paint.
But you should also check the chemistry of fresh plaster
before you paint it. Lime-based plasters are alkaline when
they're first applied and gradually neutralize as they cure.
For painting, you want the pH level to be close to neutral, say
between pH 5 and pH 8 (a pH of 7 is neutral; 5 is more acidic,
and 8 is more alkaline). You test that by dampening the plaster
surface and touching a piece of litmus paper to it. The litmus
paper will change color in response to the pH of the damp
plaster, and you read the pH by comparing the paper's color to
a reference chart. If the plaster is still too alkaline, you
have to wait a little longer. If you're in a hurry, you can
wash it down with a diluted solution of vinegar (which is an
acid) to get it to a neutral reading. But there is no set time
to wait for the proper pH, anymore than for the proper moisture
content. The only way to know is to test.
Q. How do you deal with panel shrinkage
when painting wood doors?
If you paint a door in summer,
you'll often see exposed wood the following winter at panel
edges (see photo, below). Masonite or other composite doors
don't have this problem, but the only way to prevent it on a
solid wood door is to paint the panels before the door is
assembled, and that's not going to happen except on the
occasional high-end custom job. If the customers want wood
doors painted in summer, we warn them that the painter will
probably have to come back and touch up the paint, and we
charge for that as an extra.
Shrinkage of wood panelsin winter's dry indoor air can reveal
unpainted edges on wood door panels or on raised-panel or
beadboard wall surfaces, almost guaranteeing callbacks for jobs
done during the humid months of summer.
These touch-ups are trickier when the coating is a clear
finish over stained or natural wood, especially if the finish
is spray applied. The wet finish tends to creep into the dado
and dry as a little thickened ridge. On the callback, that
ridge has to be sanded smooth, and then the touch-up stain and
finish have to be blended in carefully.
You also get shrinkage that exposes unpainted wood on paneling
such as beadboard. But you can preprime or even prepaint those
pieces before installing them, so the shrinkage won't expose
any uncoated wood.
Shrinkage can also make a caulked joint look terrible in six
months, even though it looked fine when the job was done. When
the wood shrinks, the caulk pulls off and splits with an ugly
Charles Gilley Jr.is owner of Restoration Painting of South
Woodstock, Vt., and has 30 years of experience in the
field.Charles Owensis president of Two Dogs Painting, Inc.,
and has 17 years of experience in the painting