A.Bill Feist, a former
wood-finishes researcher with the Forest Products
Laboratory in Madison, Wis., and co-author of
Finishes for Exterior Wood, responds: Many
light-colored woods like fir can be self-primed
(using the top coat as the first coat) with no
problem. I wouldn't anticipate any adhesion
problems as long as the original wood surface was
properly prepared, and sunlight should not be a
problem, as the acrylics are the very best resins
for protection against UV degradation.
But if the door were to be fully exposed
outdoors, you would need the benefit of a proper
primer first coat (one recommended by the paint
manufacturer for exteriors); in that case, I'd
recommend that you strip the door and start
In general, primers should be used whether the
top coat is an oil-based or a latex-based paint,
because they're formulated to have better
penetration, adhesion, and water resistance than
either type of top-coat paint.
A good exterior primer will seal in or tie up
wood extractives so that they won't bleed through
the top coat; since it's nonporous, it will also
inhibit the penetration of rain or dew into the
wood surfaces, helping to reduce the tendency of
wood to shrink and swell.
When used on woods like redwood and western red
cedar, oil-based, solvent-based exterior primers
tend to have better tannin-stain-blocking
properties than water-borne primers.
Water-based exterior primers are generally
preferred for use on pine, Douglas fir, and most
plywoods, because they are more flexible than
solvent-based primers and are better able to
withstand the dimensional changes of those wood
When primer is applied, be sure to follow the
application rates recommended by the manufacturer.
Use enough primer that the wood grain is obscured,
but don't spread it too thick or too thin. A primer
coat that is uniform, flexible, and of the proper
thickness will distribute the swelling stresses
that develop in wood and thus help prevent
premature paint failure.