Introduction: The basic rule
for when you need a paint primer is if the surface
your painting is not totally flat or if the
materila is raw wood. If it is raw wood or does not
a flat surface you
should always use a primer.
Surfaces with cracks,
holes or depressions that aren’t properly sealed
could greatly reduce the paint’s ability to bond
effectively. Porous material such as wood, drywall
and concrete tend to come with primer
recommendations attached. The natural imperfections
or holes in such materials can create an uneven
surface for painting. Each of these different
materials requires a somewhat different care and
generally always need a paint primer.
Wood is the most
common surface for paint primers, a fact that is
hardly surprising considering its organic nature.
The reason you always want to prime wood before
painting is twofold:
To protect the
paint
To protect the
wood
A number of modern
paints dry into proper color and hardness via
evaporation, meaning they require the water to find
its way into the atmosphere. The problem is that
wood is a notoriously thirsty substance, and it is
easy for water to get absorbed into the grain
itself. Often the paint will begin to pucker and
peel if the wood isn’t dry, making it necessary to
scrape and start over. Paint primer creates a
watertight seal between the two and ensures the
paint has a smooth and adhesive surface with which
to bond.
The second reason
you always want to prime a wood surface is because
the same absorption can quickly undo your attempts
at an even coat. Lighter paint colors especially
will often reveal imperfections in wood grain even
after several passes, requiring you to paint over
and over for a truly solid hue. Although you can
apply paint repeatedly to achieve the same effect,
a fast coat of primer first will save you time and
money.
The wood itself can
be injured without a primer in place. Although a
negligible amount of water is absorbed during
drying, greater amounts may leech into the grain if
that painted surface is exposed to the elements.
Without the use of a primer it’s not unusual for
repeated rain storms to take their toll, creating
devastating conditions for mold, mildew and
warping. Although many people consider outdoor
paints to be waterproof, often they are not because
their hardy nature derives from their ability to
absorb rainwater with ease.
Paint primer is
recommended for a variety of other materials too.
In concrete and drywall, for instance, you simply
want to seal the surface and create a solid bond
without having to worry about similar problems with
drying and moisture.
For metals,
especially those prone to rust, a paint primer can
protect the surface itself and keep moisture locked
out avoiding rust and pealing. Porous plastics can
benefit from a coat of primer or if you are putting
a light color over a darker color.
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