| Okay,
let’s be honest. Do you know when you should prime
before you paint? You’re not sure? Well don’t
feel too bad about it; you have plenty of company.
There are few painting issues that cause more confusion
than the question of whether or not to use a primer
. Fortunately, an understanding of the role that primers
play helps clarify matters.
In a nutshell, the basic function of primers is to overcome
problems in the surface you’re painting. If every
surface were perfectly suitable for painting, primers
would not be necessary. Unfortunately, such is often
not the case. Some surfaces pose adhesion problems;
others are porous; still others are discolored or stained.
Some substrates have surface defects that make them
uneven or contain substances that can migrate or “bleed”
through a paint to the surface. Ferrous metal materials
(iron or steel) are vulnerable to corrosion.
Primers are designed to address all of these problems.
They form thick films that adhere well to all types
of surfaces. They fill in pores and irregularities,
cover blemishes, and can be formulated to block staining
materials. When made with reactive pigments, they effectively
protect against corrosion of ferrous metals.
 So,
when should you prime? Any time you don’t
have a sound surface.
Generally speaking, the only substrates that normally
don’t require priming are previously applied paints
in good condition (no cracks, flakes, or exposed substrates).
Virtually all other common architectural surfaces—new
and weathered wood, masonry, metals—should be
primed before painting. Moreover, even existing paints
in good shape should be primed if they are very glossy
or chalky. As a general rule, if you have any doubts
about the surface you want to paint, use a primer to
avoid any potential risk.
For best results, choose an appropriate primer for the
surface you are painting.
Oil-based primers have been around for many years and
are still used frequently in interior applications where
stain-blocking is a priority. The newer high-quality
acrylic latex primers have proven to be excellent performance
alternatives in many applications: weathered wood and
exterior surfaces in particular. Metal substrates typically
require primers containing rust-inhibiting pigments.
These are known as ‘Anti Corrosive Primers’.
For more information, check out our exterior Primer
on Primers
(pdf) found in our Steps
to Success for Selecting the Right Paint of Exteriors
.
As always, the professionals at your local paint store
can be a great help in choosing the right primer for
your paint project.
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