If you go into a paint store
and ask how to protect wood
from the weather, you'll probably
hear this answer: Use an
oil-based primer, and top it
with one or two coats of premium
latex paint. It's widely
believed that oil-based
primers give the best protection
from moisture, because
they penetrate the wood more
easily.
But testing at the U.S.
Department of Agriculture's
Forest Products Laboratory
(FPL), in Madison, Wis.,
shows that this conventional
wisdom may be wrong. FPL
scientists say that, while oil
primers and paints adhere
well to wood and create the
best shield against rain and
humidity, the resins in oilbased
finishes lose their flexibility
over time. No matter
how well the surface is sealed,
the wood moves in response
to humidity and