nailing primed trim to wall before painting
Photo: Ryan Benyi
Q: The most effective way to prime, install, and paint moldings

A: Q: I've noticed in most This Old House projects that the trim and millwork are installed primed but unpainted. Wouldn't it be easier to paint the trim first, install it, then touch it up if necessary after installation?

— Benny, Knoxville, TN

Tom Silva replies: Touchups always show, so that's not really the best approach to take. To save time, sometimes we'll install trim that's been primed and painted with one coat, then fill holes and sand lightly before putting on a finish coat with the trim in place. This works nicely for both interior and exterior work.

But if painting isn't practical, we'll make sure to at least prime exterior trim on all sides before installing it. Back-priming, as it's called, helps keep the wood from taking on water, which minimizes expansion and contraction and prevents moisture from migrating through the wood. Both will cause paint to peel. Back-priming takes a little more time at the start of a job but saves a lot of work in the long run.
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