How to Select an Exterior Paint Primer

When trying to select an exterior paint primer, choose oil-based (alkyd) primer for cedar or redwood to seal in the tannin stains inherent in these woods. If an oil-based primer isn't practical, look for a water-based primer capable of blocking tannin stains. Be prepared to apply two coats of water-based primer because it's not as effective for blocking stains.

Use alkyd primer for priming over anything that has been previously painted with an oil-based paint. Water-based primers and paints will not adhere well to oil-based paint, but can be painted over oil-based primer.

Choose an alkyd rust-inhibiting metal primer for iron or steel. If after scraping and wire-brushing there's still rust on the surface, pre-treat it with rust inhibitor. This is available in spray cans or in a brush-on formula.

Use alkyd primer for aluminum siding and any chalky surface. To test for chalk, run your hand over an exposed area of siding. If a white residue comes off on your hand, this needs to be power-washed or scrubbed off, and primed before painting.

Select an acrylic (water-based) primer for the following surfaces: Masonry (including brick, stucco or cinder block), plywood, composite siding, and galvanized steel.

Ask for recommendations for an appropriate bonding primer for very hard, slick surfaces like some plastics and vinyl trim.

Paint a thin coat of "peel stopping" sealer over layers of old paint once you've scraped, pressure-sprayed and/or sanded off as much as you can. This sealer slows further peeling, but does need to be primed for maximum durability.

Skip priming on some surfaces when using a quality 100 percent acrylic paint, if indicated on the label directions. These surfaces include vinyl siding and shutters, and some masonry if in sound, clean condition.