How to Choose Primer for Exterior Wood
Proper preparation of exterior surfaces is critical to a long-lasting paint job, especially for wood. Not only is choosing a high-quality paint important, but picking the right primer is just as, if not more important. Using the right primer can double the duration of your paint job. There are quite a few primer choices: All-purpose latex primer, acrylic exterior primer, oil-based primer, shellac primer and breathable, oil-based primer. Choose the right one. Does this Spark an idea?
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Instructions
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Pick a high-quality acrylic for most exterior wood in reasonably good shape. It remains elastic and permeable so moisture can "breathe" through the paint skin. This will decrease the chance of the paint bubbling and peeling due to moisture in the walls.
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Consider oil- or shellac-based primers for cedar or redwood. Factor in problems with tannin staining. Tannin is a natural substance in the wood, which will bleed through and cause yellow or brown stains in your finished paint job. It is water soluble, so it will bleed through any water-based product. Use oil and shellac primers to stop tannin from bleeding through. Some water-based primers claim to be able to stop tannin staining, although sometimes two or more coats will be necessary.
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Ask at your paint store about breathable oil primers, which allow passage of moisture from the house through the paint. (All water-based products, unless they are sold specifically as moisture-barriers, are breathable.) Choose breathable oil primers to help combat tannin staining from some plywood materials, in addition to cedar, redwood.
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Use oil-based primers for very soft older wood. Oil-based primers penetrate much deeper into the wood fibers and create a more solid substrate to paint over.
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Tips & Warnings
Do not wait longer than 30 days between priming and painting. The longer the primer sits uncovered, the more grime it can accumulate and the harder it gets, decreasing its ability to bond well with the topcoat.
Shellac-type primers don't hold up well outside in any area where they are exposed to weather, like windowsills or south-facing siding and trim.
Oil-based primers are messier to use, harder to clean up and most people dislike using them.
References
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