Choosing Paint for Wood Exteriors
Specific Prep, Primer and Paint Steps for Various Conditions
Sep 29, 2009
The exterior of a house takes a lot of abuse. It is pelted with rain, frozen by snow, sleet and ice, and baked with the hot sun. Exterior wood portions of the house, such as clapboard siding, trim and window sills, require protection from the elements. When the surface is prepared properly and thorough consideration is given to the kind and quality of paint that is to be applied, the reward will be a long-lasting quality appearance.
New and Old Surfaces
For new wood surfaces that have not been previously painted, coat the exterior with a latex (water-based) primer and then top coat with a quality latex house paint. The blister resistant properties of latex make it perfect for this application.
For previously painted surfaces where the surface is free of peeling, cracking, flaking or mildew, apply two coats of quality latex or oil-based paint. If the surface has a previous coat of latex, a new coat of latex can be applied. For surfaces that contain oil-based paint, either cover with another coat of oil-based paint or apply a quality primer before covering with a latex coat. Surfaces that have damage, especially those on older homes, require special treatment.
Paint Cracking and Flaking
Cracking and flaking are caused by stress applied to the paint film that is greater than the strength of the paint. This develops when the surface expands or contracts due to the changes in weather conditions. Larger cracks will cause paint flaking.
To correct this situation, remove all flaking paint with a scraper. Sand all areas smooth with quality sandpaper. Don’t forget to use proper eye protection and respirators.
Damage that has been localized to one or several small sections can be spot-primed with a latex primer. If the damage is wider, apply a full coat of primer to the entire area. Finish the job with a top coat of quality latex or oil paint. If the damage is extensive, the wood might first need to be replaced before proceeding with painting.
Peeling is caused by excess moisture buildup that moves to the surface when the sun heats the area. Find the sources of excess moisture (dripping gutters, standing water in dirt around a foundation, too much shade that keeps areas damp) and correct the problem before repairing the wood surface. Then, scrape all peeling paint and sand. Apply a latex primer. Finish with a top coat of quality latex or oil paint.
One additional step can include the application of a water protection sealer to the wood. Do this with a brush or roller after the scraping, sanding and other preparation steps but before applying the primer. The same kind of sealers used for wood decks can be used on other outdoor wood surfaces.
Surfaces with Checking and Crumbling
Checking and crumbling are caused by temperature changes. Checking occurs when top coats show fine breaks without penetration to the wood surface. One cause is improper prepping of the surface. Crumbling results when moisture penetrates into the tiny cracks, causing small particles of the paint to lose adhesion and fall away.
Remove damaged paint and sand smooth. Apply one coat of latex primer followed by one top coat of quality latex or oil.
To learn more about painting exterior surfaces, take a look at the House Painting How to Manual.
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