Learn How To Prepare Wood For Exterior Painting

Nature puts on a fresh coat of color this time of year. Isn’t it time you did? Maybe the outside of your house is looking a little too weather-beaten. Or perhaps you have tired of the color of your den. Summer’s dry weather affords the best opportunity for painting projects.

This article provides details about wood surface preparationbefore paint or stain application in order to assure a successful job.

A successful paint or stain job means that the result looks good and is durable.

1. The following recommendations are made below

Make Sure of Proper Wood Moisture Content Before Painting

Never paint wood with a moisture content over 20%. Ideally, the wood should be painted at its average moisture content for that climate – about 12% for most of the United States, 9% for dry southwestern states.

2. New Wood Surface Preparation For Painting

A rough-sawn wood surface will hold paint and stain much longer than a smooth, planed surface, which is why many contractors prefer to install siding rough side out. Also most lumber and siding today is flat-grained, which holds paint less well than vertical (or edge) grained.

3. Wood Species and Wood Grain Affect Paint Success

In general, less dense woods hold paint better than more dense woods. . Also, within a single species, vertical-grain (also called edge-grain) wood holds paint much better than the more common flat-sawn lumber, primarily because flat sawn wood shrinks and swells more from changes in relative humidity.

4. Clean the Wood Surface Before Application of Paints / Stains

The best paint in the world can fail within the first year if applied over a wet, dirty, or degraded substrate. So the first priority is to make sure that the material being painted is sufficiently dry and clean.

5. Temperature and Time of Day Impact on Paint Job Success

Oil-based paints should be applied when it is over 40°F; for latex coatings the temperature should be at least 50°F during application and for 24 hours after. Also it is best not to apply paint too early or too late in the day. If the dew has not evaporated in the morning, both oil and latex may have adhesion problems. If applied within two hours of sunset and a heavy dew forms before the paint dries, latex paints may streak and oil-based paints may not cure properly.

6. Importance of Priming New Wood Before Painting or Staining

All paints and most solid stains require priming on new wood. Primers are formulated with a higher ratio of binder to pigment than paints. [This means that there is more binder and less pigment in a primer than in a finish-coat of paint – Ed.] The primer forms a durable film that bonds well to the surface and blocks water.

7. Use a Paint or Stain Primer Compatible with the Paint or Stain Top Coat

Be sure that the primer you select for your paint job is compatible with the type of coating you intend to use for the top-coat. Read the manufacturer’s label-instructions and check with your paint supplier. Painting some top coats atop the wrong primer is a guarantee of a failed paint job that shows up as wrinkling, cracking, or loss of adhesion of the building coating.

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