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Forest Products

Repainting Exterior Wood

Paint on outside wood normally erodes away gradually due to the action of sunlight and moisture. A good paint job on a high quality wood surface should last eight to ten years. Unfortunately, in many situations, people end up scraping, sanding, and repainting much more frequently. 

Several factors may cause early paint failure. The most frequent cause is moisture that has penetrated into the wood. The source could either be outside rain or it could be water vapor migrating from the interior of a heated building. Other factors that could cause abnormal exterior paint problems on wood include inadequate cleaning of the surface before painting, waiting too long between successive coats of paint, painting too frequently, or poor quality paint. 

Reduce Potential Moisture Problems
The first step required to promote satisfactory performance when repainting is to reduce potential moisture problems both from outside liquid water and interior water vapor. Sealing the exterior and interior surfaces is essential; caulking joints, creating a vapor retarder on the interior, venting unheated attics, covering the ground in crawl spaces, and providing good drainage away from the structure is recommended. 

Properly Prepare the Wood Surface
The second important step is to properly prepare the surface to be painted. The wood must be clean and dry and free of all loose, peeling paint. Use a scraper and then sand the surfaces; scrub the surfaces and use caulk in any joints. 

Properly Prime Any Bare Wood Surfaces
The third step is to properly prime any bare wood surfaces. Use a high-quality primer that seals the surface; apply sufficient primer so that the grain of the wood can not be seen. A brush is the preferred method for applying all coats of paint on exterior wood surfaces. 

Use Two Topcoats
The final step involves applying two coats of a high quality topcoat paint. Acrylic latex formulations perform very well on exterior wood; purchase top-of-the-line products from a reputable manufacturer. A primer and two topcoats may provide twice the service life or a primer and one topcoat. Apply exterior latex paints when the outside temperature is between 50 and 90 degrees F.