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Surface Preparation Prior To Staining of
Residential Wood Siding

This article and graphics supplied courtesy Cabot Stains

The beauty and durability of any stain job depend on both the quality of the stain and proper surface preparation. Just as you wouldn't wax a car without washing it first, you shouldn't stain a house without cleaning it first.

Homeowners often spend hours choosing just the right stain product and color, yet give little or no thought to surface preparation. Professionals know, however, that proper preparation ensures a long lasting stain application and eliminates many problems before they start. For the Do-It-Yourselfer, follow these steps to properly prepare a wood surface for coating:

Close Visual Examination

Look for problem areas and obvious construction defects. The surface should be in a good, sound condition and wood should not be eroding, rotting or decaying. Then check for surface contaminants such as mildew stains, cedar bleed, dirt and chalkiness. You must remove such contaminants before applying the stain, but remember – there is no single cure for every surface problem.

Testing the Surface

Testing the souindness of a paint surface with tape

To ensure wood is ready to be stained, always perform a tape test. First, press a piece of tape firmly against the surface to be stained, then tear it away and examine the back. The presence of old stain or loose wood fibers on the tape could indicate a potential moisture problem. Because excessive moisture entering the wood accounts for many problems, such as peeling, premature wood erosion, rot or decay, the surface must be dry at the time of staining, with a moisture reading of 15 percent or less.

Also, the surface must be situated so as not to absorb or collect excessive moisture after staining. A solid-bodied stain or paint will not peel unless moisture forces it off the surface. Other surface problems, such as premature erosion of the wood, may result from neglect or severe weather exposure. Before staining, replace rotting or decayed wood and remove loose stain and eroded wood fibers by sanding, scraping or power washing the problem surfaces.

Dealing with Surface Contaminants

Once the surface is in good condition, re-inspect for dirt, mildew stains, cedar bleed, chalkiness and other foreign substances. It is important to identify each type of contaminant, as each requires its own treatment. Mildew stains, dirt, soot and other pollutants often appear as black dots or specks on the surface.

To determine the correct treatment, apply a small amount of fresh household bleach to these black areas. If the dark discoloration lightens quickly, mildew stains are present. Dirt, soot and other pollutants will not change color but may simply move within the bleach solution.

Eliminating Mildew Stains and Dirt

For the most effective removal of mildew stains, dirt, soot and other pollutants, use a cleaning solution that contains sodium hypochlorite (active ingredient in household bleach), sodium metasilicate (non-ammoniated detergent/wetting agent), and calcium hypochlorite (strong oxidizing agent) such as Cabot Problem-Solver Cleaner. All three ingredients are important because each has a specific function in the proper cleaning of the substrate.

Chalkiness

Chalkiness may be detected by rubbing your hand or a clean cloth over the wood surface. If you detect flakiness on your hand or cloth, the previous stain application is breaking down and causing the chalking. Prior to any reapplication, remove the chalkiness with a detergent wash that includes sodium metasilicate. Again, Cabot Problem-Solver Cleaner is a good option.

Cedar Bleed

Uneven stain appearance caused by cedar bleedCedar bleed (tannic acid) is reddish brown discoloration that may make old stain applications appear blotchy or uneven. Test for it by applying a ferrous sulfate solution to the discolored surface. If the solution turns from its natural color to blue-black, the wood has been affected by cedar bleed. Ferrous sulfate is not commonly available at retail, but homeowners can call Cabot's Technical Services & Support for assistance (1-800-US-STAIN). An oxalic acid based solution like Cabot Problem-Solver Brightener will effectively remove the discoloration and is readily available. It also removes nail and metal rust stains.

Furthermore, Cabot Problem-Solver Primer is recommended for use on extractive-prone wood species such as red cedar, redwood, mahogany and fir. It is also excellent when applied to pine, cypress, spruce, and even pressure-treated wood. This product has exceptional adhesive properties and can be applied immediately to new, dry, unseasoned, mill-glazed (smooth) siding.

Pressure Washing? Very effective, but be very careful!

If the thought of scraping and sanding loose peeling stain is daunting, consider renting a pressure washer from your local home improvement store. While the pressure washer is not always a cure-all (there are occasions when scraping and sanding may be necessary), using the right pressure washer and technique will tackle most jobs with ease. For general cleaning on wood, a tip of 40 degrees and 500 psi (pounds per square inch) is adequate. A higher psi can produce poor results and damage your wood. Below are a few pointers to consider especially for siding:

On siding, always wash from the bottom up and rinse from the top down. Keep the nozzle or tip at least 8-10 inches away from the surface and perpendicular to the siding to avoid forcing water behind siding. While holding the tip perpendicular to the siding, it may be tilted at a slight angle to the siding to allow the pressure stream to get under loose stain and lift it off. Close all windows and do not use the pressure washer on the windows as damage may result. Do not spray directly at or into light fixtures, electrical outlets, gable-end vents, crawl spaces or open eaves. Refrain from using a pressure washer on a windy day to avoid damage related to overspray. After washing give the surface two to three days to dry.

While cumbersome, proper surface preparation guarantees a quality stain job. Identify what the problems are and address them before you open a can of stain.

Visit the Cabot Stains website to find the right stain and preparation products for your
exterior interior wood surfaces... plus a list of your local retailers!

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