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Preparing Wood Siding for Painting

Proper preparation is key to painting wood siding successfully. If the existing siding is in good shape, the only preparation necessary may be thoroughly washing it. But if the existing paint is cracked and peeling, you’ll need to remove it to a point where the surface is flat, smooth, and free of the old, failing paint.

When hosing down the siding, be careful not to force water into the joints between siding boards. In some cases, you can use a power washer to clean the surface, but, if you do this, be very careful not to drive water into the wood or the joints between siding boards, and don’t erode the wood’s surface with the powerful blast. (Washing alone is often not enough to remove mold or mildew from the surface. For more about dealing with this, see How to Remove Mildew From Siding.)

Power sanders can be used to smooth the edges of scraped areas or to clear an entire surface of paint. For big jobs, such as sanding down an entire home’s siding, a commercial-grade, 7-inch sander works best. You can buy one at a home improvement center or rent one from an equipment rental company.

Sanding is accomplished in two stages. First, the paint cover is completely removed with coarse sandpaper-60-grit is recommended. This will leave cuts in the wood, so these must be smoothed with medium sandpaper (100-grit).

Sanding is a meticulous process that requires the following precautions:

• Make sure the sander is running at full speed before touching the wheel to the surface.

• As you bring the sander into contact with the wall, lean on the tool slightly until you hear the motor slow, and then keep moving it along the surface so you do not gouge the wood.

• Keep the sanding wheel at a slight angle (5 to 10 degrees) to the wall; otherwise, the wheel will spin out of control across the surface.

• Discard sanding disks as they become clogged with paint; otherwise, they will actually burn the surface.

• Do not use a power sander in the rain.

To scrape small areas of peeling paint, a paint scraper, putty knife, or molding scraper is sufficient. If you are using a power sander to remove an entire finish, use these tools to scrape areas that the sanding wheel cannot reach, such as corners and other tight spots.

To be sure you loosen as much paint as possible, scrape areas of loose paint from every direction; sometimes old paint that’s scraped from left to right seems solid but comes off easily when scraped in the opposite direction or up and down.

Place two hands on the scraper and keep it flat to avoid gouging the wood. If you do happen to create gouge marks, sand them down or fill them with a vinyl exterior spackling compound so they will not show through the new paint job.

If the paint that remains after scraping has high or rough edges, sand, or “feather,” them with coarse sandpaper to make them less noticeable.

Damaged sections of siding will need to be repaired or replaced. (For more about repairing wood siding, see How to Repair Wood Siding.)

Upon completing the steps shown here, dust off the sawdust and caulk any open seams. Prime any bare wood with a latex primer that is tinted toward the finish color, and allow the primer to dry thoroughly before starting to paint.

1. Scrub surface with stiff-bristle brush


1Hose down the siding, and then scrub it with a stiff-bristle brush mounted on a pole. Clean the area with a solution of water and tri-sodium phosphate (TSP). Because this solution is caustic, do not use it on bare wood, and always wear rubber gloves and safety goggles when using it.


2. Scrape and sand the siding


2Scrape any loose paint, and use a power sander to remove large areas of paint. When using a sander, work in 3-foot sections at a time. Move the sander horizontally across the top of a board, in a wave-like pattern across the middle, and horizontally along the underside of the lip.


3. Fill holes and gouges


3Fill any holes or deep gouges, using a putty knife to apply vinyl exterior spackling compound. (Use a matching wood-toned filler if you intend to apply a semi-transparent stain.) Allow the spackling compound to dry.


4. Sand until smooth


4Use a sanding block or a palm sander with 100-grit sandpaper to sand each patch until it is smooth. Finally, sweep away residual dust and scrapings.

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