Proper preparation is key to painting 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. The steps below will show you the basics of preparation.

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.

Damaged sections of siding will need to be repaired or replaced. For more about repairing siding, see Wood Siding Repairs.

Upon completing the steps shown here, dust off 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.

1) Begin by hosing down the siding, and then scrubbing it with a stiff-bristle brush mounted on a broomstick-type pole. Clean the area with a solution of water and trisodium phosphate (TSP) or a nonphosphate substitute, following label directions. Because this solution is caustic, do not use it on bare wood, and wear rubber gloves and safety goggles.
2) Scrape loose paint, and, if necessary, use a power sander to remove large areas of paint or to smooth any roughly scraped surfaces. When using a sander, work in 3-foot sections at a time. Move horizontally across the top of a board, in a wave-like pattern across the middle, and then along the underside of the lip.
3) Fill 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 semitransparent stain.) Allow the spackling compound to dry.
4) Use 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.