SW - Art DIR ExtStain Prep

Before you apply stain, make sure the surface is clean (no dust, dirt, wood fibers or grease), dry and free from mildew. When a surface is not clean, stains and other finishes have trouble sticking and may end up peeling.

You can remove dirt with warm water and detergent, but mildew problems require more. Removing mild mildew requires a mixture of one quart household bleach in three quarts of water.

  • Wear rubber gloves, long sleeves, and eye protection and quickly wash off any solution that touches your skin.
  • Rinse well with a hose, then let all surfaces dry thoroughly before you begin staining.

Untreated, New Wood

For untreated exterior wood surfaces, stain shortly after installation to help prevent wood deterioration, darkening or mildew growth — a common result of exposure to the elements.
Note:  Be careful not to stain treated (green) wood until it has had a chance to "leach out" or weather. Ask an expert at Sherwin-Williams or at the lumber company where you bought the wood when the best time is to apply the stain.

Old Wood

For previously stained or painted surfaces in need of a solid color stain, be sure to remove all dust, dirt, loose and peeling paint and chalk deposits before getting started. (If you're applying WoodScapes semi-transparent stain to any previously painted surfaces, it's essential to first sand or scrape down to the bare wood.)
To sand wood smooth:

  • Use a medium grit paper at first. You can use coarse sandpaper on rough wood surfaces.
  • Finish the job with a fine grit paper to ensure the smoothest texture.
  • Be sure to use a protective dust mask.

Warning! Removal of old paint by sanding, scraping or other means may generate dust or fumes that contain lead. Exposure to lead dust or fumes may cause brain damage or other adverse health effects, especially in children or pregnant women. Controlling exposure to lead or other hazardous substances requires the use of proper protective equipment, such as a properly fitted respirator (NIOSH approved) and proper containment and cleanup. For more information, call (in the U.S.) the National Lead Information Center at 1-800-424-LEAD or contact your local health authority.


  • Replace any badly rotted boards.
  • Caulk around windows and doors to create a proper seal.
  • Check the wood's surface for any surface irregularities (cracks or holes) that need smoothing out with wood filler.
  • Remove as many items as you can (planters, mailboxes, shutters, house numbers, etc.).
  • Spread out a drop cloth to protect your foundation, walkways, shrubs, planters and other yard items from accidental spills.

How much stain will I need?

To calculate how many gallons of product you will need, all you need is a tape measure and some simple math.

  1. Below the Roofline - Measure the distance along each side of your home. Multiply that number by the height up to the roof line.
  2. Above the roofline - Measure how many feet the tallest point of the peak rises above the side height measured in Step 1 and multiply that number by 1/2 the width of that wall. Add this figure to the total you calculated in Step 1.
  3. Windows and Doors - Determine the area of all windows and doors using the same width x height calculations and subtract each from your total.
  4. Total - Divide the total area by the square feet one gallon will cover (200 if you have rough siding and 300 for smooth siding).
  5. Trim - Multiply the number of doors by 21, the number of windows by 15 and add up the results. Divide by 200 (if you have rough trim) or 300 (if you have smooth trim).
The Right Tools

See Also:

SW - ArtDIR ExStnPrpBd1

WOODSCAPES® Exterior House Stains

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