Guide to Successful Exterior  
Painting  

Older buildings have usually been painted with oil-based paints. Newer oil-based paints, however, do not have the longevity they once had because they are no longer allowed to be manufactured with lead. Available latex paints are excellent, but the transition from having oil-based paint on a house to having a latex coating requires careful preparation. Anything less can cause frustration and concern that the new paints "just won't stick." Once accomplished correctly, however, the painting cycle need not be any more difficult than when lead-based paints were available. 

To provide definitive information on successfully painting a house, Forest Products Laboratory (FPL), in Madison, Wisconsin, has worked in conjunction with the U.S. Department of Agriculture and the University of Wisconsin to study various aspects of wood. One of their projects included testing different combinations of paint and primer by exposing them to ten Wisconsin winters. Their conclusions are outlined below as a recipe for a ten year paint job. 

Not surprisingly, FPL found that most paint failure was due to moisture penetration under the paint surface. Moisture penetration, however, can usually be effectively addressed through application of an oil base primer over water repellant wood preservative followed by careful caulking. Two coats of latex paint completes the job. If the surface preparation has also been properly done, then repainting in eight to ten years will be much easier to accomplish. 

Of all the steps listed below, surface preparation cannot be overemphasized. Paint simply will not stick to dirty, flaking surfaces. 

Equipment and Materials  

Hand held scraper, those with an approximate 45 degree angle give better leverage. Choose scrapers with replaceable blades. 

Extra blades for scraper. 

Metal file for sharpening dull scraper blades. 

Sandpaper or other abrasive material. 

Trisodium phosphate detergent (available at hardware stores). 

Household bleach (used to eliminate mildew problems). 

Sturdy nylon bristle scrub brush (natural bristle will be eaten away). 

Bucket. 

Rubber gloves, face mask and safety glasses. 

Assorted brushes (traditional 6 inch brush is used for wood siding). 

Water repellent wood preservative (make sure it is paintable). Try to obtain a product with paraffin and pentachlorphenol. 

Good quality exterior alkyd oil based primer containing titanium dioxide. 

Exterior latex caulk with silicone (cartridge and caulk gun). Use caulk with at least a 25-year life expectancy. 

Good quality exterior acrylic latex paint in the finish you prefer. Avoid paints containing zinc oxide pigments. Breakdownof these pigments is a major cause of cross grain cracking. 

The Painting Process  

Remove all loose, cracked, grazed, and peeling paint using a handheld scraper. A face mask helps protect from any lead paintdust. 

Feather the edges of any paint patches remaining using sandpaper or other abrasive material. Use a face mask. 

Scrub the scraped and sanded siding with a solution of 1 quart bleach, 1 cup trisodium phosphate, and 3 quarts warm water. Use rubber gloves. 

Rinse all traces of detergent from the wood with a garden hose. 

Allow to dry at least 2 days. 

Apply a coat of paintable water repellent wood preservative to all areas of bare wood that collect water, especially window sills, and allow to dry for 2 days. Use gloves, face mask, and safety glasses. 

Prime the clean dry surface with an oil based primer, described above. Use a brush and do not apply too thinly (400 SF per gallon). Follow the sun as you paint. Do not prime a cool wall that will later be heated by the sun, as it may blister. 

Prime over remaining paint as well as this helps the latex coats to adhere better. Do not paint in the evening on spring and fall days when heavy dews may fall. Do not paint if the overnight temperature will fall below 50 degrees. 
 Caulk all joints, sills, cracks, places where siding meets trim, nail holes (you may wish to countersink nails) and any other places where water may enter. 

Paint two (2) finish coats of latex using a brush. Follow directions on both the primer and the latex can labels for information on when to recoat. Do not wait more than 2 weeks between primer and latex coats. 

HELPFUL HINTS: 

* Place primer brush in an air tight plastic bag and place in freezer overnight, to avoid cleaning everyday. 

* When your paint job looks old and dirty, repainting may not necessarily be required. Try scrubbing your building first with the cleaning solution described in this recipe.