DEAR TIM: I intend to paint the exterior of my wood house soon. I am confused about using primers. Is it a good idea to use a pressure washer on my house? Do I have to prime the entire house before I apply the finish paint? What can I do to maximize the life of this new paint job? Stephanie S., Athens, OH
DEAR STEPHANIE: I am not surprised that you are confused about primers. It seems like I get a different answer to each primer, paint and surface preparation question that I ask when I talk with paint salespeople. Fortunately the entire exterior painting process is fairly straightforward.
The largest obstacle you face is the one of instant gratification. I find that most homeowners and painters want to get the finish paint on the surface as quickly as possible so that they can "see" results. If you succumb to this temptation you can rob yourself of possibly 50 percent of the life span of your paint job. Surface preparation and the correct use of primers is essential to the performance of an exterior paint job. They also consume the most time.
The first thing I want you to do is to read the label on the can of your finish paint. I'll bet that you will find a sentence that contains the following sentence or phrase, "Apply paint to a clean, dry surface." How do you wash yourself each day? Do you just stand in the shower and let the water run over your body? My guess is that you use soap and rub it into your skin and then rinse it off. This is exactly what you are going to do with your house.
Pressure washing a house, in my opinion, is not a good idea. This method does not completely clean the surface. You can demonstrate this by using a pressure washer at a drive-in car wash. After using one there will still be a fine film of deep-set dirt on your car's finish. The same is true on a house. What's more, pressure washers used in the hands of a rookie can cause significant damage to wood. It can erode wood fibers and drive water deep into exposed soft woods. Water sprayed up under siding or into cracks between siding and trim can actually saturate the back side of the wood on your house and promote rapid peeling of the fresh paint.
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Oil based primers are superb products. These products penetrate deeper into wood fibers. Oil primers also do a great job of sealing woods like cedar and redwood that can produce bleed stains when coated with water based products. Primers are a must on bare wood and previously painted surfaces that have bad alligatoring, blisters, or the paint film is eroded. If your existing paint job is fairly smooth and sound, you do not need to use a primer over the entire surface.
To get the most from you upcoming paint job the first thing to do is to remove all loose paint. Wash your house just like you wash yourself or your car. In other words, use soap and rub the entire surface with a sponge or scrub brush to remove all dirt. Rinse with clear water from a standard hose. Let the house dry for a minimum of two days before you continue.
Apply a rust inhibitive primer to any rusty nails. Countersink these and fill the holes with exterior spackling compound. Prime all bare wood spots and areas on the wood that require a primer. Apply a 100 percent acrylic latex top coat finish paint to all primed areas within 48 hours. This insures that the primer and finish coat will completely bond to one another. The acrylic paint also will not promote the growth of mildew on the paint. Oil based finish paints can support mildew growth.
Be sure to apply a sufficient amount of finish paint to the surface. It is not uncommon for a rookie to overspread the finish paint. Look at the label for the recommended coverage rate. If the label says a gallon of paint should cover 400 square feet, you better have used one half gallon of paint after you have brushed a 10 foot by 20 foot area!
Finally, try to paint when air temperatures are in the 70 F range and the relative humidity is in 50 percent range. Always paint a surface after the sun has passed and it is in the shade. Sunlight that strikes a freshly painted surface can dry a wet paint film too quickly and actually create blisters.