General Exterior Surface Prep

When doing exterior painting, it is important to make sure the surface is clean, sound and free of all foreign matter, including dirt, chalk, mildew and loose, flaking or peeling paint. By taking time to adequately prepare the surface, you will be rewarded with a durable paint job that will last for years.

Cleaning the Surface

Every exterior surface should be thoroughly cleansed before painting. In most cases, this will require both washing and rinsing, since even soap residue can prevent paint from adhering properly.

First, be sure to water all plants and shrubs near the house, then cover them with a drop cloth (not plastic, which can magnify sunlight and harm the plants).

One way to clean exterior surfaces is by vigorously hand-washing with a long-handled brush and warm, soapy water (use a commercial cleaner or ordinary household detergent). Start at the top of the wall or other surface and work your way down to the bottom. Thoroughly rinse the entire area immediately after washing it; then move on to the next section.

Although this method is time-consuming, it is effective and low in cost.

Power Washing

To speed surface preparation, consider using power-washing equipment. Fast and effective, power washers use a pressurized spray to rid surfaces of dirt, chalk and mildew – even most loose, peeling or flaking paint. This type of equipment is especially useful when preparing large surfaces for painting and when cleaning extremely dirty surfaces, such as those that contain stubborn contaminants like grease, soot or salt.

Power washers can be purchased from a variety of retailers, or rented by the day or half-day from paint retailers or equipment rental centers.

Operating instructions for power washers are usually provided by the retailer, rental center or the manufacturer. However, there are some important instructions that apply to all power washers:

• First, when power washing lap siding, make sure the water is sprayed in a horizontal or downward direction; power washing at an upward angle can lift or dislodge the siding panels, or force water behind the siding where it can cause damage within the walls.
• Second, never use the equipment near windows, glass doors, lighting fixtures and the like. The force of the spray is strong enough to shatter the glass.
• Third, it is important to keep the nozzle at the specified distance from the surface, usually in the 4″ to 8″ (10cm to 20cm) range. Having the nozzle too close can damage the surface (especially if it is wood), and can force excessive water into wood; on the other hand, having the nozzle too far from the surface will do an ineffective cleaning job.
• Fourth, never point a power washer toward any person or pet, including yourself. The spray is sufficiently strong to cause serious injury.

Eliminating Mildew

One of the most stubborn problems on exterior surfaces is mildew, a type of fungus that has an unsightly black, gray or dark-brown appearance. Mildew can have a general dark cast, or be spotty in appearance. This pesky fungus is especially prevalent in warm, moist environments. However, mildew can be found almost anywhere, especially on shaded parts of the home, such as the eaves, porch ceilings, and on north walls. For good surface preparation, all mildew should be removed before painting.

If you are uncertain whether a surface has mildew or is simply dirty, conduct a simple spot-test: Wearing rubber gloves and eye protection, apply a few drops of household bleach to the area of discoloration, wait five minutes, then rinse off the bleach. If-the discoloration disappears where the bleach was applied, it is probably mildew.

The best method of removing mildew depends on the cleaning method you choose, i.e., hand-washing or power washing.

For hand-washing, simply add one part household bleach to three parts cleaning solution (but do not mix bleach and ammonia). After scrubbing the surface with this solution, let it remain there for 15 minutes, then rinse thoroughly. This will give sufficient time for the bleach to kill the mildew. Serious mildew growth can also be removed with commercial solutions, which tend to be stronger than bleach solutions.

When power washing, use any of the special cleaning agents recommended by the manufacturer of the equipment. Here, too, it is important to follow the cleansing with a thorough rinsing of the surface.

Removing Loose and Peeling Paint

If loose, flaking or peeling paint is present (and it can sometimes be present even after power washing), it is imperative that you scrape and sand the surface before attempting to apply any type of primer or paint. The best way to remove loose paint over large areas is with a heavy-duty scraper. Scrapers with specially shaped heads are handy for getting into tight corners and other hard-to-reach areas. After removing loose paint, use sandpaper to “feather” or level off any rough edges on the remaining paint. (This will help ensure that the newly painted surface will have a smooth finish, and can substantially reduce the chance of premature cracking and loss of adhesion.) Power sanders can be used for this purpose, also.

Caution: If you suspect the presence of old paint containing lead, do not sand the area. Contact your paint retailer for instructions on how to proceed. You may also check with your local town or city government for lead sanding or removal regulations.

Special Situations Requiring Sanding

Even if you don’t have loose or peeling paint, sanding is still a necessity when painting certain types of exterior surfaces. The two most common instances are:

Glossy surfaces. These should be dulled with light sanding so that the new paint will adhere properly. This can be accomplished with a sanding block, liquid sander, or steel wool. An alternative method of preparing glossy surfaces is to forego sanding and use an adhesion primer specifically formulated to adhere to glossy surfaces.

Bare wood. Be sure to sand any unprimed and unpainted wood that has been exposed to the elements for more than a few days. This includes wood used for new construction or for repairs, as well as old wood left exposed by cracking or peeling paint. (Sanded wood should be dusted with a brush, then primed before painting.)

The core content for Painting Tips is provided by the courtesy of Dow Chemical as found on CaliforniaPaints.com.