It's not just the inside of a house that gets dirty. Exterior siding can accumulate a lot of dust and grime, even mildew. And because siding is the face we offer the street, even a little dirt shows. Some houses naturally accumulate more dirt than others. If you live along a dusty road or in a new development where lawns are not yet established, you can expect a daily barrage of grit and grime. Textured siding or peeling paint only compounds the problem. When dirt really settles in, the only remedy is a good cleaning with a pressure washer or a scrub brush. We prefer a pressure washer because it's a lot less work.
While cleaning is the focus here, pressure washers also have long been used in paint prep. Handled correctly, a pressure washer can actually strip away peeling paint. It can also scour the surface chalk from aging paint, making a better bonding surface. Wood siding will need a week to dry, and you'll still have to do some scraping. Of course, it's not for every situation, especially when lead-based paints are involved, but it's often worth considering.
A Word on Pressure Washers
Until recently, pressure washers were almost exclusively commercial machines, and they were priced accordingly. In the past 10 years, however, manufacturers have targeted the homeowner with lightweight, general-purpose washers that are priced more like lawnmowers. Electric models, with 1,200 to 1,300 pounds of pressure, start at about $120. Gasoline models, with at least 1,500 psi, start around $220. From there, it's three or four quick steps to 3,000 psi and $700. We chose a basic machine, a 4-hp, 1,600-psi gas model made by Campbell Hausfeld, costing $219 (The Campbell Group, 100 Production Dr., Harrison, OH 45030; 800-330-0712). This is the same unit we used to refinish our deck.
When shopping for a pressure washer, the question for most of us is, how much pressure is enough? For around-the-yard chores, like stripping a deck, degreasing equipment, or washing siding, 1,300 to 1,600 psi is plenty. More pressure is certainly useful in some situations, but it's also more dangerous. All pressure washers can rip through flesh at close range, and more pressure increases the potential hazard. These things may feel like toys, but they're more like chain saws. Better to go slow. Of course, if you're going to need a pressure washer only once a year or so, it makes more sense to rent one. Expect to pay $50 to $75 per day for a typical gas-powered, 2,500-psi unit.
Power washing siding is pretty basic, but there are a few general rules to follow. First, avoid spraying any outdoor electrical components unless they're turned off. Be especially cautious around the electrical service entrance, the lines and conduit feeding the meter. The central air conditioner is another high-voltage shock hazard. Secondly, avoid spraying upward, under siding laps and flashing, and don't get too close to gutters. Thirdly, angle the spray away from doors, windows, and vents, especially soffit vents. And finally, avoid holding the nozzle so close to the siding that the pressure tears the wood or strips the finish from hardboard siding.
In most cases, you'll want to soap your siding before washing it. All general-purpose washers have detergent attachments. Electric models usually have internal reservoirs, while gas models generally have siphon tubes that you insert directly into a container of detergent. As the detergent is pulled through the system, it mixes with water to make an approximately 12 percent solution, suitable for most applications. Because detergent needs extended contact to work effectively, it can be applied only when the machine is in its low-pressure mode. High pressure would blast it off as fast as it was blown on. We chose Campbell Hausfeld's General Purpose Cleaner (No. PW0051), paying $5.99 per gallon. Detergents can pose a problem, however, especially if they contain bleach. Houses are surrounded by grass and landscape plantings, which can be damaged by such chemicals. Root systems can actually survive quite a bit, but foliage is another story. To prevent leaf damage, choose a general-purpose cleaner that does not contain bleach. Then, cover landscape plantings with inexpensive plastic dropcloths. Thoroughly wet any plants you can't cover with plastic. Of course, if your siding is only a little dusty, it may not need a detergent.
If some of your siding has begun to grow mildew, however, a little bleach is required. Mix one part household bleach with 10 parts water and wipe it on the affected area. Then, rinse it away with a sponge and clean water. Using bleach on siding is tricky, so start with as little as possible, for as short a time as possible.
For a larger mildew problem, you might try Jomax, available in paint stores (Zehrung, Chempro Division, 16416 S.W. 72nd Ave., Portland, OR 97224). This mildewcide concentrate requires you to add bleach to the solution, but it deactivates the bleach after it's applied. Therefore, Jomax is said to be harmless to plants and paints. One quart, costing $7.50, makes 5 gal. of solution. Spray it on sparingly with a garden sprayer.
With the mildew problem handled, you're ready to wash the rest of the siding. Begin by connecting a garden hose to the washer's pump. Then turn the water on full bore. Next, set the detergent container next to the washer and slide the open end of the plastic siphon tube over the brass nipple on the underside of the pump. Feed the filtered end of the tube into the detergent container. Finally, slide the spray nozzle forward on the gun, switching from high to low pressure for the soap application. The nozzle can also be rotated to adjust the width of the pattern in the high-pressure mode.
With the water to the pump turned on, start the gas motor and, within a minute of starting, begin to spray an area of the house with detergent, working from the bottom up. The size of the area will depend on weather conditions, especially high winds. You won't want the detergent to dry on the siding before you can wash it off, so keep the size of the area manageable. Allow the detergent to work on the siding for at least 2 to 3 minutes. While the solution works on the grime, remove the siphon tube from the pump. Switch the nozzle to high pressure and rinse the soap from the siding, using a wide spray pattern and holding the nozzle about 18 in. away from the siding. Again, work from the bottom up, without actually spraying upward.
Finally, working from the top down, rinse the siding thoroughly. This time, hold the gun about 10 in. from the siding and spray at a downward angle. If you see spots that won't come clean, try moving the nozzle a little closer to focus the pressure. Watch the siding closely, however. Too much pressure can do real damage. Remember to avoid spraying electrical components directly. Spray carefully around doors and windows, angling the nozzle down and away. Move around the house in this fashion until you've finished the job.
- Cover nearby plantings with a plastic dropcloth. Wet down plants that can't be covered and try to keep them wet.
- Mildew spots usually require a weak bleach solution. Wipe it on lightly, then rinse the area with clean water.
- To add detergent to the flow, hook the siphon tube to the pump with the filter end in the detergent container.
- Apply the detergent at low pressure. Work from the bottom up, and allow the solution to stand several minutes.