How to pressure wash your house (© Steve Cole/Getty Images)

© Steve Cole/Getty Images

Q: Either I'm doing something wrong or my electric pressure washer doesn't cut it. I pressure wash my house every summer to remove dirt and mildew, but the results are less than sparkling. Can you tell me how to do this so I'm not wasting my time?

A: Until they gain some experience with a pressure washer, homeowners tend to look upon one of these machines as if it were a magic wand. Wave it over your house, car, truck, boat or tractor and, presto, it's clean. As usual, the truth is a bit more complicated and subtle than that.

Pressure washers do live up to their billing in that they are incredibly productive and water-conserving. But, as with any other piece of outdoor power equipment, you have to select the right machine, then use it correctly. (Bing: Pressure washing techniques)

First, unless you have a very small house or a house that's not particularly dirty, it's likely that an electric machine is not powerful enough to do the job. These machines are better suited to cleaning cars, small boats and patio furniture. Pressure-washer capacity is measured in cleaning units, the product of water pressure (in psi, or pounds per square inch) multiplied by flow rate (in gpm, or gallons per minute). An electric pressure washer may operate at 2,400 cleaning units; a homeowner-grade gas-engine model can operate at up to 6,210 cleaning units, and professional machines can hit 16,000 cleaning units (4,000 psi and 4 gpm). Cleaning units translate directly into effectiveness.

So, let's say you spring for a gas-engine machine. Will that solve your problems? It's likely to help, but I wouldn't count on the machine alone to do a really thorough job. I find that I get the best results when I use a pressure washer in conjunction with hand tools.

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If the mildew is not severe, pressure washing alone will do the trick. But if it's bad, I pre-treat the mildew-stained areas using nothing more than a pump garden sprayer loaded with a solution of liquid bleach, Jomax mildewcide and water.

I spray this on, scrub, rinse and then pressure-wash with a multipurpose siding cleaner. It leaves an immaculate, streak-free surface. And when I use the pressure washer, I've had better results washing from the bottom up and rinsing from the top down. Professional contractors, who move a lot faster than I do and often work in squads, wash and rinse from the top down. Since I'm not a professional, my goal is to take my time, work safely and get the house clean enough so that it won't need to be done again for at least another year, maybe longer.

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Clean is good, injury bad
Take steps to avoid injury and damage while pressure washing.

Water and electricity don't mix. You're going to get wet when pressure washing, and that puts you at risk of receiving an electrical shock from wires and exterior outlets. Look overhead to check for power lines before placing or extending ladders. Avoid blasting the house's electrical-service entrance cable, the electrical meter, exterior outlets and exterior lights.

Stand firm. Position the ladder on a firm footing at the proper angle (about 75 to 78 degrees). To assess the angle, place the toe of your boot against the ladder's base. With your arms straight out, you should be able to rest your hands on the rung in front of you (usually the fifth rung). Obviously, the most dangerous part of this work is operating a pressure washer with two hands while standing on a ladder. If you're at all uncomfortable with ladder work, hire a professional. Otherwise, take your time, lean against the ladder, and stop if you feel uneasy.

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Do no harm. Try a pressure nozzle with a wider fan pattern before resorting to one with a narrower pattern. Yellow nozzles spray at a fan pattern of 15 degrees, green at 25 degrees and white at 40 degrees. Reserve the red nozzle (zero degrees) for unusual applications like stripping off hardened mud. Keep the nozzle moving, and hold it the recommended distance from the surface. Avoid blasting water upward at a steep angle under siding. Also, don't blast directly into corners, under the edge of windows and doors or into dryer or attic vents.

What you'll need
Aside from a pressure washer, you need other gear:

  • Five-gallon buckets, to mix cleaning solutions.
  • House wash, a cleaner formulated specifically for pressure washers.
  • Mildewcide to pre-treat areas with severe mildew.
  • Bleach to mix with mildewcide and water to treat severe mildew.
  • Pump garden sprayer to apply bleach and mildewcide solution to the house.
  • Fiberglass extension pole and soft siding brush, to scrub anything that can't be sprayed.
  • Measuring cup to mix cleaners (don’t guess at amounts).
  • Stiff deck brush for tough scrubbing jobs.