Pressure washing, also called power washing, is a good way to clean a house exterior or prep it for a new paint job. Spraying water and, in some cases detergent, at high velocity, a pressure washer cleans dirt, grime, and chalk-like residue, as well as deteriorating paint, from the surfaces of siding and trim. This is an excellent first step to ensure that a new coat of paint will last.

A pressure washer can be used on most siding materials, including vinyl, metal, and some types of masonry. It is not meant to be used on wood siding or brick—holding a strong spray in one place long enough to remove paint can erode soft wood grain or dislodge mortar from between bricks. It should also not be used on hardboard siding, because moisture is hardboard’s worst enemy, and it also shouldn’t be used on stucco because it can damage the surface.

In addition, do not pressure wash your house if you suspect that it may have been painted with lead paint prior to 1978 (contact your public health department or the EPA at 800-424-LEAD). If your home is two stories or very large, it’s safer to let a do the job.

You can rent a pressure washer from most rental equipment dealers for about $50 to $75 a day. They come in various sizes for different types of jobs, from about 1200 to 3000 psi (pounds per square inch, the power of the spray). A 1200 to 1500 psi model is safer to use with a vulnerable material such as aluminum; you can use a stronger 2500–3000 psi model for a material that doesn’t have a painted surface, such as vinyl. The stronger types work faster. Choose one that will allow mixing detergent into the spray. Plan to mix about 1 pound of TSP (or a non-phosphate substitute) into every 4 gallons of water for the washing (rinse with water only). And before starting, scrub any mildew from the surface.

When operating the power washer, use both hands and never use it while standing on a ladder. For high areas, rent a 6- to 12-foot adjustable extension shaft, but be aware that this can be a bit tricky to handle.

Start with the nozzle about 3 feet from the wall and work your way closer until you feel the spray is strong enough but not too strong. Never get closer than 12 inches from the siding or you may damage it; do not point it at windows and avoid aiming it upward, where it might drive water under the siding. Remember, this is extremely high pressure, so never point the nozzle at anyone and be sure to wear safety glasses. Also keep the wand, the water, and yourself away from any electrical wires or devices.

1) Protect any plants, light fixtures, or other breakable objects around the house with plastic bags, duct tape, and drop cloths. Move obstacles and outdoor furniture away from the house.

2) Connect the pressure washer to a garden hose. If the machine has a detergent dispenser, fill it with the cleaning solution.

3) Working from the top down, hold the wand at about a 45-degree angle, and spray soffits, overhangs, gutters, and downspouts. Then move it across the siding from side to side at a steady pace. Hold the nozzle a couple of feet from the wall and adjust its distance back and forth for the best cleaning action. As well as you can, direct the water slightly downward so it isn’t blasted up under horizontal lap joints of the siding. When working near windows, direct the nozzle away from the window, holding the wand at an angle so you don’t drive water into the window or frame.

4) Rinse off the siding with clear water, using a garden hose, working from the top down. If you plan to paint, allow the siding to dry for at least two days.

Get Your Exterior Surfaces Pressure-Washed by Pre-Screened Local Contractors