Just because everyone knows that paint adheres longest to clean surfaces doesn’t mean that everyone should use a pressure or power washer to prep a surface for primer and paint. Yes, exterior surfaces are covered with dirt, environmental pollution, mildew, moss and chalking, peeling, and flaking paint. However, pressure washers are dangerous tools that should not be operated by a weekend do-it-yourselfer.

A pressure washer utilizes an electric or gas engine with a pump to increase the water pressure from a faucet so that a water jet leaves the wand, becoming a high-power cleaning device.

The pressure (2,200 to 3,500 psi) needed to remove stubborn peeling paint can etch wood, brick, and concrete, and blow mortar from joints and stucco from walls. The water blast can also weaken the good paint around the peeling paint. A narrow high-pressure stream of water can cut through layers of wood fiber leaving divots and splintered wood.

When wood fibers are crushed, paint has a less sturdy surface to adhere to. And pointing the pressure washer upward on walls with shingles or lap siding will force water behind the siding, soaking the insulation and wiring.

Additionally, painting over wood that appears dry on the outside but has water forced into its interior will cause your paint job to peel and blister as the interior moisture forces its way out. Dry rot can begin in homes with no vapor barrier once the water gets between the siding and interior walls.

If any layer of the exterior paint contains lead, power washing should not be attempted. The force of the water will blast lead-contaminated debris all over the ground.

Part Art, Part Science
One problem with pressure washers is that their force is determined by many factors that take practice to learn to use together.

• Engine speed determines how much water is delivered per minute.
• Basic tips are identified by their spray width from 40, 25, 15, and 0 degree. The 40 tip emits a soft, flat fan ideal for rinsing surfaces. A 0 tip sends out a piercing narrow stream.
• The distance the wand is held from the surface will influence the water’s force. Water’s velocity and its impact drops quickly as it leaves the nozzle.

Pressure, water flow, and distance must be kept in balance so no part of the surface gets cleaner than another, and no surface is eroded.

Safety 101
If you insist on pressure washing, read the safety directions that come with the unit. If you rent a unit insist on receiving the directions.

Buy or rent an extension for the pressure wand. Do not use a pressure washer on a ladder. The hose is stiff and the wand has kick that has caused many people to lose their balance and fall off ladders.

Do not point a pressure washer at anyone or anything. Water under pressure going through a pinhole nozzle can slice off fingers. Even low powered pressure washers can force water laced with cleaning chemicals through skin and into the bloodstream.

Power washers that heat water to 200 degrees are extremely dangerous. Water at 140 degrees causes burns serious enough to require hospitalization.

The hot engine service of any operating power washer can cause burns. Shut off the engine and wait five minutes before refueling a gas engine to allow it to cool.

Electric pressure washers are quieter than gas engines but they top out at 1,000 psi. They must be plugged into a ground fault circuit interrupter.  Spraying electrical wires is a deadly mistake — electricity can follow a water stream back to the sprayer. Avoid electric outlets since water can cause short circuits.

Never use a gas engine without proper ventilation. Carbon monoxide poisoning is deadly. Don’t spray at windows or light fixtures, as you will be showered with glass. Make sure the tip is fully attached to the wand before the power washer is started. Always wear goggles and rubber gloves to protect your face and eyes and rubber clothing to keep you dry. Wear earplugs for protection from the noise.

Buying Tips
Higher pressures and bigger flows demand bigger engines. Top-of-the-line machines cost thousands of dollars but last many times longer with their belt-driven general pump, dissipating heat and reducing vibration, which helps to extend the life of the power washer.

Small power washers selling for under $500 have a short life expectancy, often only 150 hours, and are thought of by many contractors as disposables. A painting contractor using a power washer as a scraper will use a machine that delivers at least 3.5 gallons of water at a pressure of 3,000 psi.

Avoid washers that circulate chemicals through the pump because bleach and detergent damage pistons and valves. Pressure washers with “downstream injectors” put chemicals into the water after it has been through the pump.

Practice
Wear rain gear and get the feel of the hose and wand as they stiffen with pressure. Practice on the sidewalk. Move the wand in sweeping motion while turning it on.

Start at the bottom of a wall with the wand pointing downward move the wand in the direction of the siding or wood grain. Use overlapping strokes until the top of the wall is reached. Rinse the wall with clear water with the sweeping motion starting at the top and working across and down.

Learn to feather the ends of each stroke by pulling the wand back as the end of the stroke approaches. Have the wand moving when the wand is switched on. Never hold the wand in one spot or stop the wand abruptly.

Prep Without Power Washing

Power washing is no substitute for hand scraping, wire brushing, and hand sanding. Handwork takes longer but the control is worth it.

Wear safety goggles. Remove grime and cobwebs using a mixture containing two gallons of water and one cup of detergent and a scrub brush. Rinse with a garden hose. A car wash brush attached to a garden hose also helps with the scrubbing.

If the surface still has brown or black discoloration, it probably is mold and mildew. Wet exterior plantings, then cover with plastic to protect them while using a scrub brush and three parts water and one part bleach on the discoloration and one foot around it. Keep the area saturated with the bleach solution for 20 minutes, then rinse completely. Remove plastic on shrubs immediately or they will sun scald.

Let it dry, depending on the temperature, 24 to 48 hours, then work to remove the lose paint.

With a 6 inch to 8 inch wide putty knife or a 5-in-1 tool, get under the weakest edge of the lose paint and lift and scrape it away. Work with the wood grain. Use the hook corner edge of the 5-in-1 tool to dig out chipped and cracked chalk.

• Use sandpaper to feather the edges of any stubborn paint chips that remain.
• Remove dust with a tack cloth.
• Prime and paint.

Paulette Rossi is an outreach specialist for MetroPaint, the first recycled paint program to earn the Green Seal certification.  For more information on MetroPaint, visit www.oregonmetro.gov/paint or call 503-234-3000.