You’re looking at a streak of green on the siding that has bugged you since last fall, and the urge is to get it off fast. But speed and water pressure are a risky pair. Some mistakes start before the water flows, some happen while the machine runs, and some show up once everything looks dry. For what a fair job costs, see our house washing cost guide.

Before the wash

Skipping the siding guidance. Siding makers don’t agree on one pressure, so there is no single safe setting.

Siding Guidance Source
Vinyl 40-degree tip, 1,500 to 2,400 PSI, don’t aim upward Ply Gem care guide
Fiber cement Wide fan tip, 6 feet or more from the wall, under 1500 psi James Hardie care guide

A fiber-cement siding maker also notes that damage from improper cleaning or maintenance may not be covered by its warranty. Read the guide for your own siding before you pick a setting.

Forgetting what could be in the paint. The EPA says a home built before 1978 is more likely to have lead-based paint, and its simplest advice is to assume your home contains it and take the appropriate precautions. The EPA’s lead pages explain those precautions, so start there.

Taking the lowest bid without a second look. The FTC says not to automatically choose the lowest bidder, and to ask for an explanation if estimates differ widely. It also advises asking the contractor for proof of insurance. Our guide to questions to ask a house washing company walks through that call.

Ignoring the plants. A fiber-cement siding maker’s cleaning bulletin says to shield any landscaping or vegetation. A cleaner maker’s label goes further and says to rinse nearby plants and grass with water before and after pressure washing.

On the day

Skipping the test. A vinyl siding maker says to test any cleaner on an inconspicuous area before applying it to major areas. That is a good habit to follow before you commit to a whole wall, and it applies to wood too, as in deck prep before you stain.

Working from a ladder. A pressure washer manual says plainly: do not use the pressure washer while standing on a ladder. It warns that the spray’s reactive force will make the wand kick back, which could cause the operator to slip or fall. Treat that as a stop sign.

Spraying upward behind the siding. A vinyl siding maker says not to aim the washer upward, because water may collect behind the siding and cause leaks, streaks and decay. A cleaner maker’s label says to point the nozzle at a downward angle and keep at least 18 inches from the surface to avoid driving water behind the siding.

Spraying near electrical parts. The same pressure washer manual warns that spray directed at receptacles or switches could cause a fatal electrical shock, and says to direct the spray away from them. A national electrical safety nonprofit calls a GFCI, which cuts power when a plugged-in product leaks electricity, “a lifesaver, not a luxury” outdoors. For your own setup, follow the manual and ask a qualified electrician if you’re unsure.

Letting cleaner dry on the wall. A cleaner maker’s label says not to let its product dry onto the surface, or it gets harder to rinse. A fiber-cement siding maker suggests cleaning a small section at a time and starting at the top, working down, to prevent dripping or streaking onto the cleaned area.

After the job

Skipping the walk-around. Look over each cleaned area once it’s dry. If you hired a pro, look together before they leave. If a problem turns up later, the FTC says to try to resolve it with the contractor first, follow calls with a letter, and keep notes and copies of letters and documents. If you are unsure the wash caused a mark, telling wash damage from damage that was already there is a useful read.

Assuming you’re done. Check your siding maker’s care guide for how often to clean and what to use between washes. Orange dots on concrete are a different problem; see rust spots on a driveway after a lawn treatment. For regional looks at upkeep, see Louisiana’s heat and humidity and house exteriors and Montana’s freeze-thaw and road grit. For how we check the facts in our guides, see our methodology, and for more on the numbers, our pressure washing cost guide.

Sources