Washing is the first step of every exterior repaint because paint makers require clean, dry surfaces free of dirt, chalk and mildew. The siding then has to dry fully before scraping and priming, and on homes built before 1978 washing must not spread old paint chips across the yard.
Paint only bonds to what it touches. Benjamin Moore's Aura exterior data sheet says surfaces must be clean, dry and free of oil, grease, wax, rust, mildew, chalk and loose or scaling paint, and that sheltered areas such as eaves, porch ceilings, overhangs and protected walls should be washed because they never get rinsed by rain. Chalk, the powder that forms as old paint weathers, is a common reason new paint fails to stick.
Siding of every type, trim, soffits, porch ceilings, decks and masonry. Benjamin Moore's Woodluxe All-In-One Wood Cleaner is listed for wood decking, siding, fencing, shakes and furniture and also for vinyl, stucco, concrete, pavers and brick, to remove dirt and stains from mold, mildew, algae and water. Each surface gets the pressure and cleaner it can take; soft wood and old mortar are easy to damage with too much pressure.
Yes, for cleaners. Benjamin Moore says not to apply its Woodluxe cleaner when air and surface temperatures are below 50°F. In the Lehigh Valley, NOAA's 1991-2020 normals show average highs of 63.4°F in April and 65.5°F in October, so shoulder-season washing is planned for the warmest part of the day.
Long enough to be dry. The Aura data sheet requires dry surfaces, and James Hardie tells installers not to paint wet fiber cement siding. Wood holds water longer than vinyl or aluminum, and shaded walls dry slower than sunny ones, so painting usually starts after the siding has had time in dry weather following the wash.
On homes built before 1978, loose paint knocked off during washing may contain lead. The EPA's renovation rule sets exterior work practices for paid jobs that disturb paint, including covering the ground with impermeable sheeting 10 feet beyond the work area and collecting debris. Ask how a contractor contains and collects chips on an older house before any washing starts.
Chalk is the fine powder that forms on the surface of exterior paint as sunlight breaks down the binder. Rub a dark cloth or your hand across a sunny wall: if it comes away coated in color, the paint is chalking. Benjamin Moore's Aura exterior data sheet lists chalk among the things that must be removed before painting, because new paint applied over chalk bonds to powder instead of the old coating.
Yes. Masonry is porous and holds water longer, and old mortar and stucco can erode under high pressure. Benjamin Moore lists its Woodluxe cleaner for stucco, concrete, pavers and brick, and its Aura exterior sheet requires new masonry to cure for 30 days before painting, with surfaces of pH 10 or higher sealed or primed first. Portola's lime wash data sheet also calls for removing salts and efflorescence from masonry before coating.
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It can if pressure is too high or the nozzle is too close. Soft wood fibers can be raised or gouged, water can be driven behind vinyl and aluminum laps and into window frames, and old mortar can be eroded. The right approach is the lowest pressure that cleans, a cleaner that loosens mildew and dirt, and spraying downward with the laps rather than up under them.
Yes. Vinyl collects dirt, pollen and mildew that keep paint from bonding, and Benjamin Moore's Aura exterior data sheet requires clean, dry surfaces before painting any siding. Its Woodluxe cleaner is listed for vinyl as well as wood. After washing, vinyl dries faster than wood, but it still needs to be dry before primer or paint goes on.
Washing with water alone often leaves mildew roots behind; a cleaner made for mildew does more. Benjamin Moore lists its Woodluxe All-In-One Wood Cleaner for removing stains from mold, mildew, algae and water on wood, vinyl, stucco and masonry, applied above 50°F. Paint makers require surfaces free of mildew before painting because coatings over live mildew can discolor.
Not necessarily. Washing is most useful before painting and whenever dirt or mildew builds up on north-facing or shaded walls. Gentle annual cleaning of those areas can help paint look better longer. Aggressive high-pressure washing every year can wear wood and drive water behind siding, so the gentlest method that works is better.
Sources: Benjamin Moore Aura Waterborne Exterior Soft Gloss (N632) technical data sheet; Benjamin Moore Woodluxe All-In-One Wood Cleaner (018) technical data sheet; James Hardie HardiePanel installation requirements (HS1237); NOAA NCEI 1991-2020 Climate Normals, Lehigh Valley International Airport (USW00014737); EPA Renovation, Repair and Painting rule, 40 CFR Part 745 Subpart E; Portola Paints Lime Wash technical data sheet (rev. 02.28.25). Figures checked October 2026.
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