Washing a house before exterior painting

The gritty squeak of a dry rag dragged across a wall means dust, and dust is what paint fails on first. Every teardown that exterior painting riverside cowboy santas has logged shows the same thing: a well chosen topcoat peeling off a wall that was painted dirty. In Riverside, CA, Santa Ana winds lay a fine film over every exterior surface, so washing before painting is a step that cannot be skipped.

What the wind leaves behind

Dry offshore wind lifts dust and ash from the Inland Empire and drops it on walls, trim and window frames. Over a dry summer that film bakes in. Brushing is not enough, because the film is held by body oils from hands, cooking grease near kitchen vents, and spider webs under every eave. Power washing takes all of that off in one pass when it is done correctly.

Pressure limits

More pressure is not better. On stucco a moderate pressure with a wide fan tip cleans without cutting into the surface, and a narrow tip held close will carve grooves into soft sand finish. Wood siding and fascia are worse, since high pressure raises the grain, splits old boards and drives water into joints. Hold the tip well back, move it across the work in even strokes, and work top to bottom.

Efflorescence and stains

White crystals on stucco are efflorescence, mineral salts carried to the surface by moisture. A stiff brush removes the loose crystals, and a mild masonry cleaner takes the rest. The more important job is finding the water: a leaking hose bib, a sprinkler head that sprays the wall, or a failed roof flashing. Painting over efflorescence without fixing the water only buries it for a season. Older stucco and wood sided homes in neighborhoods around Fairmount Park often show these stains below the windows.

Drying time before coating

Dry air is quick but deceptive. The face of a stucco wall may feel dry in an hour while the body stays damp for a day or more. Paint over damp stucco and the coating blisters later. Wood needs even longer. Pressing a hand flat against the wall, or checking with a moisture meter, settles it better than guessing by the clock.

Checking the result before primer

After washing, wipe a dry hand across the wall again. If chalk or dust still transfers, wash again or add a bonding primer. Caulk gaps and do any patching only after the wall is fully dry, then prime, then apply two coats of topcoat. A clean wall also shows cracks and rotted spots that paint would have hidden.