Power Washing Stucco and Wood Done Right

The power wash is the first thing that happens on an exterior repaint, and it is the step most often done badly. A machine that can strip paint off a fence can also strip the texture off stucco, splinter soft wood, and push water behind windows and into the wall cavity. Done right, it is a careful cleaning of every surface that is about to be painted. Done wrong, it creates repairs that were not there in the morning.

Why wash at all?

Paint bonds to whatever it touches. On a San Diego exterior that is rarely the wall itself: it is chalk from the old paint on sunny elevations, dust from open ground, cobwebs under the eaves, mildew on shaded walls and, near the coast, salt. All of it has to come off. The wash also makes the next step, the repair check, far more reliable, because hairline cracks and soft wood show plainly on a clean surface.

What is the right pressure for stucco and for wood?

There is no single number. The useful rule is the least pressure that cleans the surface, with a wide fan tip held at a working distance. Stucco takes moderate pressure; wood takes less. If the spray is marking, furring or eroding the surface, the pressure is too high or the nozzle too close.

Washing stucco

Stucco is hard but porous, and its finish texture is a thin layer that can be worn away.

• Wide fan tips, not the narrow or rotating tips used for concrete. A pencil-thin jet cuts lines in sand finishes and blasts the tops off dash.
• Spray angled down and kept moving. Water aimed upward at a wall goes behind trim, under window frames and into vents.
• Distance matters as much as pressure. Moving the nozzle back softens the impact without losing coverage.
• Cleaner where needed. Chalk and grime often come off better with a suitable exterior cleaner and a lower-pressure rinse than with brute force.
• Watch the cracks. A strong jet pointed straight into a hairline crack forces water into the wall behind it.

Inland, in Santee and around the open ground on the edges of the valley, dust settles deep into stucco texture, and it is the texture, not just the face, that has to come clean. A wall that looks clean wet can still have dust in its grain once it dries, so the dry wall is checked again.

Washing wood

Wood is softer than it looks, especially old, weathered wood.

• Lower pressure than stucco, with a wide tip, working along the grain.
• No gouging. Weathered fibers tear under a strong jet, leaving a furry surface and lines that show through paint.
• Raised grain after washing is common on bare or weathered wood and usually needs a light sanding once dry, before primer.
• Loose paint that comes off in the wash is a sign of what the scraping step will find; the wash is not the scraper.
• More drying time. Wood holds water longer than stucco, and its end grain and bottom edges longest of all.

Older homes in National City often have wood trim and siding with many layers of old paint. Before washing those surfaces, it matters whether the house was built before 1978, because high-pressure water on failing paint that contains lead spreads chips across the yard. The EPA’s lead rules apply to anyone paid to disturb paint in a pre-1978 home, and the method changes. Ebenezer is EPA lead-safe (RRP) certified, so on those surfaces he plans the wash and the clean-up the lead-safe way.

What gets protected before the wash

Water is going everywhere, so the house is prepared for it:

1. Windows and doors closed, and any with failed seals noted, since they will leak under spray.
2. Electrical fixtures, outlets and lights on the exterior covered or carefully avoided.
3. Vents, including dryer and attic vents, not sprayed into directly.
4. Plants near the walls wetted first and rinsed after if a cleaner is used.
5. Cars, patio furniture and anything near the house moved or covered.
6. Runoff kept out of storm drains as far as possible, particularly when it carries old paint chips or cleaners.

Hillsides and heights

On sloped lots, common in Spring Valley, water from the upper walls runs down onto the lower ones and onto the ground below. The wash works from the top of each wall down, and the lower side of the lot, which already tends to stay damp and shaded, gets extra drying time. Second-story walls and eaves are washed from a ladder or with an extension wand rather than by aiming a strong jet upward from the ground.

How long does it have to dry?

Until the surface is truly dry, and that varies far more than people expect. A south-facing stucco wall on a warm inland afternoon may be dry by the end of the day. A shaded north wall, a wood fascia, or any wall on a foggy morning near the coast can take until the next day or longer. Paint and primer labels are consistent on this: do not coat a damp surface. Coating over trapped moisture leads to blistering and peeling, and it undoes the point of washing.

This is why the wash and the first coat are rarely on the same day, and why a painter who washes in the morning and paints the same afternoon deserves a question.

What the wash tells you

A careful wash is also a diagnosis. Paint that lifts in the spray had already lost its bond. Wood that softens or splinters has rot. Water that disappears into a crack shows where the wall is open. Ebenezer uses what the wash reveals in the repair check that follows, and tells you what he found before anything is masked or painted. It is the first of the four steps on the process page, and nothing goes on the wall until it is done and dry.

If you would like to know what a proper wash would turn up on your house, and how the rest of the job would follow from it, ask for a free estimate. Ebenezer will walk each wall with you and explain what he sees. Read more about exterior painting.