Cleaning Wood Siding and Shingles the Right Way

The right approach in one paragraph

Clean wood siding with a mild cleaning solution and low pressure. Wet the surface, apply the cleaner, let it dwell so it can loosen mildew and dirt, then rinse gently from the top down. Use a soft brush on stubborn areas. If you plan to stain or paint, let the wood dry fully before anything goes on. That is the whole method; the details below explain why each step matters.

Wood shingles and shakes follow the same rules, only more so, because their thin edges and open grain are even easier to damage.

What high pressure does to wood

Wood is made of soft and hard bands of grain. A strong, narrow stream eats the soft bands first, leaving ridges, gouges and a fuzzy surface of raised fibers. That fuzz looks clean for a day, then grays quickly and soaks up stain unevenly. On shingles, pressure can split thin edges, lift them, or drive water behind them.

You will sometimes see wand marks on wood: faint stripes or arcs where the stream lingered. Those are permanent until the wood is sanded. Lower pressure with a wider fan and more reliance on the cleaner avoids them.

Mildew, gray weathering and tannin stains

Black or green spotting in shaded areas is usually mildew or algae. It responds to a soft wash solution and dwell time. Gray, silvery wood is weathered surface fibers broken down by sun. A cleaner removes the loose gray layer, but heavily weathered wood may need a dedicated wood cleaner and brightener rather than just a wash.

Redwood and cedar, both common in older LA homes, can bleed brown tannin stains when wet. That is natural, not damage. A wood brightener usually evens it out. Be careful with strong bleach-based mixes on these woods, because they can blotch the color and are harsh on bare fibers.

Older shingle homes may also have moss or lichen on north-facing walls. Let the solution soften it, then lift it with a brush rather than trying to blast it off the shingle.

Preparing wood for stain or paint

Washing before refinishing is one of the best things you can do for wood. New coatings need clean, sound fibers to bite into. Mildew left under paint keeps growing, and dirt and chalk under stain cause peeling.

After washing, wood needs time to dry. How long depends on sun, shade and temperature. In hot, dry Valley weather a sunny wall may be ready sooner, while a shaded wall near the coast under the marine layer can stay damp much longer. Follow the coating manufacturer's moisture guidance, and if your painter has a moisture meter, let them check. During the rainy season, roughly November to March, plan around the forecast.

If the wood still feels fuzzy after drying, a light sanding before staining gives a smoother, more even finish.

When cleaning is not enough

Cleaning cannot fix rot, split boards, loose shingles or failed paint. Press a screwdriver into suspicious areas, especially near the ground, under windows and around downspouts. Soft wood needs repair, not washing, and pressure on rotted wood can tear it apart. Peeling paint will often come off during a wash; that is not damage from the wash, it was already failing, but it does mean the surface needs scraping and priming before repainting.

Note any of these spots before the cleaning so you can plan the repair work in the right order.

What to expect from a professional wash

Expect the crew to wet plants, close windows, work in sections, and keep pressure low enough that the wood is cleaned by the solution rather than the stream. Shaded walls with mildew usually show the biggest change. Weathered gray boards will look cleaner and more even, though not like new lumber.

When Say Wash It washes wood-sided homes, we walk the house with you afterward and point out any soft or damaged boards we noticed. House washing is $0.35 per square foot of exterior wall as of October 2026, and wood fences, if you want those done too, are $2.15 per linear foot. Booking two services in one visit earns a 5% bundle discount.