Before a deck can be stained, sealed, or made to look new again, the surface has to be truly clean and smooth. In Seattle that means removing moss, algae, mildew, grey oxidized wood fibers, and whatever is left of the old finish — without tearing the wood apart with a pressure washer. Alexandria Builders offers professional deck washing and sanding across Seattle and the Eastside as a stand-alone service or as the first step of a full restoration.
Deck Washing Done Right
A pressure washer on full blast is the fastest way to ruin a cedar deck: it raises the grain, carves lines into the soft summerwood, and drives water deep into the boards. Our process is different:
- Clear and inspect. Furniture off, gaps cleared, and a check for loose boards, raised nails, and rot before any water goes on.
- Apply a deck cleaner. An oxygen-based or sodium-percarbonate cleaner lifts dirt, mildew, and grey fibers. For old solid stain we use a chemical stripper rather than brute force.
- Low-pressure rinse. A wide fan tip at 500–1,200 psi, kept moving with the grain — enough to rinse, not enough to etch.
- Brighten. An oxalic-acid brightener neutralizes the cleaner and restores the wood’s natural color, so the stain goes on evenly.
- Dry. Wood needs to drop below roughly 15% moisture before finishing. In a Seattle summer that is 2–3 dry days; we schedule around the forecast.
When Sanding Is Needed
Washing cleans; sanding renews. We sand when the surface is splintered or fuzzy after washing, when there is a failing film finish that stripping will not fully remove, when boards have cupped and need to be flattened, or when you want a fine, smooth, bare-foot-friendly surface before a penetrating oil. We use orbital and drum sanders at 60–80 grit, then set every fastener below the surface first so nothing tears the paper — or your feet.
Hardwood decks (ipe, cumaru, tigerwood) almost always benefit from a light sanding before oiling; the dense grain seals itself and a fresh surface is what lets the oil penetrate.
Composite Deck Cleaning
Composite does not need sanding — and should never be sanded — but it does grow mold in the shade here. We clean Trex, TimberTech, and Fiberon decks with manufacturer-approved cleaners and a soft-wash rinse that keeps your warranty intact.
What It Costs and How Long It Takes
Washing and brightening a typical 300–400 sq ft deck is a one-day job. Adding sanding or stripping makes it two to three days. Pricing depends on square footage, the condition of the old finish, and whether railings and stairs are included; we quote a fixed price after seeing the deck. Most homeowners pair washing with staining and sealing so the clean surface is protected before the rain comes back.
Call (425) 866-0594 or request a free estimate below.