We Pressure Washed 3 Driveways in One Week in Vancouver — Here's What We Found Under the Moss

Moss on your driveway looks like a cosmetic problem. It isn't.

Moss retains moisture against your concrete surface for weeks at a time — long after the rain has stopped. That sustained moisture accelerates spalling: the surface layer of the concrete absorbs water, freezes during cold nights, expands, and breaks away. The same biology that damages roofs in the Pacific Northwest — where moss can halve a typical 25–30 year shingle lifespan according to roofing researchers [1] — applies to any porous surface it colonizes, including concrete. [2]

Over two or three winters, a moss-covered driveway can go from surface staining to active deterioration that no amount of pressure washing will fix. Here's what we found on three Clark County driveways this spring.

Driveway 1: Vancouver — Surface Checking and Oil Staining

This driveway had about two years of moss growth concentrated along the shaded north side. Under the moss, we found hairline surface cracks running with the aggregate pattern — a sign of multiple freeze-thaw cycles with retained moisture. We also found oil staining masked by the moss. The cracks were surface-only, not structural. After cleaning, we applied a penetrating concrete sealer to slow future moisture absorption.

Driveway 2: Battle Ground — Joint Erosion

The second driveway was poured in the mid-1990s, and the expansion joints had lost most of their filler material. Moss had colonized the joints heavily, accelerating erosion of the joint edges. After cleaning, we re-filled the expansion joints with a flexible polyurethane sealant — a simple repair that most homeowners overlook, but open expansion joints are one of the primary entry points for water that causes slab heaving over time.

Driveway 3: Camas — Clean Bill of Health

The third driveway looked the worst before we started — heavy moss coverage across the full surface. But under the moss, the concrete was in excellent condition. The homeowner had sealed it about three years prior, and the sealer had done its job. A thorough pressure wash, a moss inhibitor treatment, and a fresh coat of sealer — and this driveway is good for another five years.

What This Means for Your Driveway

The pattern we see consistently across Clark County: homeowners wait until the moss is visually obvious before calling. By that point, the moss has usually been there for two or more years — which means the moisture damage has already started. The difference between a $250 cleaning and a $2,000+ resurfacing job is often just one or two seasons of waiting.

"The difference between a $250 cleaning and a $2,000 resurfacing job is often just one or two seasons of waiting." — Marcin Micek, Handy Pioneers