Exposed aggregate hides dirt at first, then seems to go dark all at once. Here’s what’s building up between the stones and how it comes out.
Exposed aggregate driveways turn dark mainly because algae, mildew, dirt and organic debris settle into the textured surface between the stones and hold moisture there. In the Fraser Valley’s wet months that film grows quickly. Controlled pressure washing, done evenly and with care around loose stones, lifts it out and brings the stone colour back.
Exposed aggregate — concrete with the top layer washed away to reveal the stones — is one of the most common driveway and patio finishes around Chilliwack. It’s durable and grippy, but its texture holds far more grime than a smooth broom finish.
What’s making it dark
- Algae and mildew growing in the crevices between stones, especially in shade
- Dirt and fine debris washed or tracked into the texture
- Organic staining from leaves, needles and seed pods left to sit
- Tire marks and traffic grime on the parking area
- An old sealer — a worn or discoloured sealer can darken or yellow the surface; that’s a sealing question rather than a cleaning one
The same film that darkens the driveway also makes it slick — see why walkways and patios get slippery in winter.
How exposed aggregate is cleaned
Exposed aggregate is a durable hard surface, so controlled pressure washing is the right method. Technique matters more than raw power: consistent passes avoid a striped finish, and care is taken on edges and any areas where stones are already loose so they aren’t dislodged. Heavier organic buildup may be pre-treated before cleaning.
What to expect afterwards
- The stone colours come back once the film is removed
- Oil and rust stains that have soaked into the concrete may lighten but not always disappear completely
- Shaded sections will regrow algae faster than sunny ones — a yearly cleaning keeps most driveways ahead of it
Should you reseal afterwards?
Some owners choose to reseal exposed aggregate once it’s clean. That’s a separate job — if you plan to reseal, have the cleaning done first and ask your sealing contractor how long the surface should dry beforehand.
Book it with the rest of the exterior
Driveway and walkway cleaning is included in our Gold and Platinum exterior cleaning packages, or it can be booked on its own. For more, see why driveway cleaning is worth it and why Chilliwack driveways darken so quickly.