That greasy, slick film on your walkway every winter is usually algae — not just wet concrete. Here’s why it forms and how to get rid of it.
Walkways, steps and patios get slippery in winter mainly because a thin film of algae and organic buildup grows on concrete and pavers that stay damp and shaded for months. The film turns slick when wet. Cleaning it off with controlled pressure washing, then keeping the surface clear of leaves and standing water, is what restores grip.
In the Fraser Valley’s wet season, a lot of hard surfaces around a home never fully dry out — the north side of the house, paths under trees, steps below a roofline, patios next to lawns. That’s the environment algae and moss need.
What’s actually making it slippery
- Algae film — often a dark green or black stain that feels slick underfoot when wet
- Moss — especially in paver joints, expansion cracks and along edges
- Decomposing leaves and needles — they hold moisture against the surface and feed more growth
- Standing water — from low spots, downspouts, or gutters overflowing onto the path
Where it shows up first
Shaded entry steps, the walkway along the side of the house, patios under trees, and the first few feet of a driveway nearest the garage. For businesses and multi-unit properties, it’s entrances, ramps and common-area walkways — where the most people walk.
How to fix it
Clean the film off, not just the dirt
Rinsing with a garden hose won’t lift an established algae film. Concrete, pavers and brick are durable enough for controlled pressure washing, which removes the film and embedded buildup — with even technique so the surface doesn’t end up striped. Paver joints need care so jointing sand isn’t blasted out.
Then keep the conditions from coming back
- Keep leaves and needles swept off shaded paths through fall
- Make sure downspouts discharge away from walkways
- Trim back plants that keep a path permanently shaded and damp, where practical
- Book a cleaning before the worst of the wet season rather than after the film is thick
For businesses and managed properties
Slippery entrances are a customer-experience and safety problem, not just an appearance one. A regular cleaning schedule for walkways and entries is part of our commercial exterior cleaning, scheduled around operating hours where practical.
For more on hard-surface cleaning, see why driveway cleaning is worth it and why Chilliwack driveways darken so quickly.