A slippery deck is a safety problem before it's an appearance problem, and it nearly always traces back to water sitting on the surface for too long. Solve the water and you largely solve the slip.
Diagnostic timeline
Work through these steps in order before booking a repair.
- 1
Check whether the whole deck or only the shaded section is affected.
- 2
Pour a bucket of water and watch where it runs — or where it stops.
- 3
Inspect the grooves for compacted debris.
- 4
Probe a few boards while you're down there; slipperiness and rot often arrive together.
Likely causes
Algae and biofilm
A thin, slick organic film builds in shade and is invisible until it's wet.
No fall or blocked grooves
Water sits in the board grooves rather than running off; grooves clogged with debris hold it longer.
Leaf litter under trees
Decomposing leaves feed the biofilm and keep the surface damp permanently.
Smooth board profile
Some smooth timber and early composite boards offer very little texture when wet.
Fix options, full-width
Deep clean and biocidal wash
Boards are soundDebris cleared from the grooves, biofilm removed, and the deck allowed to dry properly.
Anti-slip strips or inserts
Steps and traffic routes are the dangerGrit strips let into the boards on treads and thresholds where falls actually happen.
Improve drainage and airflow
Water is not leaving the surfaceFalls corrected, gaps cleared, and the void beneath ventilated so the boards dry from both sides.
Re-deck in textured composite
The deck is shaded permanentlyTextured, grooved composite is far more forgiving in a shaded, damp garden.
Get this fixed properly
Free site visit across London and Hertfordshire, a written specification and a fixed price before anything starts.
Prevention
- Sweep leaves off through autumn rather than in spring
- Keep grooves and gaps clear so water drains
- Cut back overhanging planting to let sun and air onto the boards
Frequently asked
Is composite decking slippery?
Textured grooved composite generally grips better than smooth boards, but any deck slips if algae is left to build up.
Can I pressure wash the deck?
Carefully, at low pressure with a wide fan. High pressure tears softwood grain and makes the surface worse.
Do anti-slip strips look bad?
On steps they are barely noticeable and they are the single most effective safety upgrade.
Can you replace only the shaded section?
Yes, though matching board colour to a weathered deck is imperfect.