Slip and trip hazards in patios and driveways: causes and fixes

This is general information about common paving hazards, not a substitute for a professional inspection if you have concerns about a specific surface.

A patio or driveway doesn’t need to look dramatically damaged to be a genuine trip hazard. A slab that’s settled by a centimetre, a patch of algae that never quite dries out, or a joint that’s opened up slightly are all common and all fixable, but only if you know to look for them before someone catches a foot or a wheel. If you’ve already spotted a problem, local paving repair specialists can usually tell within a short site visit whether it’s a clean or a proper fix.

What actually causes the problem

Algae and moss. Shaded, damp areas that don’t get much direct sun, especially north-facing patios or spots under trees, are prone to a green film building up on natural stone and concrete. It’s slippery when wet and gets worse through autumn and winter when surfaces stay damp for longer.

Settled or sunken slabs. When the sub-base underneath a slab compacts unevenly, whether from poor original preparation, tree root movement, or ground settling over time, the slab above dips slightly and creates a step where there shouldn’t be one.

Cracked or spalling surfaces. Freeze-thaw cycles can cause the surface of natural stone or concrete to flake or crumble (spalling), creating an uneven, sometimes sharp-edged surface that’s both a trip risk and prone to holding water that then freezes.

Loose or missing joint material. Block paving with worn-away jointing sand can develop small gaps that shift underfoot, and while individually minor, enough of them across a surface make it feel unstable to walk on.

Hazard	Typical cause	Usual fix
Slippery surface	Algae or moss build-up in shaded areas	Clean with a stiff brush or pressure wash
Trip step between slabs	Settled or sunken sub-base	Lift and relay the affected slab
Crumbling surface	Spalling from freeze-thaw damage	Replace the affected area
Loose or shifting blocks	Worn jointing sand	Re-sand or re-point the joints

When it’s a clean-and-monitor job versus a repair job

Light algae is a cleaning job, not a repair. A stiff brush and a diluted patio cleaner, or a careful pressure wash on natural stone, usually sorts it out for a season. A genuine height difference between slabs, roughly a centimetre or more, is a different matter and worth having assessed, since that’s enough to catch a foot, a wheelchair wheel, or a pushchair.

Why patch repairs usually make more sense than a full relay

Most of these problems are localised. A sunken slab, a cracked section, or a patch of worn jointing doesn’t mean the whole surface has failed, and a contractor can typically lift and correct just the affected area rather than relaying the entire patio or driveway. That keeps cost and disruption proportional to the actual problem instead of treating a small issue as though it were a bigger one.

It’s worth having the whole surface looked at even when only one spot is bothering you, though, since a sub-base problem in one area sometimes shows up nearby before it’s visually obvious. A contractor can usually tell the difference between an isolated issue and an early sign of something more widespread.

Preventing the problem coming back

Once a hazard’s been fixed, a little routine seasonal upkeep keeps it from recurring. Cutting back overhanging branches that keep a patch shaded and damp, clearing leaves before they mat down over winter, and a seasonal check for any new dips or cracks all cost far less time than dealing with a hazard that’s been left to develop for a year or two unnoticed.

Getting an uneven surface checked

If you’ve noticed a trip hazard developing, don’t wait for it to get worse, particularly anywhere elderly family members or young children walk regularly. Start from the directory homepage to compare contractors, and check our scoring method for how we weigh completeness and workmanship in local ratings.