How to Reduce Slip Hazards Caused by Moss, Mould and Algae

Slippery outdoor surfaces are a common safety concern around New Zealand homes, particularly during the wetter months. Moss, mould and algae can reduce grip on paths, steps, decks and driveways, increasing the risk of slips and falls if left untreated.

These growths often develop gradually, so the risk is not always obvious. A thin green film on concrete, dark patches on timber or moss between pavers can all make outdoor surfaces more difficult to walk on safely, especially after rain or heavy dew.

This guide explains where slippery organic growth commonly develops, the warning signs to look for and practical ways to help reduce slip hazards around your property.

Why Slippery Outdoor Surfaces Matter

Outdoor surfaces are exposed to rain, shade, leaf litter and changing temperatures. When moss, algae or mould begin to grow, they can hold moisture and create a slick layer over the surface.

This can be a concern for:

• Household members
• Older visitors
• Children
• Delivery drivers
• Tradespeople
• Tenants and customers

The risk may be greater on sloping, narrow or frequently used areas where there is less room to recover if someone loses their footing.

Outdoor Areas You Should Check Regularly

Outdoor Area	What to Watch For	Why It Matters
Front steps	Green algae, moss along edges and damp corners	Reduced grip on a high-traffic entry point
Concrete paths	Thin green film, dark staining and persistent dampness	Can become slippery after rain or morning dew
Timber decks	Dark mould patches, algae beneath furniture and damp boards	May reduce traction, particularly when wet
Sloping driveways	Algae film and moss in shaded sections	Sloping surfaces can be harder to walk across safely
Pavers	Moss and algae between joints	May create both slippery and uneven footing
Pool surrounds	Constant dampness, algae and shaded patches	Bare feet and wet surfaces increase the need for good grip
Outdoor ramps	Green growth, moisture and leaf build-up	Reduced traction may create an access concern

Front Entrances and Steps

Front entrances are used every day and are often one of the first places where moss and algae become a safety concern.

Steps beside gardens, beneath roof overhangs or on the shaded side of the home may stay damp long after rain has stopped. Moss can also build up along the edges, where it may be harder to notice.

Check:

• The front step and landing
• Handrail areas
• Edges of concrete steps
• Paths leading from the gate or driveway
• Areas beneath trees or verandas

If a surface feels slick underfoot or looks green when wet, it is worth addressing before the build-up becomes heavier.

Paths and Walkways

Paths beside the house, through the garden or between buildings often receive limited sunlight and airflow.

Morning dew, runoff and leaf litter can keep these areas damp, allowing algae and moss to spread across the surface.

Pay particular attention to:

• Narrow side paths
• Garden walkways
• Paths used by delivery drivers
• Walkways near downpipes
• Areas where water regularly pools

Sweeping away leaves and improving drainage can help, but established organic growth may also need treatment.

Timber Decks and Outdoor Living Areas

Timber decks can become slippery when algae and mould develop on the boards.

This often happens:

• Beneath outdoor furniture
• Under trees
• Near planters
• On shaded sides of the house
• Where leaves and moisture collect between boards

Because decks are commonly used for entertaining, inspect them before gatherings, during winter and after long periods of rain.

Dark patches, green staining or boards that remain damp for a long time may indicate that cleaning or treatment is needed.

Driveways and Vehicle Access Areas

Driveways are often thought of as vehicle surfaces, but they are also used by pedestrians, couriers and visitors.

A sloping driveway with algae growth can become difficult to cross safely in wet weather.

Check:

• Shaded edges
• Areas near retaining walls
• Sections beneath parked vehicles
• Runoff channels
• Paths connecting the driveway to the house

Reducing moss and algae build-up can help improve both appearance and day-to-day access.

Pool Areas, Courtyards and Patios

Pool surrounds and outdoor entertaining areas are regularly exposed to water, shade and foot traffic.

Even surfaces designed for outdoor use can become slippery when covered by algae or mould.

Watch for:

• Green film around pool edges
• Moss between pavers
• Dark growth beneath outdoor furniture
• Persistent dampness near drains
• Leaf build-up in corners

These areas should be checked regularly because people may be walking barefoot or moving quickly across them.

Warning Signs You Should Not Ignore

Organic growth does not always look thick or obvious. Some of the earliest warning signs are easy to miss.

Look for:

• A thin green film that becomes more visible when wet
• Black or dark patches on timber or concrete
• Moss growing along step edges
• Persistent dampness after surrounding areas have dried
• Slippery patches beneath outdoor furniture
• Growth returning quickly in the same shaded area
• Moss developing between pavers or along cracks

If an area feels more slippery than usual, inspect it even if the growth is not immediately obvious.

Seasonal Outdoor Safety Checklist

Regular inspections can help you deal with small patches before they become widespread.

• Inspect steps and paths before winter
• Check shaded areas after prolonged rain
• Sweep leaves and organic debris from decks and paving
• Clear blocked drains and downpipes
• Trim vegetation to improve sunlight and airflow
• Check outdoor areas before guests or tenants arrive
• Inspect ramps and sloped access routes regularly
• Treat small patches before growth spreads

Who Is Most at Risk?

Anyone can slip on moss, mould or algae, but some people may be more affected by reduced grip on outdoor surfaces.

This includes:

• Older adults
• Young children
• Visitors who are unfamiliar with the property
• Delivery drivers and couriers
• Tradespeople carrying tools or equipment
• Anyone carrying heavy items or using outdoor steps during wet weather

Inspecting high-traffic areas regularly and treating slippery growth early can help reduce risks for everyone using the property.

Why Early Treatment Matters

Moss, mould and algae are usually easier to manage when the affected area is still small.

Early action can help:

• Reduce slippery organic build-up
• Keep frequently used areas easier to walk on
• Make regular maintenance more manageable
• Help prevent small patches from spreading across a larger surface
• Improve the appearance of outdoor areas

Treatment does not immediately make a wet surface safe, so access should still be restricted until the area is dry and the growth has broken down.

Practical Ways to Reduce Slip Hazards Around Your Property

Reducing slip hazards involves more than treating visible moss and algae. Regular maintenance and early intervention can help keep outdoor areas safer throughout the year.

• Inspect paths, steps and decks regularly, particularly during autumn and winter.
• Sweep away leaves and organic debris that trap moisture.
• Trim overhanging trees and shrubs to improve sunlight and airflow.
• Repair drainage problems that leave surfaces damp for long periods.
• Treat moss, mould and algae before they become widespread.
• Keep outdoor lighting in good working order so slippery areas are easier to see at night.
• Restrict access to treated areas until they are dry.
• Inspect high-traffic areas after heavy rain.

Combining good property maintenance with a suitable moss and mould treatment can help reduce slippery organic growth and make outdoor areas easier to use safely.

Using Spray & Go as Part of an Outdoor Safety Plan

Spray & Go Moss & Mould Commercial 5L can form part of an ongoing outdoor maintenance plan. By treating moss, mould, algae and lichen on suitable exterior surfaces, it can help reduce slippery organic growth before it becomes more widespread.

The product is designed as a spray-and-leave treatment, allowing the growth to die back gradually while natural weathering helps remove the residue.

Always:

• Read and follow the product label
• Use the recommended dilution rate
• Patch test unfamiliar or coated surfaces
• Keep children and pets away during application
• Restrict access while surfaces remain wet
• Use safe access methods for roofs or elevated areas

For full application guidance, read our guide on how to remove moss, mould and algae from outdoor surfaces with Spray & Go Commercial.

For information about compatible surfaces and areas requiring extra care, see our Spray & Go surface safety guide.

Frequently Asked Questions

Why do outdoor paths become slippery?

Paths can become slippery when moss, algae and mould form a thin layer over the surface. Moisture, shade, poor drainage and organic debris can all contribute to this growth.

Which areas around the home are most likely to become slippery?

Front steps, shaded paths, timber decks, sloping driveways, pool surrounds, pavers and outdoor ramps are among the areas most likely to develop slippery growth.

Can algae make concrete slippery?

Yes. Algae can create a slick film on concrete, particularly after rain or in areas that remain shaded and damp.

Can mould make timber decking unsafe?

Mould and algae may reduce grip on timber decking, especially when the boards are wet. Inspect shaded sections and areas beneath furniture regularly.

Should I pressure wash slippery moss and algae?

Pressure washing may not be suitable for every surface and can sometimes damage coatings, timber or roofing materials. Check the surface manufacturer’s guidance and consider a suitable spray-and-leave treatment where appropriate.

When should I inspect outdoor surfaces?

Inspect outdoor surfaces before winter, after prolonged rain, before entertaining and whenever you notice dampness, green staining or reduced grip.

Does treating moss make the surface safe immediately?

No. Treated growth may remain slippery while the product is working. Keep people and pets away until the area is dry and continue to use caution until the growth has broken down.

How can I help stop moss and algae returning?

Improve drainage, remove leaves, trim nearby vegetation, increase airflow and sunlight where practical, and inspect affected areas regularly.

Can Spray & Go be used on concrete paths and driveways?

It may be used on suitable concrete surfaces according to the product label. Patch test unfamiliar finishes and follow all application and safety directions.

Is slippery moss more common during winter?

Yes. Moss, mould and algae often grow more quickly during cooler, wetter months when outdoor surfaces remain damp for longer. Regular inspections during autumn and winter can help identify slippery areas before they become a larger problem.

Help Keep Outdoor Areas Safer with Pestrol

Slippery paths, steps, decks and driveways can become a safety concern when moss, mould and algae are left to build up. Regular inspections, good property maintenance and early treatment can help reduce slippery outdoor surfaces throughout the year.

If you have noticed moss, mould or algae around your home, view Spray & Go Moss & Mould Commercial 5L to learn more about treating suitable outdoor surfaces.

You can also read our related guides:

• How to Remove Moss, Mould & Algae from Outdoor Surfaces with Spray & Go Commercial
• Where Can You Use Spray & Go Moss & Mould Commercial? A Surface Safety Guide