How to Remove Moss and Algae from a Concrete Driveway

Moss and algae are a fact of life on New Zealand driveways, especially in shaded, damp, or south-facing areas. The good news is that with the right approach, you can safely remove the growth yourself and take steps to keep it from coming back. Here's how to tackle the job properly.

Why Moss and Algae Grow on Concrete

NZ's humid climate — particularly in regions like Auckland, the West Coast, and Northland — creates ideal conditions for moss, algae, and lichen to colonise concrete surfaces. Shaded driveways that stay damp, poor drainage, and overhanging trees all make the problem worse. Beyond looking unsightly, moss and algae make concrete dangerously slippery, which is a real safety hazard. Addressing it promptly is worthwhile.

What You'll Need

• Stiff-bristled broom or scrubbing brush
• Garden hose or pressure washer
• Moss and mould killer (available from Bunnings or Mitre 10)
• Protective gloves, safety glasses, and old clothing
• Bucket and measuring jug
• Optional: concrete sealer for prevention

Step 1 – Clear the Surface

Start by sweeping away loose debris, leaves, and any thick clumps of moss with a stiff broom. This makes the cleaning product more effective by allowing it to reach the concrete surface directly.

Step 2 – Apply a Moss and Algae Treatment

There are several effective options:

Proprietary Moss Killers

Products such as Wet & Forget, Rapid Action Moss & Mould Killer, or similar concentrate-based treatments are widely available at hardware stores. Always follow the manufacturer's dilution and application instructions carefully. Most are applied with a watering can or garden sprayer.

Diluted Bleach Solution

A solution of one part household bleach to four parts water is a cost-effective option for algae and light moss. Apply it to the affected area, leave it to work for 15–30 minutes, then scrub and rinse thoroughly. Avoid letting bleach run into garden beds or stormwater drains — it can harm plants and aquatic life.

Sodium Percarbonate (Oxygen Bleach)

This is a more environmentally considerate alternative to chlorine bleach. It breaks down into water and oxygen, making it safer around plants and waterways. Mix according to the product instructions and apply generously.

Safety note: Always wear gloves and eye protection when handling cleaning chemicals. Work on a calm, dry day so the product isn't washed away by rain before it can work.

Step 3 – Scrub and Rinse

Once the treatment has had time to work, scrub the surface firmly with a stiff brush to loosen the dead moss and algae. Rinse thoroughly with a garden hose. For stubborn growth or large areas, a pressure washer (available to hire from most tool hire shops) will save considerable effort — use a fan-tip nozzle and keep the pressure moderate (around 1,500–2,000 PSI) to avoid damaging the concrete surface.

Step 4 – Treat Remaining Stains

Green or black staining that remains after cleaning is usually residual algae pigment embedded in the concrete. A second application of your chosen treatment, left for longer before scrubbing, will often lift it. For very stubborn staining, a dedicated concrete cleaner may help.

Step 5 – Prevent Regrowth

Cleaning is only half the job. To slow regrowth:

• Seal the concrete with a quality concrete sealer — this reduces the porous surface that moss and algae cling to. Products are available from PlaceMakers and hardware stores.
• Improve drainage so water doesn't pool on the surface.
• Trim overhanging trees and shrubs to increase sunlight and airflow.
• Apply a long-acting moss inhibitor (such as Wet & Forget) once or twice a year as a maintenance treatment.

Disposal of Waste Water

Be mindful of where your rinse water goes. Under NZ environmental rules, chemical-laden water should not be directed into stormwater drains that lead to waterways. Where possible, direct rinse water to a grassed or garden area away from drains, or check with your local council for guidance.

Comparing Cleaning Methods

When to Call a Professional

For most homeowners, moss and algae removal is a manageable DIY task. However, consider calling a professional driveway cleaner or driveway layer if:

• The driveway has significant cracking, spalling, or structural damage that needs assessment before cleaning
• You need large-scale pressure washing of a long or complex driveway
• You're considering resealing or resurfacing the driveway after cleaning
• The moss problem is being driven by poor drainage that requires earthworks or drainage work to fix

A qualified driveway professional can assess the underlying cause and recommend the best long-term solution. You can find experienced local driveway layers and cleaners on tradedirectory.co.nz.

Sources & Further Reading

• BRANZ – Maintenance of concrete surfaces
• WorkSafe NZ – Safe use of chemicals
• MBIE Building Performance – Building Code guidance
• Bunnings – Moss and mould treatment products
• Mitre 10 – Concrete care products