Sick of the Green Slime?
Algae grows fast and makes your patio dangerously slippery. Our treatment kills it quickly and leaves a protective barrier that stops it coming back.
That slimy green film on your patio isn’t moss. It’s algae, and it’s one of the most common complaints from UK homeowners, especially during the wetter months.
Algae might look less dramatic than thick moss growth, but it’s actually more dangerous. That thin green coating becomes incredibly slippery when wet, turning your patio into an ice rink every time it rains.
The good news? Algae is easier to remove than moss or lichen. The bad news? It grows back faster too. Here’s how to deal with it properly.
Algae vs Moss: What’s the Difference?
Before you start treatment, it helps to know exactly what you’re dealing with. Algae and moss look similar at a glance, but they behave differently.
Algae forms a thin, flat coating on surfaces. It doesn’t have leaves or structure you can see with the naked eye. When wet, it feels slimy and slippery. When dry, it might look like a green or black stain.
Moss is three-dimensional and fluffy. You can see individual plants with tiny leaf-like structures. It forms cushions and clumps rather than a flat film.
Why does this matter? Algae grows much faster than moss. A patio can go from clean to green in just a few weeks during mild, damp weather. It also responds more quickly to treatment, but will return faster if conditions stay favourable.
If you’re not sure what you’ve got, our guide to moss vs algae vs lichen explains the differences in more detail.
Why Your Patio Gets Algae
Algae needs three things: moisture, nutrients, and a surface to grow on. UK patios provide all three in abundance.
Moisture is the big one. Algae can only grow when there’s water present. Patios that stay damp for extended periods, whether from rain, poor drainage, or shade that prevents drying, are algae magnets.
Nutrients come from organic matter. Fallen leaves, bird droppings, soil splashed up from beds, even airborne dust all provide food for algae. The more organic debris on your patio, the faster algae will grow.
The surface itself just needs to hold moisture long enough for algae to establish. Textured stone, rough concrete, and porous materials are more susceptible than smooth, sealed surfaces.
The Slip Hazard Problem
Let’s be clear about why algae matters: it’s a genuine safety issue.
Dry algae provides reasonable grip. But the moment it gets wet, it becomes treacherously slippery. A thin coating of wet algae on paving is more dangerous than ice because you can’t always see it coming.
This is especially concerning on steps, slopes, and high-traffic areas. Falls on hard paving cause serious injuries, and algae-related slips are surprisingly common.
If your patio is currently covered in algae and it’s wet outside, treat it as a hazard. Scatter sand or grit for temporary grip while you wait for treatment to work.
How to Remove Algae from Your Patio
You’ve got several options depending on how much algae you’re dealing with and how quickly you need results.
Method 1: Scrubbing with Soapy Water
For light algae coverage, sometimes elbow grease is enough.
Mix warm water with a squirt of washing up liquid in a bucket. Scrub the affected areas with a stiff bristle brush, working the soapy water into the surface. Rinse thoroughly with clean water.
This removes surface algae and improves grip immediately. The downside? It doesn’t kill the algae at a cellular level, so regrowth happens quickly. You’re cleaning the surface rather than treating the problem.
Washing up liquid helps loosen the algae but isn’t actually toxic to it. Think of this as a temporary fix rather than a solution.
Method 2: Pressure Washing
A pressure washer will blast algae off faster than scrubbing. It’s satisfying and effective for removal, but comes with caveats.
High pressure can damage softer stones like sandstone and limestone. It can also blast out pointing between slabs and etch the surface of some materials.
If you pressure wash, use the lowest effective pressure and keep the nozzle moving. Don’t focus on one spot. And be aware that pressure washing alone does nothing to prevent regrowth. You’ll be back with the washer again in a few weeks.
For best results, combine pressure washing with a preventative treatment afterwards.
Method 3: Algae Killer Treatment
The most effective approach is using a product designed to kill algae and prevent regrowth.
Apply the treatment to dry paving using a pump sprayer or watering can. Make sure you get even coverage across all affected areas. Most treatments need time to work, so don’t rinse off.
Within a week or two, the algae will die and can be swept or brushed away. The treatment continues working after application, creating a hostile environment for new algae growth.
This is more effort than a quick scrub, but the results last much longer. One proper treatment can keep algae at bay for months rather than weeks.
Method 4: Household Alternatives
If you prefer not to use dedicated products, some household items can help.
Bleach kills algae effectively but can discolour paving and damage nearby plants. Dilute heavily (one part bleach to ten parts water) and rinse thoroughly after treatment.
Vinegar is less harsh but also less effective. It may work on thin algae films but struggles with heavier coverage.
Boiling water kills algae on contact but offers no ongoing protection and is impractical for large areas.
None of these match a proper algae treatment for convenience and lasting results, but they’re options if you want to use what you already have.
Preventing Algae Coming Back
Removal is pointless if the algae returns within weeks. Prevention is where you really save time and effort.
Improve drainage wherever possible. If water sits on your patio after rain, look at whether you can adjust levels or clear blocked drains. Even small improvements help surfaces dry faster.
Reduce shade if you can. Cutting back overhanging branches and shrubs lets more sun and air reach the paving. Algae struggles in conditions where surfaces dry quickly.
Keep the patio clean. Regular sweeping removes the organic matter that algae feeds on. Clear fallen leaves promptly in autumn, and brush away any soil or debris that accumulates.
Apply preventative treatment. A light application of algae killer in spring and autumn, when conditions favour growth, stops algae establishing before it becomes visible.
Different Patio Materials
The treatment approach is similar across materials, but some need extra care.
Concrete is tough and tolerates most cleaning methods including pressure washing. It’s also porous, so benefits from preventative treatment.
Block paving has lots of joints where algae loves to grow. Pay attention to the gaps as well as the block surfaces.
Natural stone varies hugely. Hard granite can handle aggressive cleaning. Soft sandstone and limestone need gentler treatment to avoid damage.
Porcelain and ceramic tiles are less porous and resist algae better, but can still get slippery films in shaded areas.
Our moss removal methods explained guide covers treatment for all common patio materials.
When Algae Keeps Returning
If you’re treating your patio regularly but algae keeps coming back quickly, the underlying conditions are too favourable.
Consider whether structural changes might help. Installing better drainage, removing a tree that casts permanent shade, or even replacing paving with a less porous material might be worth the investment if you’re spending hours on cleaning every few months.
For chronically shaded, damp patios, more frequent preventative treatment may be the only realistic solution. Three or four applications per year is more effort than ideal, but still less than constantly scrubbing green slime.
Ready to reclaim your patio? Stop scrubbing every few weeks and get lasting results. Our Moss, Mould & Algae Killer clears algae and keeps it away so you can actually enjoy your outdoor space.
