The short version
The green film on slabs is mostly algae and moss, not limescale. Against it you need a brush plus the right cleaner, not acid. And crucially: on natural stone never use acid or high pressure, it destroys the surface for good.
Over winter many patios take on a grey-green veil: a mix of algae, moss and lichen that loves moisture. In spring you want it gone, ideally without hours of scrubbing and without damaging the surface. With the right approach both are doable.
More important than the choice of cleaner is what your patio is made of. Concrete and porcelain stoneware tolerate a lot, natural stone is sensitive. Settle that first and you save costly mistakes.
Identify the material first
It decides the method and the product. This overview keeps you on the safe side.
| Surface | Tolerates | Keep away from |
|---|---|---|
| Concrete, washed concrete | Brush, patio cleaner, moderate pressure | nothing critical, just spare the joints |
| Porcelain stoneware, ceramic | almost anything, very robust | coarse wire brushes (scratches) |
| Natural stone (sandstone, marble, travertine) | soft brush, mild stone cleaner | acid and high pressure, both etch or erode the surface |
| Wood, WPC | soft brush, special wood cleaner | high pressure (roughens the fibres) |
Removing green film, step by step
Sweep dry first
Sweep off leaves and loose dirt. A dry base lets the cleaner work better.
Wet & apply
Wet the surface, apply the cleaner and let it act per the instructions. Not in full sun, or it dries too fast.
Brush
Work in lanes with a firm but non-scratching scrubber. On natural stone use a soft brush.
Rinse clear
Rinse thoroughly with water so no residue stays in the joints. Let it dry, done.
The pressure washer, honestly judged
It is tempting, but not always the right choice:
- Natural stone and wood: the jet erodes and roughens the surface.
- Joints: high pressure flushes out the joint sand, then weeds grow all the more easily.
- If you must: only on concrete or porcelain stoneware, with a surface-cleaner attachment and at a distance.
When in doubt, brush and cleaner, gentler and longer-lasting.
What clears the green film
Against algae and moss on stone there are effective specialist cleaners, many on a mild basis. What to look for:
- Suitable for your surface (natural-stone-safe if needed)
- Chlorine-free if plants or animals are nearby
- With a long-term effect, which delays the next green film
Frequently asked
Can I use vinegar or citric acid against green film?
Is a pressure washer the fastest way?
How do I stop green film coming back fast?
Special cleaning made easy
The right product and method for every surface, honestly explained.
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