How to Clean Moss and Algae from Tiles and Walls

To clean moss and algae from tiles and walls, start by scraping and brushing off what comes away, apply an anti-algae and moss product, leave it to work and rinse with water. Repeat if necessary. Then deal with the cause, which is almost always damp and shade.

Why moss appears

Moss and green algae film grow where there is damp, shade and little air circulation. That is why they show up more on north-facing walls, in courtyards with trees, on steps and in places where water sits.

In winter, with rain and short days, surfaces take a long time to dry. As a result, algae spread quickly.

Cleaning step by step

Choose a dry day and protect nearby plants and lawn.
Sweep and scrape off the loose moss with a scraper or stiff-bristle brush.
Apply the anti-algae and moss product, following the instructions on the packaging.
Leave it to work for the time stated, without letting it dry out completely.
Scrub with a brush and rinse with plenty of water.
Repeat on the more stubborn areas.
Let it dry well before painting or sealing.

Taking care with the products

These products are strong. Wear gloves, safety glasses and clothes you do not mind getting dirty. Always read the label and test a small area first, because some products can change the colour of certain stones and renders.

Do not mix different products, because this can release dangerous gases.
Protect plants and avoid letting the liquid run off into the garden soil.
Keep children and pets away until everything is dry.
Rinse well, so as not to leave residue on surfaces that people walk on.

What about pressure washing?

Pressure washing cleans quickly, but it has risks. On soft stone, weak render or old joints, it can tear out material and leave the surface rougher, which makes it easier for moss to come back. Use low pressure and test in a corner first.

On paving, steps and ramps, wet moss is very slippery. Clean with care and do not use the surface until it is dry.

How to stop it coming back

Cleaning without dealing with the cause only works for a short time. Find out where the damp comes from and what keeps it there.

Prune tree and shrub branches to let in light and air.
Check gutters and downpipes, so that water does not run down the wall.
Make sure the paving has some slope so that water drains away.
Clean regularly, before the moss takes hold.
On painted walls, choose paints with protection against algae and mould.

When it is time to paint

If the wall is badly marked by stains, once it is clean and dry it can be primed and painted with paint made for exterior use. In high areas, such as eaves and roofs, do not climb up without equipment. For those jobs, hire professionals.

Tip: Clean in late spring or early autumn, on a dry, overcast day. The wall dries slowly, the product works better and there is less risk of stains from fast drying.