Question answered
Cleaning concrete roof tiles
The short answer
Concrete roof tiles can be cleaned safely, provided the method is gentle. Moss is scraped or brushed off by hand and a biocide is used to kill what remains, with low-pressure rinsing only where it suits. Hard pressure washing can strip the tile's surface and open it to water, so the aim is a clean roof with the face of every tile intact.
Concrete tiles cover a great many Sussex roofs and they take moss readily. They also have a surface that can be worn away, so the way a clean is done counts for more than the decision to do it.
Why concrete tiles grow moss so easily
A concrete tile is a porous material. Its surface holds a little moisture, and the grit and dust that settle on it feed spores blown in from trees, walls and neighbouring roofs. Where a slope stays damp, growth gets a foothold in the small hollows and along the edges of each tile.
The shape of the tile helps moss too. Interlocking profiles have ridges and channels where water slows down, and the overlapped edge between one tile and the next is a sheltered spot where a green line often begins.
Shade and shelter make it worse. A slope under trees, a roof on the north side of a house, or a lower roof that collects leaf litter will carry moss sooner than a sunny, open slope. Younger roofs show it later, but the process is the same. Moss then holds water against the tile, so a patch that starts small keeps its own surroundings damp and spreads. Left alone for a few seasons, it can cover whole courses.
The surface coat and why pressure is risky
Many concrete tiles carry a thin surface layer that gives them colour and a smoother face. It sits on top of the body of the tile and is not meant to be scoured. Strong jets can remove it in places, leave the tile paler and rougher, and expose more of the porous material underneath.
A rougher tile holds moisture and growth more readily, so aggressive cleaning can bring moss back faster than it would have returned on an untouched roof. MyBuilder's roof cleaning guide, updated on 21 August 2026, says pressure washing may damage delicate tiles, a fair warning for any tile with a worn face. Colour can also fade unevenly after rough cleaning, which is hard to reverse.
Jets can also push water sideways under the laps, past the underlay and into the loft. Our page on roof cleaning and moss removal compares the main approaches and when each is a sensible tool.
Gentler methods that suit concrete
The usual approach starts by hand. A stiff brush or a flat scraper lifts the thick moss without touching the tile face, working down from the ridge so that debris moves towards the gutter. The roof is then treated with a biocide, which kills the roots, spores and lichen that scraping leaves behind.
A low-pressure rinse can follow where the tiles are sound, used to carry loosened residue away rather than to blast anything off. The treatment does the cleaning work over the following weeks, as the dead growth lets go and washes down in the rain.
This is slower than a jet wash, but it protects the tile, and protecting the tile is the point. Where a tile is already crumbling, flaking or cracked, cleaning is paused until it is replaced, because a loose piece can slide under foot or take on more water once its cover of moss has gone.
Moss, gaps and what the survey looks for
Before any cleaning starts, we look at the roof as a whole. Moss can hide cracked tiles, slipped tiles and failing mortar at the ridge, and cleaning can loosen a tile that was only being held in place by growth. Finding those faults first means they are repaired before water finds them.
We also check the lead and flashings, the valleys and the gutters. Heavy moss often sits in a valley or along the eaves where it can block the flow of water. Our article on moss blocking gutters explains how a small patch becomes an overflow.
Survey photographs show you the condition of each slope, and you receive the quote in writing as one figure. If a clean would only hide a failing roof, we recommend the repair first and the clean afterwards.
Keeping a cleaned concrete roof clean
Cleaning is not a permanent cure, because moss will find a damp, shaded slope again. What helps is removing the cause where you can: trim back overhanging branches, keep gutters flowing, and clear leaf litter from valleys and lower roofs.
A fresh biocide treatment is sometimes repeated at intervals, depending on how fast your roof regrows. Some owners prefer a longer gap and accept a faint green tint on a shaded slope. Neither choice is wrong, so long as the gutters stay clear and the tiles remain sound. A look from the garden each spring and autumn, with binoculars if you have them, shows which slope is turning green first.
Concrete tiles often last 30 to 60 years, going by MyBuilder and Marley, and gentle care helps a roof reach the upper end of that range. If you are planning around a sale, how long a roof clean takes will help with dates.
Concrete tile cleaning, briefly
Will cleaning make my concrete tiles leak?
A gentle clean should not. Leaks follow when jets drive water under the laps, or when cleaning exposes an old crack or slipped tile that moss was covering. That is why the roof is inspected first, and why loose or broken tiles are replaced before any treatment goes on.
Can I paint or coat concrete tiles after cleaning?
Coatings exist, but they are a separate decision from cleaning. A coating needs a clean, dry and sound surface, and it will not mend a failing tile. Ask any supplier what maintenance it needs and what happens at the first sign of wear.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
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