Concrete Tile Roof Cleaning

Why concrete tiles grow so much moss

Concrete tiles have a textured surface that holds moisture and gives spores a foothold. Over time the factory surface coating weathers, leaving the tile more porous still. North-facing slopes and pitches shaded by trees stay damp longest and usually carry the heaviest growth.

The deep profile of many interlocking tiles creates channels and overlaps where moss settles and builds into cushions. Left alone, those cushions hold water against the tile and can lift at the edges, sending clumps into the gutters.

Why we never pressure wash concrete tiles

A pressure washer will make a concrete roof look clean quickly, but it does so by blasting at the surface. That can strip the remaining surface coating, erode the tile, drive water up under the laps and into the roof space, and dislodge pointing on ridges and verges. A rougher, more porous tile then tends to green over again sooner.

One of our customers mentioned having been told previously to avoid jet washing; physically scraping the moss off was the approach they valued. That is how we work on concrete roofs.

How a concrete tile roof is cleaned

Heavy moss is removed by hand, working with the direction of the tiles so edges are not levered up. Loose material is cleared from the surface and valleys, and the gutters below are cleared afterwards so the debris does not cause a blockage. Where suitable, a soft wash and biocide are then applied to deal with remaining algae and lichen and slow regrowth.

The exact approach depends on the roof's condition. A roof with cracked or slipped tiles may need a repair conversation before cleaning.

Ridges, verges and pointing

Concrete tile roofs are often finished with mortar-bedded ridge tiles and verges. Old mortar can be cracked or loose, and careless cleaning can finish it off. We look at the ridge and verge condition while cleaning and tell you if anything has deteriorated.

If repointing or replacing a slipped tile is needed, it can be quoted separately. Our roof repairs page explains the minor roofing work we carry out.

Faded colour versus growth

Not all discolouration on a concrete roof is moss. Concrete tiles naturally lose some of their colour with age as the surface weathers. Cleaning removes growth and dirt, revealing the tile beneath, but it will not restore the original factory colour of a tile that has faded.

Lichen can also leave marks after it has been treated, which fade gradually rather than disappearing on the day. We explain what to expect from your particular roof before work starts.

Is a concrete roof worth cleaning?

For a structurally sound roof, removing moss stops it holding water against the tiles and clogging gutters, and it improves the look of the house considerably. Concrete tiles are generally robust, and many roofs simply need the growth dealt with rather than replacing.

If tiles are crumbling, widely cracked or the roof is near the end of its life, cleaning is not the answer, and we will say so. Our guide comparing roof cleaning with replacement covers this decision in more detail.

What to send for a concrete roof quote

Photographs of each roof slope from the ground, ideally from the garden and the road, show us where the moss is heaviest. Include close-ups of valleys and ridges if you can take them safely, and note any tiles you can see are cracked or slipped.

Tell us the height of the property, whether there is a conservatory or extension roof below, and how each side can be reached. We will then explain the approach for your roof and give a free quote.

Bungalows and estate houses

Concrete tiles are especially common on bungalows and post-war estates, where long, low roofs can carry a lot of moss on the shaded side. A bungalow roof clean usually pairs naturally with clearing the gutters below.