Should You Coat Your Roof After Cleaning?

For most houses, the answer is no, not as a matter of course. A cleaned roof that is in sound condition is in good shape without a layer on top. What it usually needs is a treatment that makes it harder for moss and algae to settle again, and that is a different product from a coating, with a different purpose.

A coating is a decorative and protective finish painted or sprayed over the tiles. The case for it is cosmetic wear: a faded or patchy roof that you want to look uniform again, or tiles whose surface has weathered enough that you would like to renew it. It is a considered extra, not a repair, much as a coat of paint is to a wall: it only looks right over sound plaster.

The cost and the future upkeep should shape your decision. A coating adds to the bill and, once applied, becomes something to maintain. If you are unsure, start with the clean and treatment, live with the result for a season and decide after. Nothing is lost by waiting, whereas a coating put over a roof with hidden faults hides the problem instead of solving it.

Consider one when the tiles are sound but visibly tired, the colour coat has worn through in patches and you intend to live there for years yet. A roof that is going to be sold soon might be a candidate too, if the aim is kerb appeal, though a clean often does most of that on its own.

It makes less sense when tiles are cracked, slipping or porous in a way that points to age. Painting over cracks does not mend them. Where a roof is approaching the point of replacement, the money is better spent on repairs or a re-roof, and the same logic applies where moss has been lifting the tiles.

Whatever the reason, the surface has to be properly clean and fully dry first, so the work cannot be squeezed into a wet week, and the biocide has to have done its job beforehand. If someone offers you a coating without a thorough clean, or without looking at the condition of the tiles, ask them to slow down. Our answer on how long roof biocide lasts shows what the alternative buys you.

Ask what product is going on, what it is for and how it is applied. A sensible roofer will also tell you what the tiles are made of and how old they look, since that shapes whether a finish would bond well. Ask what the manufacturer says about the type of tile on your roof, whether concrete, clay or something else, and how it behaves on a roof like yours. Ask how long the roofer expects it to last and what that is based on, remembering that a manufacturer's warranty and a lifespan are different things.

Ask what happens at the edges and overlaps, because a coating that bridges the gaps between tiles can interfere with the way water runs off. Ask what happens when a tile later needs replacing. A replacement in a coated roof will look different from its neighbours until it is treated to match.

Finally, ask for the price in one written total, with what it includes and whether VAT is added. Pictures taken at our inspection let you see the tiles for yourself before deciding. Keep them: a before-and-after record is useful if you ever sell the house or need to show what was done. For the full discussion, including materials and drawbacks, read our guide to roof tile coating.

Start with the clean. It shows you what the roof is really like, because moss hides cracks, slipped tiles and worn flashings. Once the surface is clear, the roofer can tell you honestly whether a coating would add anything or whether the spend would be better directed elsewhere.

Then protect against regrowth in the simplest way. Keep the gutters clear, trim overhanging branches and let the sun and wind dry the slopes. These cost very little and do much of the work that a coating claims to.

If the clean reveals problems, deal with them in order: repairs, then treatment, then any cosmetic finish. A roofer who pushes the last item before the first is putting the sale ahead of the roof. The overview of cleaning and treatment is on our roof cleaning and moss removal page, and the chemistry of the treatment is explained in how biocide roof treatment works.