Concrete roofing tile

Why the surface matters more than on clay[edit]

A concrete tile's colour comes partly from pigment through the body and partly from an applied surface finish. That finish weathers, and as it does the tile fades and its surface becomes more open and more absorbent.

A faded concrete roof therefore looks dirty when it is mostly worn, and cleaning does not return the colour, because the colour has gone rather than been covered. This is the single most common misunderstanding a homeowner brings to a concrete roof, and it is the reason coatings are marketed hardest at this covering.

Cleaning considerations[edit]

The applied finish is the part that protects the body from absorbing water, so removing it accelerates exactly the weathering that made the tile look tired. High-pressure water will remove it, and on a tile already part-way through its life the difference between removing growth and removing surface is small.

A cleaned concrete roof that looks patchy afterwards is often a roof where the finish survived in some areas and not others, which is a result of the cleaning rather than of the growth that preceded it.

Age[edit]

Concrete tiles from the middle of the twentieth century onwards vary in quality and in how well the finish has held. A roof of forty or fifty years may have very little applied finish remaining, in which case the question is not how to clean it but whether cleaning achieves anything the owner wants.