Why does my roof look chalky?

The painted metal row is what the paint trade means by the word. U.S. Steel calls chalk “a natural white by-product of ultra-violet degradation of the paint system,” a film that “makes colors appear lighter and reduces the natural gloss of the original paint.” Sherwin-Williams defines chalking as “the formation of fine, white powder on the surface of the paint film due to weathering, which may give the appearance of color fading.” Both describe a paint film breaking down, and neither is describing tile.

U.S. Steel adds where chalk, the by-product of UV degradation, builds most: “Chalking increases with greater exposure to the sun,” and the roof, the south side of a building and buildings in southern climates may chalk more. It also notes that chalking on darker colors is more noticeable than on lighter ones.

The first is wear. TRI Alliance writes: “Slurry-coated tile can oxidize and turn chalky before gradually wearing down to the concrete base.” The coat wears away and the concrete base is what remains, and oxidation is TRI's word for the change that comes first. Integral-colored tile, by TRI's account, may show some surface lightening but keeps its base color.

The second is chemistry. TRI describes efflorescence on concrete tile as a temporary, superficial condition that can appear as “an overall chalky white bloom (softening of color) or in concentrated patches,” and says that in most cases carbon dioxide and rainwater gradually remove it. Eagle Roofing Products' Florida owner information describes temporary light patterning on darker tiles, caused by efflorescence, and says it “will disappear completely after additional exposure to rain.” What efflorescence is and how it forms is taken up under the white powder on roof tiles.

Color itself sits outside Eagle's warranty. Eagle's owner information, as archived, says “Eagle does not warrant color due to the tile exposure to the elements,” and that on single-color roofs some variation in hue from tile to tile is expected and tends to be less noticeable as the roof ages. A color question under a tile warranty goes to that tile maker's own warranty text.

The roof material narrows it, but on concrete tile a worn slurry coat and an efflorescence bloom can both read as pale and chalky from the ground. Which one is on a given roof is a question for a licensed roofing contractor who can get up close to the tile, not for anyone guessing from the driveway.

None of the documents quoted here presents a wash as the way to put a worn color coat back. TRI Alliance treats recoating or painting concrete tile as its own job for a hired professional, not as part of a cleaning, and where Florida's contractor statute places coating work is set out under where a cleaning stops and a roofing contractor starts. A cleaner does not inspect a roof or tell you its condition either, a point made plainly under what an exterior cleaner is not.

If the question behind the chalky look is really about age, whether age rules a cleaning out is answered under whether a roof can be too old to clean, and whether a cleaning changes how tile color looks at all is answered under whether roof cleaning brightens tile.