Slurry coat

The Tile Roofing Industry Alliance's Roof Maintenance Guide sorts concrete tile by when its color goes in.

Integral color goes in first: TRI describes “adding pigment into the body of the tile during the mixing stage.” The slurry coat comes after the tile has its shape, by “applying a concentrated slurry coat of pigment to the tile surface following extrusion and forming.” Pigment mixed through the body is part of the whole tile; a slurry coat is a layer on its face.

The guide then says how each ages. “Slurry-coated tile can oxidize and turn chalky before gradually wearing down to the concrete base,” while integral-colored tile, in TRI's account, lightens at most at the surface and holds its base color. Oxidize is the guide's verb for that change, and the word gets its dictionary treatment at oxidation; the chalky look belongs to the tile's own coat, not to the paint-film condition that chalking describes.

Tile makers use the phrase in their paperwork too. In an archived copy of Eagle Roofing Products' Florida warranty text, headed NOT AN ACTIVE WARRANTY, “topical slurry coating delamination” sits among the specific exclusions, beside color, efflorescence, carbonation and oxidation. What a particular roof's warranty says about its finish is in that tile maker's own text.

What darkens a tile roof and what colors it are two different layers, and a roof cleaning is aimed at the first.

TRI Alliance writes that “Mildew, algae and moss do not grow directly on tile but on the accumulation of dust and other organic materials that settle on tile,” and that the growth “can be treated to restore the original look.” On a slurry-coated tile, that settled film lies on top of the color coat.

The coat itself is a different matter. None of the tile documents behind this entry describes a cleaning as restoring a color coat after it oxidizes, chalks or wears thin. TRI keeps recoating and painting for a professional with concrete tile experience, and puts the cleaning, primer and coat in an order that the answer on a roof being coated or painted sets out.

Which finish a given roof carries, and whether its coat has changed, is not something to read from a page or a photograph. The roof's installation paperwork, the tile maker's product literature or a roofing contractor's inspection settles it, and Eagle's owner information sends inspection to “the original roofing contractor” first. A chalky look can have more than one cause, and the answer on why a roof looks chalky sorts them by material. Marks that turn out to be the tile itself get their own treatment in the answer on old tile stains, and the answer on whether a wash brightens the color of the tile covers what a cleaning uncovers on each finish.