Is soft washing safe for flat concrete tile?

Eagle Roofing Products makes concrete roof tile, and its 2019 and 2020 articles on cleaning a concrete tile roof are the maker's instructions this answer tests. A flat tile made of concrete is the material those articles are about, so nothing in them has to be adapted to a different surface before it applies.

Eagle is plain about the growth itself. It writes that the algae, mold and mildew on concrete tile are biological pollutants that “are not harmful to the integrity of the tile,” and that “concrete tile roofs are exceedingly cleanable.” The limits that follow are about how the cleaning is done, and there are three of them: the water, the cleaner, and the chemistry risk Eagle names.

One boundary comes first. Eagle is one maker. A low-profile tile or a flat tile made by another company takes its cleaning limits from that company, and where those limits differ, the tile's own maker is the one to follow.

Eagle's 2019 article recommends only water for a tile roof cleaning, with the water pressure never exceeding 1200 psi. Its 2020 article repeats both halves: water alone, and pressure no higher than 1200 psi.

What that number is and is not, for a soft wash in particular, is read under a safe pressure for a concrete tile roof, and why it stays with concrete tile is set out where each roof material keeps its own number.

A soft wash relies on a cleaning solution rather than on pressure, so on a flat concrete tile Eagle's second limit, the one on cleaners, is the one that governs it.

Eagle's 2019 article allows a cleaner when the roof calls for one: “Depending upon how dirty a roof appears and what pollutant is on the roof, it may be necessary to use a cleaner in conjunction with the pressurized water, but only in the most diluted solution possible.” The 2020 article adds that chemicals should be used sparingly.

No association or maker read for this answer publishes a sodium hypochlorite percentage for soft washing, so Eagle's “most diluted” line is the limit in print for this roof. A mix published for asphalt shingle is a different document for a different roof, which is the case made under whether tile and shingle can share one solution.

Eagle gives its reason for the compatibility rule in the same breath as the rule: the cleaner “should be compatible with concrete as there are products that can affect the PH of the tile or even etch the surface.”

For a soft wash, which already keeps the pressure low, that sentence points the question at what is in the solution and whether it suits concrete. Eagle's lines appear beside those of the shingle and metal roofing bodies in the side-by-side cleaning limits for tile, shingle and metal.

A tile that already looks etched, cracked or broken is a condition question, and condition belongs to a roofing contractor rather than a cleaner. What the estimate conversation can use is the material: on the free estimate form, the project details field can name the roof as flat concrete tile, with its maker if it is known.

The walking rules for tile have a clause written for curved profiles: on high barrel and S tile, weight goes on the high points of adjacent tiles, as explained under soft washing barrel tile. A flat profile has no high points, so that clause has nothing to grip.

The line that does carry over is TRI Alliance's general one: “Step on the bottom three inches of the installed tile. This section is supported by the lapped tile beneath it, and weight is transferred through to the deck below.” Eagle's owner information points the same way, to the lower center area of the tile, with soft-soled non-slip shoes, and it adds that tile must not be used as a staging area or work platform.

TRI also keeps feet off hips and valleys, where specially cut tiles are more difficult to replace, and it sends the repair or replacement of a broken tile to a professional roofing contractor.