What is a safe pressure for a concrete tile roof?

Asked for a safe pressure on concrete tile, the documents read for this answer offer one sentence, from Eagle Roofing Products, a concrete tile maker, in its 2019 cleaning article: “If you decide it is time to have your tile roof cleaned, it is recommended that you use only water with the water pressure never exceeding 1200 pounds per square inch (psi).”

Each clause does its own work. “It is recommended” is Eagle's verb, a recommendation rather than a rule written for anyone else's tile. “Only water” is what Eagle recommends first. “Never exceeding” makes 1200 the top of what Eagle will accept, a ceiling rather than a number to aim for. Eagle's 2020 article repeats both halves, water only and a pressure that “should not exceed 1200 psi.”

The unit is spelled out in Eagle's own sentence, pounds per square inch, and what a psi figure means once it is separated from its surface is set out in the glossary.

Nothing in the documents read turns 1200 psi into the line a tile breaks at. The pressure figure sits in Eagle's cleaning articles. Eagle's warning about damage sits in a different document, and it carries no number.

That document is the owner information in Eagle's Florida limited warranty, which says: “Walking on or putting pressure on tiles can potentially cause damage. Our recommendation is to stay off your roof.” The warning is about weight on the tile, and it names no psi figure at all.

Reading 1200 psi as the pressure at which tile starts to crack joins two Eagle documents that Eagle kept apart. Whether a particular tile is cracked or broken is not a psi question either: TRI Alliance sends the repair or replacement of broken tiles to a professional roofing contractor.

Eagle places a second limit beside the pressure one. Where how dirty a roof is, or what pollutant is on it, calls for a cleaner, Eagle allows one only in the most diluted solution possible, and one compatible with concrete.

That limit is written as a direction, not a figure. Eagle publishes no product, ratio or strength for it, and no association or maker read for this answer publishes a sodium hypochlorite percentage for soft washing. The pressure ceiling and the cleaner limit are separate instructions, and neither one sets the other.

1200 psi is Eagle's figure for its concrete tile. It is not a shingle number or a metal number, and no roof pressure figure travels from one material to another.

The other roofing documents read for this answer handle pressure differently. ARMA and the Metal Roofing Alliance rule a pressure washer off asphalt shingle and metal, and Duro-Last publishes a different figure for its own membrane. The instructions for each material sit together in the maker-by-maker cleaning limits on the roof cleaning page.

The two Eagle articles quoted here name no tile profile, so they do not split the figure between barrel tile and flat tile. What the shape of a flat profile changes, and what it does not, is answered under soft washing flat concrete tile.

Eagle's 2020 article also says that specialists cleaning concrete tile “may use a high-pressure power washer sprayer,” in the same article that recommends water only and a pressure that should not exceed 1200 psi.

That sentence names equipment beside the ceiling, not a reason to run a job up to it, and it describes no particular company's equipment. Whether pressure washing a tile roof is a bad idea is a separate question, and so is why roof cleaners use low pressure at all.

Two other numbers are easy to confuse with this one. No trade association or roofing maker read for this answer publishes a psi figure that defines a soft wash, so 1200 psi is not a soft-wash number. And ICPI's 1,000 to 4,000 psi is a range for cleaning interlocking concrete pavers, not a roof figure.