Sprinkler Arcs and Fertilizer Rust, Dissolved Instead of Blasted

Water Moves Dirt. It Does Not Dissolve Iron.

The orange in a sprinkler stain is not a layer of grime sitting on the slab. It is iron oxide lodged in the surface pores, so a stream of water passes over it the way rain does. The National Park Service's guidance on cleaning historic concrete says water and steam methods are typically not effective at removing staining, and that high-pressure water can erode the concrete surface. The Brick Industry Association tells cleaners to depend on the chemical reaction of the cleaner rather than brush scrubbing or sprayer pressure, and warns that high-pressure water can etch mortar joints and strip the outer face of brick for good.

So turning the pressure up removes the wrong material. The cement paste or brick face around the stain can wear away before the rust does, leaving a rougher, lighter spot with orange still in it. Rust comes out when a cleaner made for iron dissolves it, and the rinse that follows is gentle. On brick, BIA sets the limit at 400 psi measured at the nozzle tip unless the brick maker permits more.

The Right Cleaner at the Right Strength

Many rust removers are acidic. Oxalic acid is the one in the Portland Cement Association's rust method for concrete, and extension guidance warns that it is poisonous and corrosive; NIOSH lists eye burns among its hazards and calls for preventing skin and eye contact. The Brick Industry Association prefers proprietary cleaners made for iron stains over site-mixed solutions, because they are generally safer, easier to control and more consistent. Paver-care brands sell rust removers made without muriatic acid, and one brand's directions call for goggles and rubber gloves, a two-to-three-minute soak, a hard bristle brush and a thorough rinse, repeated until the stain dissolves.

The acid to keep off a property is unbuffered muriatic (hydrochloric) acid. BIA says it tends to cause further stains and damage mortar joints, and the National Park Service says strong acids such as hydrochloric and hydrofluoric damage concrete and are harmful to people, animals, site features and the environment. An acid cleaner is never mixed with bleach or ammonia.

The surroundings get as much attention as the stain. BIA notes that acid cleaners can pit metal frames and stain limestone or cast stone trim, and that cleaning chemicals can damage plants and grass, so nearby metal, glass and trim are covered and beds are soaked with clean water before and after. Stamped, colored or sealed concrete and natural stone get extra testing, since chemical treatments can bleach concrete, remove surface paste or etch aggregate. Clay brick pavers need their own product: BIA warns that some cleaners sold for polymeric sand haze are unbuffered muriatic acid and should not be used on clay pavers.

Stop the Source or the Orange Returns

A treated stain stays gone only if the iron stops landing there. PROSOCO's rust guidance says to adjust irrigation heads that spray across concrete and to sweep fertilizer off concrete before it dissolves, and extension advice says the same about sweeping iron fertilizer pellets off concrete after an application. For a home or business on a drinking water well, the Macomb County Health Department collects water samples at no cost (lab fees apply), and its partial chemical panel includes iron. Metal furniture and planters can simply be moved.

We point out the heads and fixtures behind the stain while we are there. Re-aiming a head or changing the watering schedule is work for you or your irrigation contractor, and an iron filter is work for a water treatment contractor. Our guides go further on prevention: hard water and sprinkler rust on brick, orange and black sprinkler stains on vinyl and oil and rust stains on driveways.