Maintaining a like-new finish on galvanized steel requires attention to two sets of activities. The first is preventing build-up on galvanized steel, and the second is removing build-up without damaging the zinc coating or the steel beneath it.
Preventing Build-Up on Galvanized Steel
The most important step in preventing corrosion on galvanized steel is keeping it out of environments where it is exposed to substances with a pH below 6 or above 12.
One side of this requirement is that it is important to keep galvanized steel out of acid rain. Ordinary rain has a pH of 5 to 6, which damaging if the steel cannot dry out. But acid rain often has a pH of 4 and can have a pH as low as 2. Washing galvanized steel with potable water that has a neutral pH is essential to preventing acid rain damage.
Exposure to pH over 12 can occur when galvanized steel is exposed to bleach or disinfectant. If a galvanized steel surface is disinfected, it must be washed with neutral, potable water as soon as possible after the disinfectant has had a chance to do its work.
Another long-term consideration in maintaining the finish on galvanized steel is insulating it from contact with dissimilar metals. Copper and brass encourage electrochemical reactions that deplete the zinc coating on galvanized steel.
Do not clean or degrease galvanized steel with abrasive cleansers. The process of wetting and drying in normal weather builds up a protective patina of zinc over galvanized steel that protects it from the elements. Constant abrasive cleaning destroys the patina, so it has to be built up over and over again, bringing time to first maintenance unnaturally early in the life of the steel.
When galvanized steel is placed in service in coastal or industrial locations, it needs to be washed with water on a regular basis to remove potentially corrosive salts and chemicals. And galvanized steel should never be stored in a damp, poorly ventilated warehouse.
Removing Build-Up on Galvanized Steel
With responsible maintenance programs, galvanized steel will accumulate minimal build-up once it is in service. But it is not uncommon for contractors to be unaware of or insensitive to the need to store newly galvanized steel in pristine conditions so that stains and marks occur before the steel is placed in service.
Fortunately, there are a number of options for removing stains and marks on galvanized steel. But there are some general rules for successful removal of build-up on galvanized steel.
- Always opt for the most conservative approach to cleaning steel. If relatively gentle methods don’t work, then move up to more vigorous cleaning methods.
- Avoid mechanical and abrasive cleansing methods whenever possible. Mechanical methods of cleaning zinc surfaces result in aesthetic issues. When scrubbing is required, use a hard plastic brush rather than a steel brush to minimize the visual contrast between areas needing cleaning and those that don’t.
- Test any cleaning method in an inconspicuous area first before applying it to the entire surface of the steel.
General contaminants like dirt are easily removed with laundry soap. The more stubborn areas may need a pressure wash after application of soap. Soaps used to wash cars and trucks are designed to protect metals and often get good results on galvanized steel.
Mild stains from ponding of water and beverage (particularly wine and soft drink) stains usually respond to application of household ammonia cleaners. Dilute the ammonia cleaner to avoid excessively high pH that can damage zinc, and rinse off the ammonia cleaner with potable water after it removes the stain.
Brown stains from runoff from adjacent untreated steel can be removed with the same oxalic acid cleaners used to clean pots and pans. Oxalic acid also helps to remove cement and mortar.
Graffiti should be removed with a combination of non-alkaline paint thinners and wooden or plastic — never metal — paint thinners. Rinsing after paint removal is important so potentially corrosive chemicals are not left on the galvanized surface.
Looking for a place to get started with stain and build-up removal?
The American Galvanizers Association (AGA) has tested some widely available commercial products for removing organic contamination with good results. These products include:
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- Comet®
- Bleach
- Goof Off®
- Simple Green®
- The Must for Rust®
- Stainless Steel Cleaner
The AGA recommends these products for removing stains:
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- CLR
- Lime juice
- Naval jelly rust dissolver
- Picklex 10G
- White Vinegar
Always test vinegar, ammonia cleaners, and muriatic acid in inconspicuous locations before applying over large surfaces.
