Stainless Steel is inherently corrosion resistant materials that do not need additional surface protection to enhance their appearance and durability. Some routine maintenance and cleaning is needed to keep stainless steel surfaces in good condition so that the aesthetic appearance and corrosion resistance are not compromised. These guidelines are to give building owners, developers and facility managers advice on efficient, cost effective cleaning that will allow them to take advantage of the corrosion resistant properties of stainless steel.
The Self-Repair Mechanism of Stainless Steel
It is important to understand why stainless steel is so corrosion resistant. The alloying elements in stainless steel form a thin, transparent “passive layer” on the surface. Although this protective passive layer is only a few atoms thick, it instantaneously reforms in the presence of oxygen from air or water, so even if the material is scratched or damaged the passive layer continues protecting the surface from corrosion. This explains why stainless steel does not require any coating or other corrosion protection to remain bright and shiny even after decades of use.
Initial Cleaning
The first cleaning is generally done before the building is handed over to the owner. If the stainless steel parts have been protected adequately then simple “maintenance cleaning” at the hand-over stage will probably be sufficient. Specialist cleaning is needed to clean mortar and cement splashes as well iron particles which can dramatically reduce the product’s lifespan if not attended to properly.
Maintenance Cleaning
On external applications, such as facades, rainfall can normally be expected to wash off accumulations of dirt and other deposits efficiently, depending on the amount of exposure of the elevation. Special attention should be given to sheltered areas during routine cleaning to ensure that accumulations of airborne contaminants are removed. On interior applications, finger marks can be an issue. There is a wide range of finishes available for stainless steels, many of which are particularly suitable for use in heavily exposed (high traffic) public areas. Selecting finishes that are less sensitive to fingerprint marking in the design process will reduce the effort and costs of cleaning during the service life of the finished building.
Cleansers
To remove fingerprints and other marks from architectural finishes, soapy water or a mild detergent are usually safe and successful. Proprietary spray cleaners are available, which combine ease of cleaning with a light film that produces an even and smooth lustre. Mirror-polished stainless steel can be cleaned with glass cleaners. These products should be selected chloride-free. For more stubborn stains, mild household cream cleaners should be effective. This should also be suitable for cleaning off watermarks and light discolouration. After cleaning, remove the residues with (preferably de-ionised) water (available in supermarkets, e.g. for steam ironing or car batteries) and dry to avoid streaking and water marks. Severe oil and grease marks can be removed with alcohol based products, including mentholated spirit and isopropyl alcohol or other solvents such as acetone. Care is needed with solvents to avoid spreading the staining on the stainless steels, which can then be difficult to fully remove. It is advisable to apply clean solvent several times with a clean, non scratching cloth, until all traces of the partially dissolved oil / grease are removed. Paint and graffiti can be treated with proprietary alkaline or solvent-based paint strippers. The use of hard scrapers or knives should be avoided as the underlying stainless steel surface may become scratched. Heavily neglected surfaces can be treated with metal polishes, such as those for cleaning chromium-plated items (e.g. automotive trim). Furthermore, polishes used for re-finishing car paint can be considered. Care must be taken as highly polished surfaces may become scratched with these cleaners. Alternatively, use a proprietary stainless steel cleaner containing phosphoric acid to remove contamination, rinse with de-ionised water and dry. It is advisable that the entire surface of the component is treated so that a patchy appearance is avoided. Cleaners that should NOT be used on stainless steel include:
- chloride-containing cleansers, especially those containing hydrochloric acid
- hypochlorite bleaches should not be used on stainless steel; if applied accidentally or spilt on stainless steel surfaces, should be rinsed off immediately with liberal amounts of fresh water
- silver-cleaners must not be used on stainless steel
Cleaning Utensils
A damp cloth or chamois leather will usually be suitable for removing normal soiling, fingerprints, etc. For more stubborn dirt, nylon pads such those known as “Scotch-Brite” pads are usually satisfactory. Non-stainless steel based scouring pads, cleaning wool or wire brushes must not be used on stainless steel. Apart from scratching the surface, these pads can leave carbon steel deposits on the stainless surface, which can subsequently develop into rust spots, if the surface becomes wet. Soft nylon brushes can be used for cleaning stainless steel with patterned finishes. Non-stainless steel wire brushes must not be used. On “grained” directional finishes, such as EN 10088-3 types G, J and K the direction of cleaning strokes should be along the grain and not across it. Where water has been used for cleaning or rinsing, wiping the surface dry to prevent watermarks, especially in hard water areas may be advisable. The use of de-ionised water will prevent the formation of hard water staining.
Cleaning Intervals
The cleaning of stainless steel items for building interiors is really no different to other materials. Cleaning should be done before there is a visible build up of soiling or finger-marking, so that the effort and cost of cleaning is minimised along with the risk of marking or altering the appearance of the surfaces. On building exterior applications, stainless steel may be exposed to a wider range of potentially more aggressive environments as a result of contact with:
- marine atmospheres
- environments laden with industrial pollutants
- salt spray from road de-icing salt
- atmospheric dirt and traffic film
It is a good practice to clean the stainless steel at the same frequency as the building’s windows (glazing). Depending on the severity of soiling and deposit build up, routine cleaning frequencies of 6-12 months for light soiling and 1-3 months for heavy soiling or environments such as those listed above is advisable. A stainless steel cleaner containing phosphoric acid will remove this form of contamination.