All items are quenched in a passivation solution to assist in the prevention of light white oxidisation. Quench colouring will vary subject to thickness of the steel, and will fade as the hot-dip galvanized coating forms its natural patina while the item is in service. Very thick sections may display deep yellow or green shades, which are unavoidable and not an acceptable cause of rejection.
Passivation
For a short period after galvanizing the outer layer of the hot-dip galvanized coating is susceptible to the formation of zinc oxides. To minimise effects of light white oxidisation, items are passed through a bath of passivation solution. This process can impart a yellowish film to the galvanized coating. On most items the film will be barely visible; however, on items of heavier thickness it may appear much darker. This does not detract from the quality or performance of the coating and will generally remain visible for about six weeks when, following natural weathering, the patina will form.
Light white oxidisation / White Rust / Wet Storage Stain
Light white oxidisation may form as a thin film of chalky powder. It occurs on freshly galvanized zinc coatings in times of high humidity or after a period of rain. Provided the items are well ventilated and permit moisture to drain or evaporate quickly, light white oxidisation rarely progresses past this superficial stage. If required, it can be easily removed by applying a low acidic product such as vinegar or CLR Clear with a nylon brush. Otherwise it will generally wash off in service and with normal weathering, the patina layer will develop. In this form, it is not detrimental to the hot-dip galvanized coating, and remedial treatment is not required.
Wet storage stain is a more severe form of light white oxidation, caused by prolonged storage of items packed closely together in a humid, damp or poorly ventilated environment. Product such as lintels, guardrails, and other items that are tightly nested, are at risk of incurring wet storage stain if stored externally in their configured bundles. Air must be permitted to circulate freely around all zinc surfaces when stored. Wet storage stain will not occur on items where moisture is unhindered and can evaporate naturally.
If items are bundled in close configuration for an extended period, fresh water or moisture such as rain, dew and condensation can react with the pure zinc outer layer of the hot-dip galvanized coating. Unable to escape, this moisture will form zinc oxide and zinc hydroxide.
In the majority of cases, this does not reduce the expected life of the zinc coating. However, if moisture remains trapped between zinc surfaces, medium to heavy build-up can cause extreme damage to the coating and may result in the items having to be stripped and re-galvanized.
Light wet storage stain will disappear once bundles are opened, items separated, and allowed to dry. The wet storage stain will convert to the dull grey zinc patina as it reacts with carbon dioxide in the air. Items that have formed their protective patina layer generally will not be susceptible to wet storage stain. Medium or heavy wet storage stain is very dark or black in colour. At this stage, a significant amount of the zinc coating has been consumed and the patina will be prevented from forming.
The storage stain deposits should be brushed from the area and the coating reinstated by applying approved zinc-enriched epoxy paint to a thickness of about 100 microns.
Whilst passivation of items after galvanizing will minimise the occurrence of wet storage stain, the best precaution is to avoid stacking products in poorly ventilated, damp conditions. Wet storage stain is found most often on tightly stacked and bundled items, such as galvanized sheets, plates, angles, bars, hollow sections and pipe.
To ensure wet storage stain does not occur, we strongly recommend items be removed as soon as possible after despatch to allow adequate airflow across all surfaces. Break all bundles of items apart to allow moisture to evaporate and prevent the occurrence of bulky white deposits or wet storage stain.
Staining and wet storage deposits are outside of our control and we are unable to accept any responsibility for such occurrences.