In theory, the color coated steel coil clean needs to be done once every six months. And in the coastal with many salt frog and industrial dust heavier places, cleaning should be more frequent.
Generally the clean water is ok, but for the obstinate stains which is difficult to clean can use weak water-soluble detergent or household ammonia cleaning.
Whatever the case, scrub unobtrusive small pieces to test before large area cleaning. When looking up to the related data, CAMELSTEEL found a pretty sample method:
Take a spoonful of detergent of less than 0.5% phosphate content into 5 gallons of hot water, or taking a cup of household ammonia into 5 gallons of room temperature water. Do not mix ammonia or detergent with any bleach. When using any of above detergent, saturated in soft cloth, sponge, soft brush or low pressure nozzle from top to bottom to clean the surface of the steel sheet, to avoid wiping streaks and producing bright spots.
It is advisable not to use decontamination powder or industrial detergents because it will damage the paint. If there’s fungi or mildew, the above method can not be removed, it is recommended to use bleach-containing detergent. The steel surface after washing need to eliminate the detergent vestigital completely.