Do You Live near a Beach or have a Pool?
Salt & iron particles in the air float around & land on the metal, they then will build up quickly. You may notice that they will start to go milky, this layer will need to be removed as soon as possible, before it cant be restored and the damage is done.
Swimming pools & around Hot Tubs have chlorine in them that also reacts over time.
It’s called this because the stainless starts to go brown, it’s from the water modules that land on the metal that rusts not the stainless material itself, as shown in our example here. To prevent this it must under go regular maintenance.
Even Tree Sap causes Damage
With external handrails they can accumulate sap from trees & bushes, this will give them brownish type spots & sometimes can feel gritty or sticky.