The problem: He said he had rust in pin points on his sink. He told me that his contractor used an unidentified white powder to remove the spots but they came back. He also said he has a number of scratches in the sink. I asked him what kind of finish he had and he replied a sating finish.
The diagnosis and fix: small pin points of rust can come from a number of sources. At first I suspected the cause was “metal dust” left over from the manufacturing and fabrication process. During the manufacturing of the sink and the fabrication of the countertop there are a lot of processes that involve grinding, sawing and polishing. These processes produce metal dust from saw blades and grinders. This dust can settle on the sink and be unnoticed until the sink is used and the metal dust is exposed to water. The metal dust then rusts and shows up as pin points. If this is the cause a good cleaning by Barkeepers Friend or similar cleanser normal removes the spots. Spots from metal dust do not return.
Another cause of rust spots is the water supply. If water with a high iron content is left in the sink to dry it can leave behind residue. Usually these spots are larger than just pin points. Rust spots from this source can also be cleaned with a stainless steel cleanser. They will return unless the iron is removed from the water supply. It helps to dry the sink after every use. Rust from water supply will tend to reappear in a different place in the sink each time.
Rust can also come from metal objects left in a wet sink. It is not the sink that is rusting but the metal object; can, screwdriver, screws, etc. This is surface rust and can usually be easily removed. It will only reappear if the source of the rust was not removed.
Stainless steel sinks should not rust. Stainless steel is defined as 11% chromium and will not rust (it can stain, however.) Stainless steel sinks at typically made with 18% chromium. There can be iron impurities in the stainless steel that rust. These impurities will continue to rust and the sink needs to be replace.
I have also seen some of the older three piece sinks rust where the bowl meets the top plate where they are welded together. It is the weld not the stainless steel that is rusting. These sinks need to be replaced as well.
Unfortunately if you need to replace a sink you usually need to replace it with the same brand sink as most manufacturers have a unique cut out in the top for the sink. It is better to make sure you have a high quality sink in your top.
In the next article we will discuss scratches in stainless steel sinks.