Porcelain sinks are very common and susceptible to cracking. Unfortunately, there is little you can do about the problem. However, learning the different reasons a porcelain sink cracks can help you prevent the problem from reoccurring. If your new or old porcelain sink is cracked and you don't know why, one of several issues could be to blame.
One of the more common reasons a sink cracks is due to a very rapid or extreme change in temperature, like when a pot of boiling water is poured into your sink. Since porcelain is usually layered on metal and metal is a conductor of heat, the sink loses heat fast and becomes very cold, even when your bathroom or kitchen isn't cold. When hot water contacts the cold porcelain, it creates temperature stress that cracks the surface of the sink. To prevent this from occurring again, never pour hot liquids into a porcelain sink that has not been used for several hours.
A less interesting, but no-less realistic, reason for a cracked sink is a dropped item or contact by a falling item. Anything heavy and solid will crack a porcelain sink fairly easily, especially if dropped from a substantial height like the top of the medicine cabinet. A glass jar of cotton balls, a can of shaving cream or even a heavy metal shaving razor that drops into the sink from cabinets above will cause a crack in the sink. Avoid placing heavy items on shelves over the sink; instead place them beside the sink or in the sink cabinet drawers.
Accidents do happen, and oftentimes the results of the accident are ignored or unnoticed until later. Any sudden forceful contact with your sink, even from behind the sink wall, will cause a crack in the porcelain. If you moved a new appliance into the bathroom and it struck the sink, or were hammering away at the wall right behind the sink, the shock could crack the sink. Even leaning on the sink for a prolonged time will stress the porcelain and could lead to a crack.
Cracks Form Over Time
In some cases, the crack does not form all once. Instead, it forms over time and is nearly impossible to tell what caused the crack. If you just noticed the crack and nothing serious occurred within the past month or two, this might be the reason. Cracks will grow over time because the object is now compromised and therefore weaker. The crack might begin as just a hairline fracture, impossible to notice at just a glance; however, smaller additional shocks will slowly enlarge the crack until you can see it easily.