We see this in about one out of every ten or fifteen cast-iron and steel bathtubs. For whatever reason, the bathtub manufacturers neglected to check to make sure the tub drains properly. Usually there is a slight low spot about an inch to three inches in front of the drain. Typically it lets about 1/8 of an inch of standing water, but we’ve seen it as deep as a 1/4 inch. This standing water eats away at the finish over time, leaving an ugly ring. Often times, these fixtures are refinished for this very same reason, and the problem is almost never corrected. Because of this, the tub will need to be refinished again fairly soon. The picture below shows a previously refinished bathtub with a low spot that was not fixed. As a result the coating in this area has completely come off. We check for this problem, but most refinishers don’t and likely don’t care. The process of fixing this sort of problem is time consuming and usually isn’t profitable, which is why most refinishers would rather just ignore it.
