Our sheet flooring has a
dirty yellow stain that has appeared
under a throw rug. What is it, and
can it be removed?
There are two possibilities, depending on whether your floor is vinyl or linoleum.
1) Small rubber mats and throw rugs with non-skid backings have certain additives in the rubber, called antioxidants, which help the rubber stay supple and flexible for many years and many washings. Unfortunately, these antioxidants also can react with linoleum and vinyl flooring, producing a characteristic staining or discoloration.
Unfortunately, this staining is not removable, so the best defense is a good offense... don't use any rubber-backed rugs on your vinyl floor unless it is clearly marked as non-staining to vinyl floors!
By the way, this problem is not limited to rugs. Rubber feet on stools and rubber wheels on microwave carts can also cause this problem. Metals, hard plastic and wood generally do not cause this sort of staining.
2) There is a second type of discoloration that is peculiar to linoleum, called "blooming". Linoleum's base ingredient, linseed oil, oxidizes when exposed to light. This reaction brings out the "true color" of the floor, according to Armstrong Flooring. However, if the floor is covered with a rug or refrigerator, the area may appear yellowish. Fortunately, the true color will reappear if the area is exposed to light again for a length of time.