A.Robin Raymer of Plasterzone.com, an author, educator, and veteran plastering contractor, responds: How you treat the water stain depends on the type of coating on the ceiling. Unlike smooth-coat plaster, which must be finished with primer and paint, sand-finish plaster can be either painted or left its natural color. Or it can be tinted before application, a trend that seems to be increasingly popular.

If your sand-finished ceiling has not been painted, you can try to bleach the stain out. Mix one part water to one part bleach in a mist bottle and lightly spray the stained area until it's wet but not dripping. (Be sure to protect everything underneath, and wear skin and eye protection.) I usually spray in the morning and then let it sit till the evening, or even till the next day. Keep spraying the stain until it's no longer visible; I've had to repeat this process six or seven times before the stain finally disappeared. I've found that using an old toothbrush to rub the area lightly helps quite a bit, but be careful not to rub too hard.

If bleaching doesn't work, your next option is painting the entire ceiling. How successful this approach is depends on what caused the stain and how stubborn it is. Painting the whole ceiling is not popular with homeowners, because the primer and paint fill in a lot of the ceiling's texture; if there's a swirl pattern on the ceiling, much of it will be lost when the paint coats it.

Yet another option is to take a "flat" primer and thin it down, then put it in a mist bottle and spray the area very lightly so that there is not a noticeable buildup. This helps knock the stained area out so that it's not quite so visible. Some contractors use Kilz (Masterchem Industries, 866/774-6371, www.kilz.com), but this product leaves a slight sheen that tends to show up on flat sand-finish ceilings.