Q: Can you help us with an annoying problem? We had a leaky roof that left water spots on the bedroom ceiling. We fixed the roof and repainted the ceiling, but the stains keep reappearing. And yes, we primed the ceiling first.
A: You can’t use just any old primer; you need to apply something that’s specifically labelled as a stain blocker or stain killer. Because you’re dealing with a water-based stain, don’t bother with a water-based primer. Use an alkyd- or shellac-based primer, as these won’t reactivate the stain.
-Roy Berendsohn and David Agrell