A roof leak leaves you with an ugly stain on the ceiling even after the leak is repaired. But you don’t want your family and friends to see it tomorrow at Thanksgiving Dinner, so you need a quick fix. You can’t just paint over the spot with ordinary paint because the stain will bleed through. The solution is a stain blocking primer. Look for one in a spray can…. Preferably with a vertical spray nozzle for ceiling application. Several paint manufacturers have products designed for just this situation, so their flat white finish matches most white ceilings. First cover the area beneath the stain with a drop cloth and then begin lightly spraying the primer to cover the stain….when it disappears, feather the primer out around it, so the repair is less visible.