wrote

| I'm planning to paint a 10 year old textured living room ceiling that
| has some dark stains showing under the rafters. I have been advised to
| cover the stains with a product such as Kilz before I paint but my
| questions is, why can't I paint the entire ceiling with Kilz and leave
| it at that? Do I need to cover the Kilz with a separate coat of paint?
|

Kilz will have an uneven sheen, though if you use
the water-base type it might be OK.

I would question whether you even need it. Are you
sure you actually have stains? If you have gray shadows
at rafter locations that's probably due to poor or no
insulation. That area gets colder, moisture condenses,
moisture picks up dust/soot. You see a gray shadow.
You may see darker spots where drywall screws are
located. That can just be painted over. It's not a stain.