Re: Painting Tongue and Groove Knotty Pine
You need to use a stain blocking primer such as Kilz (original, not Kilz2 which is worthless ) or a pigmented shellac. You don't just put one coat on, you put as many as it takes to seal whatever the stain is and keep if from bleeding through.
I would recommend first applying a single full coat across the entire surface, then I'd go back and spot prime the knots and problems spots with one or two coats, then follow that with another full coat across the entire surface. This method will help to prevent "hot spots", or "shiners" where there is a build up of primer in one area more than another. Once you are certain that the bleed through is stopped, then go ahead and apply two coats of your top color.
Application method will depend on the surface. Spraying is easiest, but it doesn't leave behind a very thick layer with which to block stains with. Rollers work well to get the material onto the wall and spread around, followed with a brush to lay off the dimples and work the primer and paint into all the nooks and crannies.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!