Treating Water Stains

This window had leak issues ( rain , sprinklers ) some years back, which have been solved by replacing the window, and doing other repairs.  In the photo, I’ve applied my light blue wallpaper primer to the top half of the wall but not yet the bottom portion, so that’s why the color difference

Even though the leak has been stopped, vestiges of it are still appearing.  Water that entered the wall left vertical streaks on the drywall .  All these years later, after the paint and texture have been removed , the stains remain.

Water stains , along with some others, such as blood , rust , ink , marker , grease , oil, cosmetics , and the like, will bleed through joint compound , primer , paint , and wallpaper , creating new stains on the surface .  It may take a couple of months , but they will make an appearance . In this photo, I’ve already applied my blue primer. It only took a half an hour for these stains to work their way through.

This is the top right corner of the window , where the bracket for the mini-blinds is attached to the wall.  Note the stains on the underside of the window . 

To prevent these stains from working their way through the new coating / paint / wallpaper , it’s imperative to thoroughly cover them with a stain blocker .  And – trust me – water-based products won’t work, despite what the label claims.  You need an oil-based product like this KILZ Original , or a shellac-based like BIN by Zinsser .  Both are prone to splatter , so be sure to cover your floor and baseboards with dropcloths .  KILZ has strong fumes and can make you high , so ventilate or wear a respirator mask .  It’s a hassle cleaning the liquid out of the brush , so I use a cheap-ish disposable “ chip brush ” from Home Depot or Sherwin-Williams .  The products usually dry pretty quickly.
Note that wallpaper paste won’t stick to most oil-based primers , and shellac is too glossy for good adhesion , so I’m going to go over the stain blocker with my usual Roman Pro 977 Ultra Prime wallpaper primer , which sticks to just about everything , and creates a good, matt finish surface for the wallpaper to cling to.