wrote in message
oups.com...

My significant-other paints professionally and she's seen bleed-through
of *something* through the walls a number of times. Cleaning the walls
thoroughly before painting is necessary but isn't always sufficient.
If memory serves, she does use an oil-based primer in such cases----and
THAT isn't always sufficient. Though it usually works if enough coats
are applied.

Oil based primer is not necessarily the solution. By "primer", I assume you
mean a stain blocker. You have to know what you're trying to block
(assuming it can't just be washed off first.) As a general rule, use oil
based primers for water based stains, and water based primers for oil based
stains (for fairly obvious reasons - oil and water don't mix and therefore
can't bleed through.)