My next project is to paint a large room in our house. The ceiling is
covered with a type of fiberboard tile with a finish that is made to
look like wood grain. The finish is an off white color, so it looks
like the bark on a white birch tree, sort of. The tiles interlock,
toungue-and-groove, and are of different lengths and widths, so that
it looks like the ceiling is covered with planks.

In one area, the tiles are water stained from when a radiator leaked
on the floor above. I don't want to tear down and replace the whole
ceiling, so I'd like to paint the ceiling and was thinking of some
sort of sealer, like Bullseye White Shellac. Anyone have a better
idea?