In message .com,
" writes
I need to waterproof a wooden sash window in the bathroom, to protect
it from the shower.

It's already had a coat of oil paint, but from past experience that
won't be enough in the long term.

I was thinking of applying 3 coats of Rustins Yacht Varnish. This does
have the disadvantage of gradually discolouring over time, but would I
imagine otherwise do the trick.

Does anyone have any comments on my plan, or suggestions for
alternatives (I'm not interested in changing the window, or resiting
the shower)?

does the window protrude into the shower, or is recessed into the wall?

In our old house we had a small louvered window (used to be the toilet)
that was recessed into the wall (flush with the outside) I fitted a
piece of frosted glass in the recess - set back so as to leave ledge. I
made a frame of aluminium angle and then set the glass in this using
silicone sealant. The was enough ventilation from the louvres to prevent
any condensation/mould etc. in the gap between the windows.
--
Chris French