If you don't want to rub down (AIUI knotting has to be applied to the bare
wood), you could try Polycell's "Stain Stop". But ring them to check if it
will work, cos the can doesn't mention knots.
I have had to tackle this problem in several replacement timber
windowframes of recent years.
Traditionally the answer is "Japan Gold Size" which is probably still
otainable. It is of course neither japanese nor golden. I treated
numerous knots indoors on skirting boards etc. by using a blowlamp and
scraping off all the paint I could. Then I applied good white
undercoat, twice, then gloss. Since this effort NO RECURRENCE of the
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