About 8 or 9 years ago I carefully treated all knots with Langlow Knotting stuff and undercoated and finished with Dulux Gloss white. Now the knots are showing through, particularly where exposed to sunlight. Should I sand right back to the knots and re-apply the knotting solution, or simply key the gloss, apply solution and then gloss?
Sand it down and paint over and beyond the knots with Zinsser BIN, it is a high adhesion shellac based primer which will cure your problem. Read and follow instructions as detailed on container.
Got so frustrated with my pine stairs I coated the lot in aluminium primer. 2 undercoats and then satin... Zinsser bin will be your best bet x2 over knots unless there are loads.. Maybe aluminium primer in the sunny spots? Stir it well as the aluminium becomes solid at the bottom and its a gray colour hense it's a pain to get white but nothing with ever get through
The new Smith and Rodger blockade is better than Zinserr bin in my opinion, goes on easier and has less smell and its cheaper, and all jobs I have used it on have been spot on with no problems.
I get mine from Topdec Decorating Supplies https://www.topdecbrush.co.uk/product-page/blockade-sealer-primer-2-5l
Zinsser BIN at Screwfix, 2.5l @£33.99 inc VAT, topdecbrush, Blockade sealer primer £34.80 does that price inc VAT?