Knots bleeding through - BIN?

24 Dec 2004
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United Kingdom
Hi, we had a new staircase fitted about 4 years ago, painted professionally after.

Now there are multiple brown areas showing through the white painted woodwork.

I've read Zinsser BIN works well, do I need to sand back to the bare wood where the knots are or can i simply do a couple of coats over the knots after light sanding down? There's no resin to see, just brown circles where the knots are.

Help appreciated.
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Sand over and spot prime should be enough. BIN can "Flash" that is show through the topcoat if it is smoother or less absorbent than the surrounding paint. Tends to be more common on emulsion paints but if it happens another top coat should hide it.
I had a similar issue after using professional decorators once.

Solution is to spot sand the knots back to bare wood. Use Colron Knotting solution, rather than BIN, just on the knot. Repaint as necessary. No flashing.
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I have used both knotting and BIN on balance my experiance is the BIN worked best it is a very similar formulation, shellac and meths as a solvent. BIN has a colour pigment added to improve covering. Knotting is the original solution to the problem.

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