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I am painting some wooden internal window sills and skirting boards, and a yellow-brown stain is showing through the paint. From the answers to What are the brown stains showing through my white paint? and Primed wood and painted with white paint but looks yellow. Why and how to fix?, it looks like it is probably tannin leaching out of the wood and through the paint. I'd like to know how best to fix the problem, ideally without having to sand back to the bare wood and start again.

I'm not sure what type of wood it is, but it was a reddish colour, and previously covered with a dark red-coloured varnish. The varnish has been scraped off, then sanded down and primed with white 'Valspar Wood Primer & Undercoat'. The stain was quickly visible through the primer, so a day or so later, a second layer of primer was applied before painting with white 'Dulux Quick Dry Satinwood for Wood and Metal'. While this initially looked OK, the stain is now starting to show through again.

The answers to the questions linked above talked about using primers to stop staining in the first place, but didn't really discuss how to make good stains that were coming through. After all the painting I've done so far, I'm not keen to sand it back to bare wood and start again with a different primer. Is there anything I can apply on top of the satinwood paint to stop the tannin coming out before a final coat? Recommendations for products I can get in the UK would be welcome.

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    I have answered several similar questions here with the advise to use a Shellac based primer. Use the search function to find them. You do not have to sand back to wood, just prime with the shellac and paint. – Alaska Man Aug 28 at 17:30
  • @alaska man make that an answer. Kilzs and zinsser Are the 2 brands I use most commonly, I really haven’t seen many others but any shellac based primer should stop it. That was the only thing that stopped the cigarette tar from coming through even after TSP cleaning it was bleeding through at my grandparents house, after a coat of shellac it quit bleeding through. – Ed Beal Aug 28 at 21:10
  • I was going to recommend a shellac-based primer as well. Always get good results with that stuff. – Greg Nickoloff Aug 28 at 21:31
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I use a shellac based primer for things such as this. It has better hiding ability then just paint or regular primer.

Give it at least two coats or more and see if it hides the problem and then you can apply the final paint. It goes on very thin and appears to not be hiding the stain but don’t let that fool you it is creating a impenetrable barrier over the stain.

For added insurance you could give it a coat of a good bonding primer and then do your final painting.

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  • I went with two coats of Zinsser B-I-N shellac-based primer, which went on thin as you said, but nearly hid the stain on its own. It's now looking good with a single layer of topcoat, and nothing's coming through so far. Hopefully that will do the trick. – JRI Sep 1 at 19:16
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You may have wondered with all these low odor paints available why would anyone use a smelly paint? One answer is to find a paint that will not absorb the stain.

You don't need to sand back to wood, just scuff sand to dull the sheen so that a fresh coat of different paint will stick. however if there is a texture you want to disguise you can sand deeper.

Use a paint with a contrasting chemistry as undercoat, EG: use an oil-based paint with an organic solvent, or a shellac based sealer with an alcohol solvent if your main coat has a water solvent.

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    You wan have wondered”. Lucy, you have some splaining to do. 😉 – Alaska Man Aug 29 at 5:55
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The reason for this is likely you’re not using a stain blocking sealer / primer.

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  • How does this answer the question about how to make sure the stain does not bleed through? This is a comment and not an answer. Please take the tour so you know how to participate here and provide good, detailed and informed answers. diy.stackexchange.com/tour – Alaska Man Aug 29 at 5:57

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