exterior wood stain block

Hello, help needed please. I sanded right back to wood, primed, undercoated & painted with exterior paint a previously varnished wood porch. There are yellow stains bleeding through & running down the porch now. Do I need to stain block & repeat top coat, is Ronseal stain block ok for exterior use. Thank you, from a novice!
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jsdoor


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On 10/06/2014 7:28 AM, jsdoor wrote:

Is it knots bleeding or general overall problem? For knots and other sap from pine and similar woods, re work those areas back to base and use a shellac-based primer or a coat of shellac.
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jsdoor;3292759 Wrote: > Hello, help needed please. I sanded right back to wood, primed, > undercoated & painted with exterior paint a previously varnished wood > porch. There are yellow stains bleeding through & running down the porch > now. Do I need to stain block & repeat top coat, is Ronseal stain block > ok for exterior use. Thank you, from a novice!
No, not necessarily.
If you used a latex paint, those yellow stains could very well be something called "Surfactant Exhudation", which is a fancy technical word for saying "the soaps in the paint are bleeding out of it".
Take a damp sponge and see if you can clean those yellow stains off. If so, it's soap you're cleaning up.
Surfactant Exhudation is caused by high humidity or rain occuring shortly after painting. The surfactants (pronounced "soaps") in latex paint will be attracted to the moisture on one side of the paint film and will bleed through the paint film to it's surface, causing yellowish or brownish discolouration of the paint.
The other possibility is that the wood you painted was cedar, redwood or Southern Yellow Pine. All of these woods have a lot of tannin in them, which gives them their distinctive colours. Tannins are soluble in water, and so if you primed with a latex primer, the tannins would have bled through the primer and you SHOULD have seen that bleed through on the primer before you painted. If you then painted with a latex paint, the tannins in the primer would have bled through the latex paint too.
If you can tell us what kind of primer you used (whether latex or alkyd), how long you waited after priming before painting, what kind of paint you used, and if there were any notable changes in the weather shortly after painting, then we can possibly help more.
But, it sounds like surfactant exhudation to me, and cleaning it off with water would confirm that. You should start to notice more and more bubbles in your cleaning water as you remove more and more soap from the painted wood decking. Surfactant exhudation causes no damage to the paint, and neither does removing the soap after the paint has dried.
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nestork


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nestork;3292794 Wrote: > No, not necessarily.

> something called "Surfactant Exhudation", which is a fancy technical > word for saying "the soaps in the paint are bleeding out of it".

> so, it's soap you're cleaning up.

> shortly after painting. The surfactants (pronounced "soaps") in latex > paint will be attracted to the moisture on one side of the paint film > and will bleed through the paint film to it's surface, causing yellowish > or brownish discolouration of the paint.

> Southern Yellow Pine. All of these woods have a lot of tannin in them, > which gives them their distinctive colours. Tannins are soluble in > water, and so if you primed with a latex primer, the tannins would have > bled through the primer and you SHOULD have seen that bleed through on > the primer before you painted. If you then painted with a latex paint, > the tannins in the primer would have bled through the latex paint too. >

> alkyd), how long you waited after priming before painting, what kind of > paint you used, and if there were any notable changes in the weather > shortly after painting, then we can possibly help more.

> with water would confirm that. You should start to notice more and more > bubbles in your cleaning water as you remove more and more soap from the > painted wood decking. Surfactant exhudation causes no damage to the > paint, and neither does removing the soap after the paint has dried.
Thank you, I appreciate the time you have taken to help me. In answer to your questions: I have wiped the porch & although some staining was removed, the majority is left behind. The stain is patchy in appearance. The window frames are almost fully stained, the door stains washed off.
I used Rustins quick dry primer & undercoat "does both jobs" apparently with two coats. I then used Ronseal weatherproof exterior wood paint. Both note that brushes should be cleaned with water/detergent.
I have not used the top coat on the door yet as all seemed to be going badly wrong - which remains primed/undercoated only & ? may explain the different results.
When sanded the wood appeared different on door & window frames.
I waited a good 24 hrs before using top coat paint on window frames. In the morning when I went to use the top coat the stain was present but minimal & intensified after top coat.
The weather was fine, chilly & frosty overnight before topcoat used.
Hope this helps you - once again your advice has been excellent & hugely appreciated, thank you.
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jsdoor


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On 10/7/2014 6:29 AM, jsdoor wrote:

I suspect that low temp is an issue....what was daytime temp when you painted? Most coatings that I recall using have a low-temp limit of about 50F, as does Rustin. Coating in full sunlight can also be a problem, letting a film dry before solvents can escape from under the film. I would wait for consistent warm, dry weather and then try correcting. Acryllic paints can bleed out resin, even long after application. You need to figure out whether there is liquid coming out of the paint, which your description suggests, or whether pigment under the paint coat has dissolved out of previous coat or wood and combined with the paint. A good photo would help, and you can email Rustin for help. Here is their data sheet, which says "a minimum of two coats is required".
http://www.rustins.eu/ProdData/Quick%20Drying%20Primer%20&%20Undercoat.pdf
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