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!

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

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.

--

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.

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.

Thank you for taking the time to assist me. General problem I am afraid, no knots were apparent in wood when sanded.
best wishes.

On 10/7/2014 6:29 AM, jsdoor wrote:
nestork;3292794 Wrote:
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.

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.




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...0Undercoat.pdf