Stains coming through stainblock. Does it mean it's still damp ?

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Hi

I had some brownish stains come through ceiling in the back bedroom a year or 2 ago, edwardian terrace, about 30cm away from the edge of a chimney breast. This happened during times of torrential downpour with high winds when a lot of houses leaked that do not usually. At least I thought so

The ceiling is lath and plaster

I am having that room decorated and zinsser coverstain has not blocked the stain. It was used twice. Some stains worked but 2 are still showing, albeit paler than before

The decorator said it could be the stain is still damp. It hasn't rained for a while though

Any thoughts ??

Many thanks
 
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Hope you can see it; very faint. Don't think its mould. Looks like water stain
One of the stains is almost in the middle of the picture, to the right of centre
They used Zinsser cover stain twice
 

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Zinsser coverstain is oil based. If applied correctly water stains should not be able to penetrate it.

Although it shouldn't be necessary, I would apply a coat or two of Zinsser BIN over it.
 
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It looks like moisture penetrates through the wall. Have you any suspicions on the other side of the wall? Any cracks or pipes going through that wall?

New paint isn't a permanent solution. The right way doing this is to stop the water sources. After that, wait for a few days wall to dry. In the end, fresh paint should be applied.
 
Hi
Its a ceiling. Not much rain recently so should have dried out.
 
Even if the ceiling were still damp, water stains should not penetrate through stain blockers.

In most cases, if the water was still an issue the stain blocker would blister or crack as it is pushed away from the plaster. I cannot see any evidence of that.

If the surface was wet when the guys painted it, the stain blocker would have gummed up as they painted it.

I have no idea why it didn't work the first time around and am not in a position to doubt that they did anything wrong.

My advice would still be to apply one or two coats of BIN. At this time of the year, it can be applied and a second coat applied after about 30 mins, and then a further 50 min before applying the emulsion.

I use household ammonia to clean the brushes. It is an alkali and breaks the BIN rather than simply diluting it. I decant some in to a jar (with a lid), dip the brush for a few mins and rinse it under a cold tap. Zinsser recommend meths but I suspect that is for legal reasons. Ammonia stinks, but it way more effective.
 
Great tip about cleaning brush etc. I will be trying some more stain block after hols
 
Great tip about cleaning brush etc. I will be trying some more stain block after hols

Before discovering the ammonia tip, I used to use throw away brushes, unfortunately they are horrible to work with. I now happily use £15 brushes with BIN because I now know that the brush will be perfectly clean after.

Other than BIN, you could purchase Blockaide by Smith and Rogers, it is about 10% cheaper. Both are pigmented shellac paints. The cheapest option, if you are only trying to cover that area, would be to use a shellac based knotting solution. It is "clear" but cheaper and available in smaller bottles. Alternatively, use oil based undercoat, but you will need to wait longer before you can paint over it.
 
I used my own pot of Zinseer coverstain and hey presto the stains are blocked. I wonder what they did use, or just 3rd time lucky...
 
I used my own pot of Zinseer coverstain and hey presto the stains are blocked. I wonder what they did use, or just 3rd time lucky...

I don't want to malign the guys but I am glad that you managed to sort it out. Thanks for letting us know.
 

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