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Strange patches on interior walls


 
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darokika

from United Kingdom

Joined: 25 Feb 2011
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Fri Feb 25, 2011 9:03 pm Reply with quote

Hi,

I have reskimmed walls in the kitchen, living room, hallway and stairs of my grandfathers house which I am currently doing up for rental purposes. The walls in the kitchen, hallway and stairs are fine and have been painted with a good result. However one wall in the living room has a mysterious 'damp' looking patch at the base of wall just above the skirtboard.

The wall in question is an interior wall and was left for 5 weeks prior to painting with matt emulsion. The new plaster was also sealed prior to painting. There are some smaller 'damp' looking patches on some of the other walls, one being right at the top of a chimney breast. The 'damp' looking patches are not actually damp to touch and the paint has dried well however these strange patches have developed and are clearly noticeable. I have tried to repaint the patches but as soon as the paint drys the patches return. All the other walls I have done in the house have turned out well without the same problems, can anyone shed any light on this and what is best to do??

Paul
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sixeighth

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PostPosted: Fri Feb 25, 2011 9:55 pm Reply with quote

Paul - what did you seal the walls with?
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misterhelpful

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PostPosted: Fri Feb 25, 2011 10:35 pm Reply with quote

Sounds like it could be some sort of moisture issue.

Even though you say you waited 5 weeks, was the plaster completely dry when you painted?

A patch just above skirting level could certainly be damp, even on internal solid walls. Also, have the other patches appeared or worsened during wet weather? If so, then it could be due to water penetration so check exterior walls for damage. Likewise the chimney, and the flashing.

If the chimney is unused and blocked up, does it have adequate air vents as any moisture within has to escape somehow?

If all is well, then a stain-blocking damp seal paint will cover minor patches before re-painting but will not cure damp.
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darokika

from United Kingdom

Joined: 25 Feb 2011
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Fri Feb 25, 2011 11:47 pm Reply with quote

Hi,

I used a mix of water / PVA to seal the new plaster - I have used this with all the other walls in the house, they are fine with no problems.

The house is a terraced house and there were no signs of dampness prior to plastering, plus it has just undergone a survey for mortgage purposes and no damp issues were noted and this was tested for by their machine.

The patch on the chimney breast is the size of a cereal bowl, again there were no signs of damp on that wall. Plus the chimney has been well used and indeed a new gas fire / surround has just been installed.

It is a total mystery and is really frustrating.

The only thing I did differently to any other walls is that I painted the walls initially using silk emulsion but ran out after I put one coat on the walls. Without realising, the new paint I put on after was matt emulsion. Surely this wouldn't caused this issue??

Paul
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sixeighth

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PostPosted: Sat Feb 26, 2011 7:37 am Reply with quote

I don't know what's causing it but wonder if it's related to the pva mixture which is not recommended as a sealer for unpainted plaster. If there were spots that weren't 100% dry then maybe the pva is preventing it drying out at the surface (whilst allowing it to feel dry)?

If the pva mixture wasn't well mixed maybe it went on thicker in those spots?

The only other thing I can think of is contamination of some sort in the skim mix (assuming there were no sign of these spots before the re-skim).

I know you're looking for answers not questions so hopefully someone will have something more definite.
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darokika

from United Kingdom

Joined: 25 Feb 2011
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Sat Feb 26, 2011 9:51 am Reply with quote

Thanks for your comments.....

I'm going to sand off the problem areas and check the plaster behind the paint...maybe that will give me some idea

I'll let you know....

If anyone else can add more light to this issue please let me know
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JohnD

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PostPosted: Sat Feb 26, 2011 12:39 pm Reply with quote

photos would be nice http://www.diynot.com/forums/viewtopic.php?t=129539

is the chimney ventilated top and bottom?

did the plaster have dark or shiny patches before you painted it?

PVA is unsuitable to paint over.
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darokika

from United Kingdom

Joined: 25 Feb 2011
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Sat Feb 26, 2011 6:45 pm Reply with quote

I have now sanded the area in question. The plaster is totally dry however is slightly dark in colour.

The chimney is ventilated both top and bottom. The patch on the breast is not as obvious and is small in comparison to the other interior wall and not so dark.

I have heard alot of fors and against in regards to using PVA/Water mixture as a sealer so its hard to know what advice is best - I'm not a trades person so its all fairly new to me, however I am quite a competent DIYer.

Any advice is greatly appreicated.

Now that I have taken the patch back to bare plaster and confirmed it to be dry, would it be best to reseal it and paint it again???

I will take some pics tomorrow and post if it will help.
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misterhelpful

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PostPosted: Sat Feb 26, 2011 7:18 pm Reply with quote

I have occasionally used PVA on new plaster (Decorator 20 years) and have never had any trouble. It MUST be mixed thoroughly and to the correct ratio otherwise it will dry on the surface rather than being soaked in. I do prefer diluted emulsion though.

I think problems occur when a brand not suitable for sealing plaster is used - the tin/bottle will say if it is - or if the plaster has been over- polished.

Dark patches that feel dry to the touch can still be from moisture or even stains from underlying brickwork/old water stains (Have there been any previous leaks in these areas?) bleeding through.

Pics should help diagnosis.


Last edited by misterhelpful on Sun Feb 27, 2011 12:29 am, edited 1 time in total
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TheDec

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PostPosted: Sat Feb 26, 2011 8:18 pm Reply with quote

Paul if it is your intention to apply a paint system Never ever apply pva as a sealer coat, if I were you I would remove all traces of paint from the effected areas and wash off with a cloth and warm water.

When dry apply a coat of oil based undercoat before you continue with any further paint system.

Dec
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