Plaster marks

Hi, My apartment that I have lived in since it was built (now 18 months) has developed marks on the painted plaster board. I only noticed these marks after about 15 months from when the apartment was first built. The only way to describe them is that someone has put there fingers in grease and created a speckled effect all over the wall. It has only happened on the walls that are on outer walls but these are not Westerly facing (apparently this wall is normally the coldest and attracts moisture). I did have a picture frame on one of these walls and after taking it off the back of it was covered in mildue.
The apartment is under NHBC 10yr (not that it counts much) and I’ve had the builders out but they have been unable to explain it apart from lack of ventilation \ drying. They recommended treating it with a stain block type substance and decorating but I'd rather sort out what the problem is, any ideas?
James
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     snipped-for-privacy@earthling.net (james Mc) writes:

It does sound like ventilation/condensation. What to you do to ventilate? Do you keep window trikle vents open? Do you open windows? Do you use an extracter fan in bath/shower room and extracter hood over hob when cooking?
However, I am surprised that a new place would get condensation over the last 3 months. I wonder if there's no insulation in the outside walls, and/or if you have some abnormal source of water vapour in the building. Is there a damp smell? Might be worth spending a couple of quid on a humidity guage (a cheap greenhouse one would do) so you get some idea what the humidity is inside the apartment.
--
Andrew Gabriel

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My guess is a bridged cavity or failed damp proof course. If the effect stops at a certain height, then it may be the DPC, if not, it is more likely a bridged cavity. This could be lack of care not to drop mortar on the ties, or could be an inappropriate insulation material (such as open cell foam) that allows water to pass through. If the entire wall is coated, then the insulation is more likely, as the bridged wall ties would cause a very patchy effect.
Christian.
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The effect does not stop at a certain height, although it is quite bad at one particular spot at the top of the wall. Previously I mentioned it was speckled in this instance it is constant mark for aprox 5cm wide and 500cm long.
I live on a 1st floor apartment so I'll check with my downstairs neighbour if they have suffered a similar effect. The only I can mention is that my neighbour across the landing suffered a similar effect as well.
James
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