Paint is patchy on newly plastered walls

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kevincassidy

New Member
My new build house was plastered back in May this year and I have left the windows open to let it dry out naturally. I have got the heat on in the last few weeks. I have started to paint the walls with undercoat and for some reason the walls are coming out patchy. If I put on a second coat it does not improve. I have 2inch dry-lining on all outside walls but this is happening on both outside and inside walls regardless. The ceilings are taking the paint fine.

Has anyone every came across this before, or have any suggestions on why its happening?
I've added some photos.
Any help would be good.
Cheers
Kevin
Paint is patchy on newly plastered walls
Paint is patchy on newly plastered walls
Paint is patchy on newly plastered walls
Paint is patchy on newly plastered walls
 
I take it you mean trade emulsion for the undercoat? To me it looks like a shite sponge finish that is basically dust that you've gone over. Done right it's bang on but done wrong you're just troweling up snot.
 
looks like paint mapping. seen it on skimmed walls over S&C. from cold spots i think the painted said
 
copy and pasted from:
https://www.askaboutmoney.com/showthread.php?t=114739

''This problem ( known as Mapping or Murphys Defect ) is due to variable porosity of the plaster surface, generally caused by overtrowelling of the plaster. The areas where the paint is slow to dry have low porosity and often the surrounding areas where the paint is absorbed readily show a build up giving the "map" appearance.This mapping problem only occurs on solid block plastered walls and not on plasterboard surfaces such as ceilings or partition walls.The problem cannot be seen in the raw plaster state, it only becomes evident when paint is applied.*Generally, when the first or second coat of emulsion has fully dried application of additional coats are OK. It may be necessary to sand any raised areas to even up the surface. As a last resort you can apply a coat of Dulux Sealapore which seals the surface and evens out the porosity


From years ago.
 
Donzo said:
copy and pasted from:
https://www.askaboutmoney.com/showthread.php?t=114739

''This problem ( known as Mapping or Murphys Defect ) is due to variable porosity of the plaster surface, generally caused by overtrowelling of the plaster. The areas where the paint is slow to dry have low porosity and often the surrounding areas where the paint is absorbed readily show a build up giving the "map" appearance.This mapping problem only occurs on solid block plastered walls and not on plasterboard surfaces such as ceilings or partition walls.The problem cannot be seen in the raw plaster state, it only becomes evident when paint is applied.*Generally, when the first or second coat of emulsion has fully dried application of additional coats are OK. It may be necessary to sand any raised areas to even up the surface. As a last resort you can apply a coat of Dulux Sealapore which seals the surface and evens out the porosity


From years ago.
Click to expand...
Cheers Donzo, i'm getting the problem on both block walls and drylinned walls, but the ceilings are fine. Ill try the second coat tomorrow to see if it gets better.
 
If I'm painting fresh plaster and I see it drying funny I just let the first coat completely dry then go back over it again and it should be fine. If you tried applying more coats while the first was still wet it does make it look worse
 
kevincassidy said:
Cheers Donzo, i'm getting the problem on both block walls and drylinned walls, but the ceilings are fine. Ill try the second coat tomorrow to see if it gets better.
Click to expand...
Stuart is correct above.
I have also seen it on other surfaces.

If it persists,i have seen in extreme cases a decorator painting it with oil based undercoat then emulsion.
They are a lot of variables that can cause this.and its a common problem .
Good luck it should come good.
 
Last edited:
Did you water down the paint for the first coat? The first coat should be well watered down the second a small bit and no need to add any water to the last coat
 
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