Dark marks on walls after decorating

Adam RB · 19 Feb 2018

Hi,

I have just finished applying two coats of Matt emulsion to my kitchen walls, on what I thought looked like an excellent flat service. However there seems to be some strange marks on the walls, quite noticeable at certain angles. Any ideas what could be causing it? Or how to rectify?

Thanks for your help.

JohnD · 19 Feb 2018

kitchen walls are usually very dirty.

Did you clean them before painting?

Is there any sign of damp, such as a previous water leak from the room above?

They look a bit like trace marks where a plasterboard wall on wooden studs shows the pattern of studs due to temperature difference causing condensation or dust shadows. Tap the wall. Do the marks correspond to the position of studs? This is more likely on a drylined cold external wall.

Adam RB · 19 Feb 2018

I gave them a quick wipe down but not a thorough clean to be honest. The patches are almost raised. Was thinking of completely sanding down the marks and repainting?

JohnD · 19 Feb 2018

I've edited in some more thoughts.

Adam RB · 19 Feb 2018

Thanks John. No the marks don’t appear to relate to the studs and are on a few of the walls to be honest.

Would sanding down or using a primer be the best solution?

JohnD · 19 Feb 2018

try scrubbing first. If the paint comes off, it might have been a greasy wall. If not, give it a couple of coats more paint and it may go (you can use matt white vinyl, which is cheapest and good for obliterating marks). Stir it very well to mix in the solids which hide marks.

It might possibly have been damp related, causing condensation on the walls and interfering with the paint drying, so air the room well before and after painting, and heat it first if cold. Misty windows indicate excess humidity.

You can get stain blocking paints, but they are rather expensive, especially if you need to treat the whole room.

Robbie uk · 20 Feb 2018

Walls need a thorough sanding first. Apply the paint with a decent roller and don't over roll it out too much or you will get dry edges.

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Dark marks on walls after decorating

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