Streaks in the plaster after painting

Hi,

The following situation: We have gypsum plaster, and on the ring beams and lintels the plaster dried very slowly. That’s understandable, concrete doesn’t absorb the water; with Ytong the wall dried really quickly. In the end, there were still some damp spots left. Mainly on the lintels at the doors. When you ran your finger over them, no change was visible, but after a few minutes the spot suddenly looked dry.

Now we have painted directly on the plaster, and the spots where you ran your finger over stand out from the rest. There are clearly visible streaks. We have already painted the lintel three times, without improvement.

The surface is completely smooth – so there are no scratch marks, especially since we wiped over it with the finger without pressure.

What could be the reason? Is there still more moisture inside than in the rest?

Pictures say more than 1000 words...
How long could the plaster dry?
What kind of paint did you use?
What did you prime the plaster with?
How was the plaster treated afterwards?

Drying: almost 3 months

Color: Renovo Crystal White

Primer: none, painted 3 times with color. The other walls only needed 1-2 coats - also without primer

Plaster: no post-treatment, was smooth like a baby's bottom from the beginning

Something is sucking differently there, and you skipped [TiefGrund]. Try sanding block, 240 grit, light sanding, don’t make scratches, then dust off, apply paint again. I give no guarantee, but it might work.

Well, a guess: Usually, a sinter layer forms on the plaster, which you may have wiped away with your finger, causing the substrate here to absorb while it does not do so next to it. For a clean finish, plaster is actually sanded and primed. Sand the lintel with fine paper, then apply a primer once and paint again afterwards, that should solve the problem.

Oki doke, thanks, we'll give it a try.