We moved into a victorian semi and have had some extensive plastering carried out. On 2 walls (both external) the plastering was carried out very neatly, but when it dried, not only did we have large dark masses appearing, but the surface went powdery an white 'crystalish' in swirls. It will not accept paint or any kind or sealer/retarder. Does anyone have any suggestions - as hacking it off around our new kitchen will be a challenge i'm not relishing
Sounds like efflorescence. This is caused by the salts in the plaster coming to the surface in the drying out process of the new plaster.
Don't wash it off 'cos all you will do is get a recurrence. Instead just brush it off then you can paint normally.
If, however, it's not just due to the plaster drying out and there is a damp problem behind then it will just keep coming back until the damp problem is solved. The data you have given so far, thouygh leads me to believe it's just normal drying out.
No you are right - you can't paint over it - you have to brush it all off first.
What sealer / retarder have you been using on it? Your answer will determine next step advice.
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