strange substance appearing on newly painted walls

dezki

i recently had my outside shed refurbished to create a home gym. the walls were plastered and i recently finished the paint job. On one of the walls, a strange dark green coloured substance appeared on one part of the wall, i've painted over it, washed it off but it keeps coming back, what the hell could it be?

safesecure.ie

Hi Dezki,

Had a similar issue, couldnt figure out what it was but was told to paint over it with gloss paint first, then with what whatever paint I was painting the rest of the room.

Worked a treat - although I prob really should have found out what was causing it and treated it!

Joey the lips

safesecure.ie wrote: »

Hi Dezki,

Had a similar issue, couldnt figure out what it was but was told to paint over it with gloss paint first, then with what whatever paint I was painting the rest of the room.

Worked a treat - although I prob really should have found out what was causing it and treated it!

Thats does not sound like a good idea. If you paint gloss onto a surface without an undercoat it peels. If you paint over gloss without using an undercoat is peels...

Blizzard

My sister (living in the U.S.) had a similar problem in her basement and it was mould. She would wash it off the walls and then a few days later it would reappear. I think it also has to do with ventilation / dampness. Do you have the shed ventilated? You might want to look into that if you see it reappear.