This is a very expensive acrylic paint, the bucket was not properly closed, and left 1 year in the basement.

Zolpan acrylic paint with mold inside

Now there is mold inside the bucket ; The strong smell of acrylic has also disappeared.

It doesn't need to be perfect quality, since I just wanted to finish the painting of the technical room of my house. But well.. brown color spots would certainly look awful on the white walls. (On top of that I could bring mold inside the house..)

Maybe I could filter the paint into another clean bucket, and and try to stir it anyway ? Or this is too dangerous, there was a chemical reaction and my paint is dead ?

  • 2
    Potentially related question should you use this paint: diy.stackexchange.com/q/40573/36011 Apr 10, 2020 at 10:28
  • @statueuphemism At least it gives me the correct "key word" which is sour paint
    – JB.
    Apr 10, 2020 at 10:33
  • 1
    That's not mold, it's rust. From the metal handle. Apr 10, 2020 at 14:24
  • In the words of Clint Eastwood, do you feel lucky? If you do paint with it and the finish fails (flakes off/ doesn't dry properly/ ...) are you that far behind? Or is your time/effort valuable enough that you should just buy new paint? Apr 10, 2020 at 16:56

4 Answers 4


Try using a spatula and clean off the moldy area, it might just be some rust, without disturbing the rest of the paint so you don't mix the mold/rust in. Once it's cleaned up, stir the paint and determine if the texture seems right and then paint a scrap piece of wood and see what it looks like. The fact that you don't have the acrylic smell means the chemicals that keep the paint liquid and spreadable have weakened and that's not a good sign. You've waited a year, try a test spot and see what it looks like...

  • 3
    +1. Would suggest floating a circle of cling film on paint before removal of mold/rust, to limit debris falling in while cleanung.
    – bishop
    Apr 10, 2020 at 16:44
  • Indeed the smell is not a good sign, I have read about sour paint and don't want to provoke a disaster. Will try your method anyway.
    – JB.
    Apr 10, 2020 at 20:40
  • @JB.WithMonica. If it was cheap paint I wouldn't even suggest it... just buy a gallon...
    – JACK
    Apr 10, 2020 at 21:03
  • The remaining liquid was a sort of muddy white water. Does no longer look like my acrylic paint. Will not use it, especially if this is sour paint.
    – JB.
    Apr 11, 2020 at 8:29
  • Definitely the smart way to go. Good luck with the project and stay safe out there.
    – JACK
    Apr 11, 2020 at 12:20

Throw it away. If it is mold there is more in there than you can see. You do not want to risk bringing that mold into your home or workspace.


Use it, the pigment in paint is far more powerful than the mold, it won’t cause brown spots discoloration, spore growth etc, All this is fear mongering. The worst thing you’ll face is that if the mold might smell at first but will dissipate as it drys, don’t waste it. Even heard of some people who pour a tsp of vanilla extract into paint for those sensitive to paint smell — vanilla extract is dark brown alcohol — also doesn’t change the paint color. There is a lot of hearsay and speculation in matters like these, just use it it will be fine, if you Plan to store the left over add a tbsp per gal. of borax powder and get a clean well sealing can appropriate to the size of the remainder

  • 1
    Considering that this counters "conventional wisdom", some evidence supporting your point would add some weight to it. Otherwise, it's just "some user on the internet said...".
    – FreeMan
    Jun 2, 2022 at 15:10

From the dry material on the outside it looks like you have a 5 gallon bucket of primer with about 1 gallon left.

You can see the paint is a bit broken by looking at the watery outside edges. It may be usable still though but it is not going to have the same properties as it was supposed to.

On the rust - not mold - well rust is a pretty damn good coloring agent. It is already in the paint. Probably the best thing to do is find the cleanest side, wipe that side of the inside down really good with paper towel to remove rust and dump this into another bucket that can be stirred.

You will have some rust remnants in your paint and it will not mix exactly even. If the room you are painting is going to be of a lighter color or white there is a very very good chance that the rust coloring will bleed through. (I don't think this will happen - but if there is enough rust bleeding through you might have to go over the whole area in something like Killz to really cover it - this would turn a quick paint job into a mini-disaster)

Verdict: Unless I was doing something like an interior of a shed I would just throw it away. I hate throwing stuff away but I also hate having to redo something and pay for materials to redo something (brushes/rollers/pans). We are talking about ~$10 worth of paint and you will be using ~$10 in materials and your time is worth?

  • This is a 16l bucket, weights about 7kg, so 7l left. Seen on the web as 28€/l ... still expensive :-)
    – JB.
    Apr 10, 2020 at 20:30
  • Plus this is COVID time, kinda hard to go to the drugstore buy some paint :-)
    – JB.
    Apr 10, 2020 at 20:37
  • @JB.WithMonica. - ok why ask the question if you only wanted one answer? You can have primer delivered just like anything else. How do you go to the store to get more paint, brushes and so on to cover up this paint?
    – DMoore
    Apr 10, 2020 at 20:55

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