Is the black spot on the surface of the water-based paint mildew? - Ask the water-based paint expert

2019-06-11

Is the black spot on the surface of the water-based paint mildew? - Ask the water-based paint expert


Problem:

The wooden doors of our company's surface veneer have no black spots before they are painted. After spraying the water-based paint (primer + top coat), black spots appear on the veneer during the natural drying process. I wonder if the water-based paint is mildewed? If the oil-based colorant is used to seal the bottom, will the water-based primer finish avoid such problems?

Response:
According to your description and photo analysis, the phenomenon you are experiencing is not the mildew of the waterborne wood, but the chemical substrate of the wood substrate you use. This is because there is no black spot in the wood. This is the case when the wood is unevenly colored, and when it is dry, it will be swollen with water or the solution will swell. Most wood is chemically treated. Black spots do not occur when the chemical treatment is good. However, in some cases, such as excessive hydrogen peroxide accumulation or unidentified stains, there will be black spots on your picture.
We recommend that you try to wash the surface of the wood with water or sprinkle, and then dry the paint. We feel that after solving the problem that the substrate is not clean, the problems you encounter can be solved. For wooden doors that have been painted, only remove the paint and clean it.
Sealing the bottom with an oily colorant and applying a waterborne primer finish may not solve your problem. This still depends on the substrate. If the substrate is not clean, black spots may occur, but the solvent has little effect on the fiber, and the black spots are not so obvious.
I hope our answer will help you. If you have more specific requirements, you can contact us directly. For more information on waterborne coatings, you can also visit sinograce chemical's waterborne coatings knowledge base and recipes in our waterborne formula library. Or ask us directly through our question water-based paint expert column.

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