I have black spots and streaks on some cedar siding that was replaced last summer. The new siding (right side of photo) was primed and painted with a stain (2 coats).

black spots and streaks -- new siding on the right side (taken from: https://www.flickr.com/gp/bobkh/5t9wc7 )

What can I do to fix this issue ?


  • 1
    Welcome to WSE. Links to photos are discouraged since the links can be lost. Could you please place the photo into your question by choosing to edit it and adding the image in the editor?
    – Ashlar
    Jan 10, 2018 at 16:37

1 Answer 1


To me it looks like mildew, even if only at the beginning.

If true, you should give a good sanding to the wood and then you should use some anti-mustiness product and then reapply the primer and the paint.

Eventually you can, before sanding to the wood, try to give a light sanding just to check if it is just superficial in which case you can probably just use some good anti mustiness product.

  • Are you sure you mean “mustiness”?
    – Steven
    Jan 11, 2018 at 4:00
  • In my language is "muffa", in English mold ? mildew ?
    – Gianluca
    Jan 11, 2018 at 10:07
  • that makes more sense
    – Steven
    Jan 11, 2018 at 12:27
  • I think it's mostly superficial. I will apply some 30 second cleaner when it stops raining and see how that goes and post back with results.
    – Bob
    Jan 12, 2018 at 15:15
  • The 30 second cleaner worked really well. Still boggled why it occurred on the newly installed and painted cedar, rather than all the siding.
    – Bob
    Jan 13, 2018 at 19:43

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