wrote in message
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I replaced some wood on a camping trailer last year. I never got it
painted. It's been under a tree all year. Now this new wood has a
green slime or green (something) on it. [What is it?].

Do I need to sand this all off the wood, or can I just scrub it with
bleach, or can I paint right over it? I plan to use an oil based
paint.


It's probably penetrated the wood. Replace the wood and paint it immediately
this time. You could try cleaning it bleach, but you'll probably have a
tough time knowing if the wood is still in good shape beneath the visible
surface.