[gtojohn]

I'm not sure how environmentally friendly it is but Kilz or Zinsser primer does the job. I did a stubborn mildew spot over our shower and its been mildew free for 15 years. Other uses besides the obvious, on fire damaged houses, really water damaged from the firehose, here they Kilz primer the framing that isn't replaced. This also makes it easy to identify houses that had fires. If I recollect correctly there is a similar additive that can be mixed into any paint.