- Our spots are fungus, caused mostly by exposure to a humid environment
- The jarn vitrol colors the wood but doesn't protect it from fungus, algae, etc.
- The splotches are cosmetic and do not impact the structure of the wood at all
- His own house has a few areas much like mine
- There's a specific product I can use to remove the fungus if I wish
- Stefan provided me the name and phone number of his fungus advisor and I've asked Rutger to give him a call on my behalf
So the bottom line is that we don't have to do anything at all, the problem is just cosmetic. If we want a different look (other than splotchy), we'll need to paint. We might need to treat the house before painting; that's still an open question. But at least we have a good line to get a final answer on procedures and products.
UPDATE 1: Rutger spoke to one expert today who said it's very hard to tell if we killed the fungus with our previous treatment in September, and in any case, it could well regrow by next spring anyways. We can leave it and see how the house looks next year with no harm, but if we want to paint, we should scrub it again before painting. The good news it's only the one exposure of the house, not the whole thing.