My c. 1850 farmhouse was a double-plank construction, and the interior walls are mostly the original hemlock planks. Early this morning I walked into my guest room and noticed white spots all over the dark wood walls. Then I looked up and saw white streaks on the wood beams and ceiling. It appears to be mildew, or some other kind of white mold. It looks horrible!

The ceiling of that room is the attic floor. We've had so much rain this summer, and my dehumidifier has been running in the living room most of the time. I discovered two roof leaks last week, so I suppose water has been coming into the attic. I will be getting quotes in the next few days. The cost of a new roof is not a happy thought, but I don't know what to do about the guest-room mildew.

I read that white vinegar works best on porous wood, and I suppose I can use something on a pole to apply it to the beams and ceiling. Would it help if I bought another dehumidifier for that room? Do you have any other suggestions?

Thanks!