In 1994 when our house was built, the cabinet subcontractor was displeased that new EPA regulations were making him use water-based finishes, due as I recall to their attempt to minimize toxic vapor exposure both for industry employees during application and customers as the finish cured over time. I would guess that is why the specific era of coaches here is having the issue; they have water-soluble finishes that, when exposed to higher moisture content air, absorb some of it on the wood surface. Older, more volatile and vaporous oil-based formulations would conceivably be more moisture repellant.
My subcontractor warned that our cabinets would likely be less resistant to discoloration than any built previously, and sure enough they haven't held up all that well, especially whitening along the door edges or floor area where the wood is exposed more to wet mops or hands, and seams where the wood grain changes. Fortunately, the cabinets are maple (we had grown tired of the commonly used oak cabinetry during our house-hunting) and don't show it quite as badly as a darker wood probably would. The cabinetmaker had no confidence in the finish he was forced to use, and said we'd probably somewhere along the line have to use extra-fine steel wool to knock down the bad spots, and apply clear Varathane.
I've never been confident enough in my refinishing abilities to tackle the job in the house, and Lee brings the issue up regularly, so one of these days I'll have to get out the steel wool, close my eyes, and start in. After 21 years the discoloration has become so extensive that it detracts from the value of the house, and I should just bite the financial bullet and have a cabinet professional redo them all with a modern finish.
I have to think that the industry fought back by coming up with more durable, moisture-resistant formulations subsequent to that mid to late 90's period, and which still met EPA guidelines for volatility and toxicity. The clear finish on the cherry in our '06 Beaver hasn't shown any noticeable deterioration, certainly not like what happened within only a few years in our house. I'm sure the wood experts at any of our resources in Bend have been there, done that more than anyone, and could proffer advice to those with coaches from that era.
Yes, relative humidity can be higher in the northwest and southeast, but I'd expect it to be more damaging in places like Florida than Washington, for example. The warmer moist air I'd think would be more aggressive at penetrating the more open pores of warmer wood substrate, and the chemistry of a softer warm surface finish that's designed from the get-go to dissolve in water. The humid air dissolution, however, isn't controlled and is incomplete, resulting in microsolids that appear as a haze.
Joel
