How Moisture and Time Affect Woodwork

I have a sixty-something cabinetmaker friend across town who has taught me quite a bit about wood. A few years ago he said “I'm not making any more white cabinets!”

In spite of his very best efforts, the wood joints would begin to show after as little as six months: just a hairline crack at the joint. But apparently, for some customers, that was a cause for wailing and gnashing of teeth.

Well, he hasn't stopped making white cabinets, because people love white. But, for the sake of making you into a smart homeowner, I thought I would delve somewhat into the subject of wood and moisture.

Assuming that your home has air conditioning (cooling) in the summer, then the highest moisture periods in your home will be spring and fall.

But isn't the moisture in the air greatest in summer? Yes, the outside air has more energy (temperature) in the summer and is therefore capable of supporting a greater load of water. But when that air begins to circulate through your cooling system, it passes a “cold point” (the refrigerant coils) to which the moisture tends to stick. This is why you have a constant drip from your AC unit.

So, the AC has both a cooling and drying effect, meaning that your house's greatest humidity period is the warmest period when the AC isn't running, meaning Spring and Fall.

This fluctuation of moisture from summer/winter (dry) to spring/fall (wet) acts like a kind of pounding and pulling on your woodwork. In the spring, a joint takes a mighty pound, and in the fall it takes a mighty pull. Though a well-made joint can withstand this pressure, the paint/lacquer finish often cannot. Hence the cracks in my friend's cabinets. This does apply to your trim work, too: crown, base, etc.
What can be done?

Short answer: Grin and bear it.

In his years of experience (and mine), no amount of finish or end-grain sealing (end grains are known to be more receptive to wicking) is able to prevent moisture from getting into a life-size piece of woodwork. Water is a fiesty little devil, but maybe that's why we can't live without it.
So if you can't live without white and you want real wood doors, just accept these hairline joint seams as part of life on planet earth. You may get lucky and not have any, but — statistically speaking — a normal sized white woodwork project will have a handful of them after five years.