Flexner on Finishing: Furniture Deterioration
by Bob Flexner
Everyone who buys, sells, works on or collects old furniture, or who has some in their house, has to be concerned with deterioration. It’s staring them in the face every time they look at the furniture.
Totally stopping the deterioration isn’t possible, but it can be slowed. To do this you need to understand its causes.
Though indoor furniture isn’t exposed to rain or direct sunlight (the elements that destroy exterior wood), indoor wood still warps, splits and separates one board from another. The primary cause is wood movement – the shrinking and swelling of wood brought on by changes in relative humidity.
In most parts of the country, relative humidity inside a house is usually fairly high in spring and summer and low in winter when the house is closed up and the heat is on. Heating lowers relative humidity because it increases the amount of moisture air can hold. The absolute amount remains the same, but the relative amount declines.
The most obvious example of the problem occurs in wood windows and doors. In the spring and summer they jam because the wood has swollen to reach equilibrium with the moisture in the air. In the winter they open and close easily. Those with an exterior exposure let in cold air.
Because wood shrinks and swells far more across the grain than along the grain, joint failure and veneer separation are almost inevitable when the glue ages and becomes brittle. Stresses caused by leaning back in chairs, for example, speed the failure.
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