Just as doors and drawers become tight with high humidity and loose in dry air, the keys of your piano may stick down when struck in times of high humidity. When the environment surrounding your piano is dry the keys may seem to rattle when played.
As you play your piano, you will notice how responsive the keys are to your touch. The way the keys cause the hammers to strike the piano strings is part of thousands of interconnected wooden parts called the piano action. With high moisture levels in the piano action, the action is sluggish, and the keys seem non-responsive to your touch.
Bridge and Soundboard Damage
The soundboard is the single largest piece of wood in your piano. It actually vibrates to amplify the sound produced by the strings. The bridges of your piano are joined to the soundboard and support the strings.
As the soundboard absorbs moisture from the air surrounding the piano, it swells, producing an upward bulge. Through the bridge, this puts additional tension on the strings. Now, the pitch is too high in the lower mid-range and treble section.
When the soundboard shrinks and flattens, the tension of strings over the bridge becomes inadequate. The pitch of the mid-range and treble section is now flat.
Over time, constant changes in humidity levels, with the corresponding shrinking and swelling of the soundboard, will damage the integrity of the soundboard. You will see this damage in the form of a crack in the soundboard.
Pinblock Damage
The strings of your piano are held tight by the pins in the pinblock. As the pinblock absorbs moisture in periods of high humidity, it swells, crushing the wood fibers against the pin.
In dry periods, the wood shrinks away from the pin, loosening it and causing the string to sag. When this cycle is reapted time after time, the wood fiber surrounding the pin are destroyed and lose their resilience.
In this picture, this pinblock (without pins) was removed from a piano during restoration. With continuous swelling and shrinking, the wood could no longer provide the snug fit required to hold pins in place.
String Damage
The strings of your piano are responsible for producing the musical sounds. With exposure to high humidity levels over long periods, strings become rusted and corroded.
At the junction where rusted strings wrap around rusted pins, rusted corrosion forms a hardened bond between the two. Then, during a tuning, when your piano technician turns the pins to stretch the strings, the inflexible rusted string snap at this joint.
Copyright © 2006 The Piano Co.