Symptoms
- A key goes down normally but rises slowly or only partway
- Several keys feel heavier or stiffer than the rest, often in the middle of the keyboard
- The problem gets worse in summer or after rainy weeks and improves in dry weather
- A key rubs or catches against the key next to it or against the wooden strip in front of the keys
Likely causes
Swollen key bushings
Each key pivots on metal pins lined with small felt bushings. In humid air the wood and felt swell and grip the pins too tightly, so the key returns slowly.
Key rubbing on the key slip or fallboard
The wooden strip in front of the keys (the key slip) or the fallboard can warp or shift and rub against the fronts of the keys.
Debris under or between keys
Coins, pencils, paper clips, crumbs and children's toys are common culprits. Anything wedged between keys or under the key frame can drag a key.
Spilled liquid or sugary residue
A drink spilled onto the keys leaves residue that glues keys together and can also swell the wood beneath them.
Warped key or worn action parts
Less often, the key itself has warped or a part in the action is binding. This needs a technician to diagnose.
What you can safely check yourself
- 1Measure the room with an inexpensive hygrometer. Aim for 40-50% relative humidity; above about 60% sticky keys are common.
- 2Look between the sticky key and its neighbours with a flashlight and gently remove anything visible with a thin card, not a metal tool.
- 3Press the key at the front and at the back near the fallboard. If it only sticks at the front, it may be rubbing on the key slip.
- 4Note exactly which keys stick and whether it changes with the weather. This saves the technician time.
- 5Run a dehumidifier or the air-conditioner's dry mode for a few days and see whether the keys loosen up.
What not to do
- Do not spray WD-40, silicone spray or any oil into the keyboard. It soaks into the felt, attracts dust and makes the problem worse.
- Do not pry keys up with a knife or screwdriver; you can chip the keytops or crack the key.
- Do not remove the key slip or the action on a grand piano unless you know how; parts can easily be damaged or misaligned.
- Do not dry the piano with a heater or hair dryer aimed at it.
Quick fixes vs. call a pro
You can usually handle it
- Lowering room humidity with a dehumidifier or AC
- Removing a visible coin or pencil between keys
- Wiping a light spill off the keytops right away
- Tracking which keys stick and when
Call a technician
- Keys still sluggish after the room is dry
- Many keys sticking at once
- A liquid spill that ran between the keys
- Keys rubbing on the key slip or on each other
What a technician will do
A technician eases the swollen bushings with a special key-easing tool, adjusts or shims the key slip, and removes debris from under the keys. On an upright this usually takes 15-45 minutes and is often done during a regular tuning visit. Spill damage or warped keys take longer and may require removing the action.
A piano holds about 18–20 tonnes of string tension. If a fix means opening the action, turning tuning pins or working near the strings, leave it to a technician.
In Israel
Sticky keys are especially common in coastal cities such as Tel Aviv, Haifa, Netanya and Ashdod, where summer humidity often exceeds 70%. Pianos in closed apartments without air-conditioning during summer holidays are frequent cases.