A local piano tech well-known to me recently went to fix a problem that a Yamaha upright owner had with sticking keys. This piano is not a grey import — it was bought from Yamaha Singapore. The cause of the problem was obvious — the keys had swelled because of the heavy rain we’ve been having everyday for the past couple of weeks. (For those who don’t live in Singapore, during a torrential tropical downpour the raindrops are the size of cows, not cats nor dogs. And it comes down in bathtubs, not buckets.) The piano was situated in the non-airconditioned living room.
The usual advice that all piano dealers and techs give is that for uprights in Singapore, an always-on heater bar in the case is all that is needed to keep the action in good shape. Indeed, even I have said that before, but now I will correct myself. We’ve all forgotten that the front length of the keys are outside the case, and therefore not protected from high RH.
Fortunately, the swelling is reversible. You just have to lower the RH around the piano to between 50% to 60%, until the keys have dried out sufficiently to un-stick. Obviously the best long-term solution is to aircondition or dehumidfy the room to keep the RH between 40% to 60%, but that’s not practical for some owners.