As my piano service matures, I find myself thinking more and more that many pianos need new hammers rather than just reshaping. The older felt is simply too hard and dense to work with anymore, it’s impossible to create a warm, welcoming sound in the music. There’s a few reasons for this:
When you can’t achieve the sound you want, playing the piano becomes a self defeating endeavor. I don’t want to over prescribe this maintenance so I went searching for validation and below is an answer I found on a public message board validating my position.
Like everything else the hammer felts wear out. each time the hammer strikes the string it gets slightly compacted and wears grooves into the hammer felt. As the felts gets harder as a result of this the tone of the piano usually becomes harsher and more metalic. It’s a very gradual process so you won’t notice from one day (or even several months). For a concert grand I’d expect to replace or shave the hammers about every 5 years. for someone’s home piano usually about every 15-20 years.
A brush is the wrong tool for removing the grooves, instead you use fine sandpaper to take off one layer of felt at a time, while maintaining the shape of the hammer. Talk to your piano tech about what you want out of the repair and he’ll be able to help you out. Be aware that ff this is 100+ year old piano the cost of a repair may end up being more than the cost of nicer piano. (based on that kind of maintenance history there are probably also several other issues that should be addressed) Also Piano hammers don’t necessarily have to be replaced. You can usually shave the hammers at least once, sometimes 2-3 times, It all depends on the condition of the felt. This removes the compacted and worn our part of the felt that has the grooves. It’s really impossible to give advice without actually being able to inspect it.