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When do you decide to change hammers on a piano in a domestic situation ? it sounds nice but the hammers have there for 30/40 years now.

you can decide for yourself, fuller tone, more rich and better dynamics is what you obtain with new hammers

the felt of the 30 40 years old hammers is dry and loosed its resiliency, the scales that hold the fibers together fall and turn to dust, this is mosty because the felts used where bleached too much and too much heat was used in the pressing

also the felts where often pressed much to obtain the wanted hardness (asked by the hammer makers) but if the melting of the fibers is not done to the max that sort of hardening get disrupted easily when the hammers are voiced.

Old hammers if thick enough always can be impregnated and voiced again, but the resiliency then is not allowing a very rich and transparent tone, more a tone with an acceptable power and dynamics but a 'simplified spectra'

as the cost of installing new hammers is not so cheap, all depends of the quality of the instrument

on a vertical, keeping the original shanks can help for the cost as the job is done faster then; but it is less precise, the strike line cannot always be kept ideal (there are always small differences in bore and shape with the new heads)

with some major brands, buying a pre glued set yet on new shanks can be almost the same price than buying a set of good quality heads only.

Thanks for that, there are grooves in the hammers but it still sounds very nice, They are actually selling the piano and I'm trying to access its value and if its good enough in its present condition for another 20/30 years to recommend for another family.

Hammers are worn out when they can no longer be tone regulated for good tone and touch. It doesn't matter what they "look" like. Wool felt is a very long lasting material. It can endure centuries as long as the moths don't eat it and the sun doesn't burn it.

That sound as some old pianos dealer speech!

The fact is that from 50 to 90 the felts we used to see where hardening and loosing resiliency in time.
To the point a study was done as to find the cause.

At the same moment older hammers where doing quite well in regard of more recent.

Thy discovered that both the felting process and the hammer pressing where responsible to some amount.

Since then we have (hammer) felts that get better and better.

Olek, I stated a first principle regarding the utility of piano hammers. What is wrong with that?

I had a conversation about this very issue with Jack Brand several years ago. I was surprised that Jack claimed felt does not necessarily deteriorate with age, but can actually improve.

My own experience tells me that it depends on the particular hammer. Some of the old turn of the century pianos have these big, seemingly soft hammers that can put out surprisingly good tone. Of course its getting rare to find a set that aren't very worn, but they are still out there. We are working on a 100 year old Sohmer right now, and the hammers shaped up great!

I wonder if hammers can be a bit like paper: if acids are left in the manufacturing process it can break down the fibers over time.

Yes that is what surprised the German hammer makers just before the 90'

they receive their hammers about 30 years old to be re felted (keeping the moldings glued on the shanks) and did not understood wht the felt was brittle and hard at the same time (or sometime very soft but weak)

pics with microscope show a lot of debris (scales) so the fiber did not stay interlocked well

A scientific study was done (I d like to see it, if some German speaking can find a link to order it ?)

AS I was told, too much lanoline was extracted in the washing, not enough reinsered later

too much heat, making the fiber more brittle and less springy

Plus the fast pressing with powerful presses that can disrupt the felt, and the drying of glue with micre waves

sort of things that Renner and Abel do not today

Also at those times, VFG which was not specialized in piano hammers felt, was "obliged" to produce, as the traditional Wurzen factory was out of production during the communism years.
So they have also benefit of those studies, and begin to try to make old type felts