felt separating from hammer core

[Ted Simmons]

I am going to service a piano where the hammer felts have come loose from
the core on one side.  I tried contact cement and superglue with no
success.  My method is to apply the glue then tie the hammer tightly with
waxed string. I leave the string there so the glue dries thoroughly until
the next appointment.
At the next appointment I remove the string and the hammer felt pops back
up.  I think the superglue wicks up into the felt and contact cement just
doesn't have the strength.  Any suggestions would be most welcome.
    ted simmons
    independent piano technician