Cracks forming along soundboard shims

[Clark A. Foerster]

A Steinway B from the 20's that I have serviced for about 5 years is beginning
to form cracks alongside many of the about 11 feet of shims that were put in
the soundboard (not by me) about 6 years ago. Cracks are more prominent in the
middle of the board. The owner, having paid a great deal of money for an
otherwise apparently quality rebuilding job, does not yet know of the problem.
I am trying to get an idea of how to understand the possible cause of the
problem, remedy, and perhaps the use of a DC dehumidifier system to prevent a
more speedy disrepair of the board.  I am also concerned that shims I have put
in boards might also suffer the same fate.  I understand that the amount and
viscosity of the glue used around the shims might have weakened the structure
of the wood thus making it less elastic to climatic changes.  But I thought I
would pass this problem by the rest of you for comment.

Clark Foerster RPT