Cracks & Soundboard Shims

[PIANOBIZ@aol.com]

>Subj:      Cracks forming along soundboard shims
>Date:      96-02-21 16:42:00 EST
>From:      cfoerst@cello.gina.calstate.edu (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

Hello  Clark,
There are many reasons why a crack could develop beside the shim.  One the
shim could have been wet when installed.  Some forget to dry the shim along
with the board before doing the shimming. Two, some use inferior material for
the shim such as wood putty or epoxy.  These do not expand along with the
wood through seasonal changes and very soon leave a gap.  Three, traditional
V-shaped shims lead to very little contact between shim and board, usually
obvious if viewed from the underside of the board.  Fourth, and most likely,
the soundboard was not protected from excessive moisture.

I'll share with you my theory on the crack itself.  The first stage of a
crack is actually over compression.  (This is a New England developed theory)
 I don't know about other climates, but here, if you can keep the board from
over swelling in the summer, you'll have a 100% success rate.  It does make
sense. The wood swells and over compresses during the summer.  We don't
notice the damage done by the over compression until the winter when the
moisture leaves and the over compressed wood does not return to its original
state.  Consequently we associate cracks with the board being too dry when
we're actually seeing the summer damage appearing in the winter.

Therefore, I closely monitor the surface of the soundboard with my hand
during the summer.  If the board starts to develop the rolling hills of
Vermont feel as I run my hand cross grain, I sound an alarm and quickly get
some more drying power under that board.  It goes right back down.  Another
board saved!

Clark, you might be wondering if there were anything you could do to reverse
this problem.  In my opinion no. Once the damage has been done, all you can
do is wait till the next rebuild.  You can arrest any further damage by
installing a complete Dampp-Chaser installation.  For a Steinway B in New
England, I install two buckets and at least three drying rods, four is
better, totalling 138-163 watts. Surprised?  It works.
(BTW, I think the kind of glue used for the shimming is of little
significance)


David Sanderson
Littleton, MA
Pianobiz@aol.com