The player bellows, organ bellows, and large pneumatics we deal with
are made of a 3-ply material that is about the same for a wide variety
of instruments.  Since I have never seen nor heard of this material
being  sold commercially for the construction market, i.e. lumber yards
of the day or hardware stores, I have always assumed that the plywood
was made up by the factories where these instruments were manufactured,
and indeed I have seen the machines and jigs used at the local Wicks
Organ factory where they did precisely that to build consoles and major
panels for windchests and case parts.

This material was glued together with the hide glue of the day.  Over
time it is especially prone to delamination.  While the whole piano
case is layered and glued together with the same glue, I always
wondered why the pianos held together so well for the most part while
the bellows systems so often delaminated after the same number of
years.   The climate these pianos lived in for their lives had a
distinct effect on the likelihood of delamination.   In the damper
climates and in damper basements, the delaminations are worse.

In recent years, I have found that about 60% of player bellows and 80%
of reed organ bellows systems are delaminated to the point that new
plywood is necessary.  This delamination can cause unexpected problems
of leakage,  and I have very rigid standards of how much delamination
is tolerable.  If there is any question about delaminations,
replacement of the wood is the first solution.  I have tried regluing
the delaminated plies, but in so many cases the plies are in several
pieces as well, and the results are time-consuming and are not
acceptable.

Every attempt is made to get new Finnish or Baltic birch plywood to the
correct thickness, and that is usually available.  If the thickness is
off by a 32nd or two, it usually is not a problem.  When it is, planing
or peeling a layer off is not a big deal to do.

Doug L. Bullock
St. Louis, MO