In the book, "A Treatise on the Art of Pianoforte Construction", by
S Wolfenden, is a short chapter entitled "Glue and it's Economical
Useage."

Wolfenden was the technical expert for the Aeolian Company's UK
operation (known as The Orchestrelle Company) who of course made
Weber pianos, etc., at the Hayes factory just west of London.  He was
supremely competent and redesigned the structure of their range of
pianos, which are known as Wolfenden models to folk in the trade who
can spot the differences.  When you encounter a "Wolfenden" designed
model your ears tell you straight away that the man knew what he was
doing.

Wolfenden wrote his book in 1916.  As a technical text on piano
construction and the science behind it, there is probably little to
surpass it even nearly a century later.  His chapter on glue is in
relation to piano making and not specifically gluing or rebuilding
pneumatic components, but the science is still one and the same.

At the time the chapter was written Wolfenden had over 50 years
experience working at the forefront of the leading piano manufacturers,
so we may take it for granted that if any one person knew what they
were talking about then Wolfenden certainly did.  You probably cannot
get a more definitive answer than this -- from a man who spent more
than half a century working with the stuff daily.  There is a lot to
be learnt from this chapter.  Please don't just dismiss this and email
everyone telling us all you've "worked in player repair for as long as
Wolfenden and...," blah, blah.  This guy clearly saw more pianos and
parts than everyone in the MMD put together ever did.

For those who advocate using hot glue here is how it is best used.
For those who advocate synthetics read the whole chapter and especially
the closing lines.  Although synthetic glues were not available when
he wrote, he did state that there was a need for something with the
properties of today's synthetics.  All this was of course years ahead
of their invention and introduction.

As with any glue one should only use it if it does the job correctly.
Clearly, then, old hot hide glue does the job and also certain specific
synthetics do the same job also.  Why might a person want to use glues
with the properties of modern day synthetics perhaps?  Read the chapter
and see if you agree with Wolfenden!

I've scanned the chapter and you can read it at  www.themodist.com
(click on the "texts" link).

Sincerely
Adam Ramet