There is a possibility that hot animal glue may be banned through
controls over infectious proteins.  Already most traditional methods
of tanning are banned because of the noxious and toxic chemicals
previously used (including, up to WW2, I kid you not, dog sh*t).

Traditional hot glues were used mainly because they were so cheap,
and huge quantities were used in piano and player manufacturing
rather than other adhesives such as casein or latex (which were
available a century ago) or fixings such as screws, all of which
were significantly more expensive.

Hot glue is actually relatively unstable, softening with humidity
and tending to crystallise and become brittle if chilled too fast,
desiccated, or subjected to repeated stress.  (Hence the need for
tropicalised pianos.)  Hammer heads stuck on with hot glue, for
instance, are often found to be quite loose, which leads to odd sounds.
Therefore few musical instrument manufacturers and professional piano
rebuilders have used hot glue for some time.  Adhesive technology has
advanced enormously since WW2, and there is a vast range of more
reliable permanent and semi-permanent types available.

Note that "white glue" is a meaningless term.  Many glues are white
when liquid but utterly different.  PVA is polyvinyl acetate, water
soluble; casein is milk protein and usually water-insoluble when set;
Elmer's glue and Phenoseal are water-insoluble PVC, polyvinyl chloride
and phenolic resin(!).  Copydex is water-insoluble latex rubber.  Some
craft glues are PVA but many are starch gels not strong enough as
structural adhesives.

All the above glues, including hot glue, are organic compounds.
RTV (room temperature vulcanising) silicone sealant adhesives are
polymerising silicones, organic compounds of silicon.  Silicones have
been around since the late 1940s and are very stable.  Until relatively
recently they were very costly.  Normal RTVs set not by solvent
evaporation, but through catalysis by water vapour, whereupon they
liberate a small amount of acetic acid (vinegar) vapour, so they are
very tolerant of damp surfaces.

_Some_ bathroom sealants are based on RTV silicones, but frequently
contain extenders, glossers and antifungal additives.  The best RTV for
attaching pneumatics is pure, colourless RTV silicone adhesive sealant
such as by Dow Corning, General Electric, or Würth in Europe.  (Black
RTV also has its uses.)  It is available in low-modulus and
high-modulus versions.  High-modulus is preferable, as it is somewhat
less elastic, but the difference is small and both work well if the
adhesive layer is kept as thin as possible -- as with any glue, the
strongest joints result from the thinnest unbroken layer of adhesive,
since any mechanical leverage is minimised.

Normal RTV comes in the usual cartridges as a 'non-slump paste',
ideal for player work.  The nozzle provided gives uncut a worm of
RTV about 2 mm diameter.  After marking and preparing the deck and
pneumatic boards, the best technique is first to apply a worm of RTV
in a complete circle round the hole in the pneumatic about 3 mm from
its edge.

The intention is after the pneumatic is pressed into place to achieve
a perfect annular seal with the adhesive just exuding over the edge of
the hole yet not blocking the windway.  Next apply a line of RTV near
the perimeter of the pneumatic board and perhaps a few zig-zags where
it will meet the deck face, remembering it may overhang the deck.
There is no need to cover the whole board.  The 'skinning' time of RTV
is about 20 minutes, so there is no need to hurry.

Now place the pneumatic on the deck in substantially its final position
and press it down firmly with a slight 'shimmying' motion, finishing in
the correct position.  It will grab excellently.  If RTV just exudes
from the sides and extremes when it is post-card thin you've probably
used the right amount.  To check, first time, you can immediately lift
the pneumatic carefully off the deck and ascertain the displacement of
the RTV.  Remove or add a little more RTV if necessary and shimmy it
down as before.

There is no need to use clamps or weights.  A pneumatic is happily
shimmyable for perhaps 10 minutes or so; if you should inadvertently
dislodge it after that, remove it, scrape off all adhesive and stick it
down again.  Surplus adhesive is easiest to remove when set, when it
can be cleanly scored with a sharp blade and peeled away.  RTV is
strong in a few hours, fully set in 24.

If possible leave the first trial overnight and check how strong your
bonding technique is by trying to prise the pneumatic off the deck by
hand; it should certainly be no easier than originals hot-glued with
leather or card gaskets!  If it comes away too easily, decide where to
place more adhesive worms next time.  Then peel off as much of the set
RTV from the boards as possible, eliminating all loose areas or lumps
and re-glue the pneumatic down.  There is no need to achieve a clinical
surface -- the new RTV will make a perfect seal and bond.

RTV is thus very forgiving and certain to use.  Though it bonds very
strongly, removing a pneumatic for any reason could not be easier or
safer.  Simply slide a thin palette knife or blade through the RTV
between the boards.  Clean the boards as before and re-glue.

RTV will bond to dust-free plain wood, and will get into the interstices
of the grain, but actually no deeper than hot glue, so it requires less
sanding to remove all traces, after which any type of glue can next be
used.  But I deprecate sanding to remove old cloth and glue because of
the damage and mess it causes.  Old cloth can be removed by peeling or
heat, and a solution of PVA will melt old hot glue and allow it to be
scraped off easily.  Then a wipe with a damp rag and a light smoothing
readies boards for re-gluing.

RTV bonds better to and is easier to remove from glazed surfaces than
plain wood; smooth old hot glue will do, but PVA is best.  One of the
best makes in the UK is Unibond.  It can be used neat out of the tin,
but a little added water makes it wet better for glazing.  If necessary
you can later damp PVA, when the whole lot will wipe away revealing
sound plain wood.

I have rebuilt a number of instruments previously messed up with
various glues, including hot glue, but am never fazed.  They just
require the right solvent and/or removal technique.  PVA should not
be used for sticking pneumatics to decks because of the difficulty of
wetting joints to break them.  Even so steam or a solution of PVA will
loosen them eventually.

However neat Unibond is excellent for covering pneumatics because it
does not grab too fast and allows the cloth to relax just enough to
prevent overtight corners which affect the force of the pneumatic and
wear through quickly.  It never flakes or sets totally hard so no sharp
edges will cut the cloth, and the hinge overlap remains flexible.
Stick all the open ends of a set of pneumatics first, then one side of
all, and so on.  You'll achieve very consistent characteristics without
much practice.  And again later if necessary the cloth can be peeled
off and the PVA easily removed by damping.

Personally I don't get hung up on the market value or intrinsic worth
of any players or how they look, as long as they play as intended.
They were, after all, only luxury consumer goods, sold for entertainment.
Nevertheless I would never make any irreversible changes to any
instruments.

Paddy Handscombe
Wivenhoe, Essex, UK