PVC-E (polyvinyl chloride emulsion) compounds, such as Phenoseal,
usually contain water as a dilutent, but as they 'dry' by evaporation
they become water insoluble.  In the UK we know this type of adhesive
as 'Resin-W' for making strong waterproof joints in woodwork.  Most
restorers will know how appallingly difficult it is to separate and
remove such 'white glue'.

The only place for PVC-E is where parts will never need to be separated
again, such as in split hammer shanks.  In such applications it is
superior to animal glues because it does not crystallise with time,
which renders them more prone to shock failure.  Just occasionally
shock failure is a useful characteristic: it allows striker pneumatics
to be cracked off stack decks for instance.  But crystallisation over
time and subsequent flaking are what also make animal glue and shellac
such poor and unpredictable sealants by today's standards.

A safer and more effective adhesive and sealant is simple PVA
(polyvinyl acetate) which has almost identical properties to PVC-E but
always remains water soluble.  Deep PVA bonds may need soaking to part,
just like animal glues.  But PVA is easier and cleaner to remove.  No
need for sanding with possible damage to the wood and all the sticky
smelly protein dust.  Just dampen PVA with hot water containing a
little wetting agent (such as dishwashing liquid) and after a few
minutes it will scrape away cleanly leaving a perfect surface for
re-sticking.

I use it invariably for recovering pneumatics, because is allows
accurate positioning, 'grabs' quickly enough, yet lets the cloth relax
nicely, so all striker pneumatics for instance come out with the same
tension and characteristics.  And again, it's easy to remove cloth and
adhesive and recover when necessary.

PVA is also the perfect air-sealant and pre-treatment for deck and
pneumatic boards, especially where RTV silicone is to be used as the
striker pneumatic adhesive.  RTV is without doubt the surest way to
stick pneumatics to decks: it allows accurate positioning and creates
a perfect bond and gasket every time in one go without the need for
clamps.

Remember that, as with all adhesives, the thinner the layer, the
stronger the bond.  Surface pre-treatment with PVA (allowed to dry)
lets RTV achieve the strongest bond and prevents any damage whatsoever
to the wood.  RTV used in this way allows pneumatics to removed safely
with minimal force using a thin blade.  Remaining RTV will peel cleanly
off the PVA substrate, which itself can be dampened and removed if
required.

It's worth noting that many of the canvases of the world's oldest and
most valuable oil paintings are impermanently bonded onto new canvas --
're-lined' -- using PVA.  A pretty good recommendation.

Patrick Handscombe
Wivenhoe, Essex, UK