A surprising number of subscribers have asked about the brand and type
of RTV silicone I use, and other questions on its application.

Dow Corning USA were -- unsurprisingly, as silica glass makers -- the
originators of RTV silicones and for 40+ years had a virtual monopoly.
They offer a huge variety. I regularly used their 732 General Purpose
RTV sealant adhesive, a convenient non-slump paste in a cartridge, but
now a slightly better high modulus version is commonly available, 781.

Now that Dow Corning's patents have expired they and several more
companies sell RTV silicone adhesive sealants under others' names as
well as their own.  Any high modulus pure acetoxy siloxane (silicone)
sealant adhesive will serve well.  'Acetoxy' denotes that they cure
simply by moisture catalysis.  They are invariably available in clear,
black and white at builders' merchants and do-it-yourself stores.

Do not use "silicone bathtub caulks" because these often contain
acrylic gels, glossers, extenders, plasticisers, dyes and anti-fungal
agents and are formulated to stick especially easily to smooth non-
porous surfaces and only have a moderate service life.

RTV is _not_  -- and I have never claimed so -- a universal substitute
for all other adhesives.  It is ideal for fixing pneumatics to decks
because it is a tough elastomer which can provide a strong, partable
adhesive seal, but its shear-strength is not as strong as glues which
essentially set hard, so it is not as good as PVA for bonding rubber
cloth to wood when recovering pneumatics.  PVA is best here as it gives
more consistent characteristics than hot glue.

Nor is RTV suitable for rigid wood-to-wood joints, where semi-permanent
bonds are best made with PVA, and permanent bonds with Resin-W type
adhesive or epoxy.  Nevertheless, there are other occasions in piano
and player work where used judiciously RTV can provide an easily
partable resiliant bond.

One of the requirements for conservation adhesives is that they
eliminate the likelihood of damage during subsequent dismantling and
rebuilding.  Hot glue has never met this requirement.  RTV does, so
I have never had any hesitation in using it on top quality instruments,
some in collections.  Those who protest that today's traditional
materials -- such as hot glue, leather and rubbercloth, which are made
very differently now -- are more authentic are just deluding themselves
for the sake of appearance.

Furthermore, despite wide experience in the US, UK and Europe, I have
heard no instruments expertly rebuilt with traditional materials that
perform so well or reliably as those using appropriate modern materials.
The three most admired reproducing pianos here in the UK (one Welte Red
and two Duo-Art grands) which consistently perform impeccably and which
have very high valuations, were rebuilt to the highest standards using
modern materials, including RTV.

Paddy Handscombe
Wivenhoe, Essex, UK

 [ Several Dow Corning silicone sealants are described at
 [ http://www.dowcorning.com/content/publishedlit/80-3258.pdf
 [ -- Robbie