[CAUT] glues, Poletti

[Richard Brekne]

Hi Ted, and others.

I just had a long discussion on the phone with a prominent rebuilder I 
know stateside who had a completely different take on all this.  For the 
first he discounts immediately the problem of sound transmission through 
glues like Titebond.  He points out that the wave lengths of frequencies 
transmitted are simply far to long to be affected by the difference in 
hardness between a so called natural glue and a glue like Titebond. And 
as to creep... he is of the opinion that the glue SHOULD allow for a bit 
of creep back and forth.  The soundboard splitting problem you cite 
below may be an example where his logic makes sense.  If the glue gives 
in shear direction a bit back and forth, then effectively it works as a 
kind of shear stress buffer, allowing the soundboard to expand and 
contract a bit more on the ribs then a glue with more shear holding 
strength.

As to usages such as hanging hammers on shanks. I've always used a 
Titebond like glue for this job myself.  I brush the inside surface of 
the hole in the hammer first and let that soak a few seconds while I 
brush on a bit of glue on the shank.  Getting a nice sized collar has 
never been a problem.  I've never encountered a real problem removing 
hammers glued with this kind of glue either.  YMMV.

Bushing however.... Well... tight bond is just plain too much a pain in 
the patootey to get out of the mortice... different situation entirely. 
Fish glue or something similar is just the thing... especially in a 
University setting where bushings can need changing every couple years 
on some instruments.

Cheers
RicB



    I read somewhere that all glues will creep to a greater or lesser
    degree.
    When I was teaching at George Brown College, it was impractical to
    have a
    large number of glue pots for hammer gluing, much as I would have
    preferred
    hide glue, so we used Titebond. It was much harder to extract
    hammers from
    the shanks with this than those glued with hide glue, though ten
    minutes
    with a heat gun let them be pulled off readily.The soundboard splits we
    commonly encounter in old pianos are mostly not true splits at all, 
    but are
    separated joins,  thus showing that  creep has occured by shearing
    at the
    ribs. It can be assumed that most of these soundbards were glued
    with hide
    glue. It is just as well. as if the joints hold, there would be true
    splits,
    which would be very difficult to shim unless the grain is very
    straight. I
    enjoy working with hide glue, but it is more demanding. It must be
    carefully
    controlled in viscosity, though this is also an asset;  large work
    such as
    cabinetry (and soundboards) should be heated, clamps prepared ahead of
    assembly and applied very quickly.I have taken to using fish glue
    for key
    re-bushing;, but found it necessary to prime coat the  mortices
    first with a
    50-50% dilute with water. It is slow setting, but will take hold
    quickly.
    Fish glue is easily reversible with the usual mix of warm water and
    a little
    wallpaper remover. It is availabele from Veritas. There is a small
    bottle
    with a brush in the lid which is ideal for light field repairs, and
    refill
    17oz. bottles. I have seen failures with hide glue through lack of
    understanding. One new grand I saw had a large number of loose
    hammerheads.
    The glue collars were all near black, indicating the glue had been
    boiled.
    Hide glue must not be heated above 150F. 140F to 145F is considered the
    proper range. Bill Spurlock recommends the use of a Rival Express 
    Hot Pot
    and setting its temperature with the aid of a candy thermometer. I
    saw these
    recently in Wal-Mart, and think it a great idea. They cost around $15
    compared to $100 or so for a dedicated glue pot.

    Ted Sambell