[CAUT] glues, Poletti

[Ted Sambell]

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
----- Original Message ----- 
From: "Richard Brekne" <ricb at pianostemmer.no>
To: <pianotech at ptg.org>; <caut at ptg.org>
Sent: Wednesday, November 28, 2007 2:40 AM
Subject: [CAUT] glues, Poletti


> Hi Anne
>
> Creep in conditions like you mention seem quite easy to understand.  There 
> is a kind of shear stress on a hitch pin rail that is glued to a 
> soundboard. But there is another point from his site I found very 
> disturbing . The assertion that Titebond and similar glues never really 
> harden and impart (to some degree)  kind of damping effect, absorbing some 
> of the vibration energy instead of either reflecting or transmitting. This 
> has immediate implications for modern piano building as well as older 
> instruments.  I'm not so sure how much a problem Creep is in situations 
> where there is not immediate and significant levels of shear stress on the 
> glue. But I'd like very much to hear more in depth comments about all this 
> in general.
>
> I'm not sure I'd have a problem using Titebond to fix a broken shank out 
> on some field repair job.  But thats not really what I was talking about. 
> When in a restoration shop one has a variety of choices at hand.
>
> Cheers
> RicB
>
>
>    Ric wrote:
>
>        Hi Folks
>
>        Reading in one of Anne Ackers i found a reference to the website
>        of one
>        Paul Poletti who has a side dedicated to glue. Please look over the
>        following and provide comment.
>
>        Thanks
>        RicB
>        ******************************
>
>
>
> He's absolutely right.   Most harpsichords built with aliphatic glues in 
> the 1970's and 1980's demonstrate cold creep very nicely with the 
> shrinking of the gap as the soundboard creeps forward, e.g.
>
> Besides, hide glue is so EASY to use.   If it stinks, you're using bad 
> stuff.
>
> Anne