choice of glue

[John Delacour]

At 22:20 16/08/01 -0400, Tvak@AOL.COM wrote:


>I understand that choice of glue often has to do with the ability to remove
>the glue later.  Both of these pianos are old enough that by the time the
>dampers need replacing again, the other parts will be dust, so I'm operating
>as if glue-removal is a non-issue.
>
>I am also replacing the catcher leather on the spinet.  Never having glued
>leather before, would PVC-E be a good choice for this application?

I never use white glue (PVA) except for certain special operations such as 
stepping and backing treble damper strips.  At the workshop I use almost 
exclusively three different grades of hide glue, one named 'Golden Grain 
Powder' for heavy construction work (I can no longer obtain this), regular 
pearl glue - which is the most 'flexible' and convenient for action work 
since you can use it in a variety of consistencies depending on the job -- 
runny and hot for wood joining, thicker and warm for hammer fitting etc., 
and "rabbitskin glue" which is nothing of the kind but simply a high grade 
of hide glue.

The glue (cake, pearl or granules) should always be mixed cold with more or 
less the same quantity by volume of water, covered, and left for some time 
to absorb the water completely and become gelatinous.  With pearl glue, the 
time required is less than an hour whereas the rabbitskin can take three 
hours.  The rabbitskin is more sensitive to its condition and more 
attention needs to be paid to age thickness and temperature than with the 
pearl glue.  Both are more than adequately strong for action work but the 
pearl is marginally more convenient where great strength is not 
required.  Soaking off and removal is also quicker and it is cheaper -- not 
that price is very important in this case.

Once one is familiar with the characteristics and behavior of the different 
grades, all are equally convenient to use and I would use rabbitskin for 
preference.

It is convenient to make up small quantities of cold mixture to avoid 
waiting the soaking time, and these can be stored in the fridge or freezer 
in polythene bags ready for immediate warming and use.

Glue should never be 'cooked' or allowed to stand for long in water more 
than just scalding hot.  If the glue-kettle sings it is getting too 
hot.  So long as the glue is not overheated, it will remain usable for 
longer on the current job, down to quite a low degree of warmth, and be 
reusable.  The glue container should be kept covered as much as possible 
all the time to avoid evaporation and skinning.

I never use either an electric glue-pot or a traditional cast-iron 
glue-kettle except for construction work where large quantities are needed; 
instead I use a either a small glass with tapering sides or a Chinese 
tea-cup.  This is held in a hole cut (very easily) in an old aluminium pan 
lid or biscuit tin lid at least half its sides immersed in a pan of hot 
water below, which may or may not require intermittent reheating.


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If you have not used traditional glue before, it is good to play around a 
bit with different consistencies, temperatures etc. even cooking it and 
mistreating it to see the effect and get thoroughly familiar with it.  Once 
that is done, it is unlikely you will ever want to use any other type of glue.

For permanent, strong and quick repairs (especially for concert work or 
outside jobs) I have found nothing better than Devcon's 5-minute 
epoxy.  This is perfectly transparent and develops a bond very fast, for 
most purposes allowing use within ten minutes.  In England I pay twice the 
price I would pay for the well-known alternative but consider it worth 
every penny.  Of course I would never use this for general repair work.

PVA or white glue can be soaked off but a white residue also needs to be 
removed and the stuff is generally not nice, though it is obtainable in 
many grades of strength and 'hardness'.  I would not use any of them however.

One of the other wonderful things about real glue is the way it cracks 
under the effect of alcohol!  enabling apparently the strongest and widest 
bonds to be broken, whether piano ends or pin-blocks.  When choosing your 
glue "think of the next man".


JD