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MMD > Archives > August 2000 > 2000.08.01 > 11Prev  Next


Dow Corning #733 as Leather Pouch Sealant Only
By Pete Knobloch

I agree with Randy that the only color that should be used is the
clear silicon rubber.  But putting this stuff into an organ should be a
crime.  I haven't worked on organs but I would think that RTV would
_not_ be the glue of choice for sealing air leaks between components.

What I should add is that this RTV is extremely difficult to clean off
of porous materials such as wood.  It sticks to metal very well and
doesn't always come off of the surface.  You may have experienced it
pealing away from wood or metal but this might have been because the
surface was not cleaned properly.  I hope this is the case for this
organ.  When it comes to sticking to wood, it seems to peal up easily
where the thicker layers are found but adheres to the wood and just
rips apart where thin layers are encountered.

RTV silicon rubber also has the property of other glues not sticking to
it (except for itself).  When gluing any pouch lifters to a RTV sealed
leather, you must keep the leather clean where the other glue is to be
used.  Masking tape punched with a hole punch and placed in the center
of the pouch leather works well before it is sealed.  This leaves a
clean unsealed area in the center of the pouch so that hide glue can be
used to glue the lifter or the value stem.   I have heard other people
using more of the silicon rubber to glue down the lifters onto the
leather but I would test this before doing it.

I don't see any problems when using silicon rubber as a pouch sealer.
Scraping the top layer of sealed leather with a razor blade removes the
RTV sealer which is only sticking to the top layer of the leather.  The
bottom portion of the leather is untouched by the RTV and can be
re-glued without any problems.  I have tested this and haven't found
any problems.

When sealing the pouches, use these rules:

1. Glue down the pouch before sealing it.

2. If a pouch lifter or value stem is to be glued to the leather,
use masking tape dots to keep the RTV from contaminating the gluing
surface.  Similar to using rubber cement.

3. Seal only the movable surface of the pouch.  The outside glued
surface is sealed by the hide glue and doesn't need sealing.  If just
one pouch has to be removed later, it can be easily removed.  Just cut
out the problem pouch and glue in the new one without worrying about
having to remove the top layer of RTV sealer.  This could be impossible
in many cases since the gluing surface of the pouch leather usually
overlaps the adjoining pouch.

4. Thin down the RTV silicon rubber using naphtha or some other
thinner.  It should be the consistency of thin maple syrup.

5. Make sure that you protect areas from accidental drips.  You don't
want the uncured stuff to get onto the wood where you will be needing
to glue later.

Pete Knobloch


(Message sent Tue 1 Aug 2000, 17:49:11 GMT, from time zone GMT-0700.)

Key Words in Subject:  733, as, Corning, Dow, Leather, Only, Pouch, Sealant

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