I have tried using the Dow Corning 111 Valve Lubricant and Sealant for
sealing the pouch leather with mixed results.  The leather stiffness
doesn't seem to be affected at all when using this type of sealer but
I have other concerns.

The sealing property seems very good when spread liberally on good
non-porous pouch leather, but when a thinner layer of grease is used,
or the leather is fairly thin, it doesn't always seal completely.  When
first applied, the leather seems well sealed.  When left for a few days
and then put under a large vacuum pressure (50 inches of water), the
pouch leather looses much of its sealing properties.  What I believe
happens is that when the leather stretches under the vacuum, and the
holes also get slightly larger and the grease which was sealing the
hole breaks open and never closes again.

When first applying the grease to the leather, the top surface darkens
and gets sticky.  If left alone for about 1 hour, this stickiness
doesn't go away and you don't see any color changes on the opposite
side of the pouch leather.  This indicates that the grease didn't soak
through the leather.  This is good.

If the excess silicone grease is left on the leather and talcum is
rubbed onto the sealed surface, this just mixes with the silicone.
Placing a piece of Plexiglas on the sealed side of the leather and
rubbing them together causes the silicone and talcum to transfer to
the plastic sheet.  The plastic is now contaminated with this goo and
is very hard to remove.

If you take a paper towel and rub off the excess silicone grease and
then use talcum, then the plastic doesn't seem to pick up the silicone
any more but it doesn't seem to seal as well.

I am a little nervous about using the 111 silicone grease because it
never cures.  If a surface with silicone grease touches another surface,
there is a  good chance that both surfaces will have silicone on them.

I did run tests using RTV silicone rubber with very good results.  This
is the stuff that cures in air and is said to have a 50-year durability
guarantee.  If someone is interested, I can talk about my test results
in another mailing.

Pete Knobloch (Tempe, AZ)