In the digest of 970327 I reported on the effectiveness of some commonly
used pouch sealing materials.  At the request of a couple of subscribers
I have run some tests using PVC-E and  Dow Corning Silicone grease 111.

The PVC-E seals very well: typical leakage is 3-5 cubic inches a minute.
The silicone grease seals only moderately well: 7-10 cubic inches a minute
of leakage.  Both of these materials appear to stiffen the pouches, PVC-E
noticeably more so than the silicone grease.

This now brings me to the real point to this letter.  To report on the
sealing ability of a material I have not seen mentioned before, Dow
Corning  RTV Silicone rubber 734.  This is a thinner version of the
standard bathroom silicone rubber.  It can be used as is or diluted very
slightly with naphtha.

Because this is an RTV (room temperature vulcanising) material it cures
in a few minutes into a coating of pure silicone rubber with an estimated
life of 35 years or more.  What is equally important, however, is that
this material seals better than any other material that I tested:
typically  1-3 cubic inches per minute leakage after one coat, *and* it
stiffens the pouch less than any other material that I tested.  A win-win
situation?

This 734 rubber sealant is available in small tubes at most Dow Corning
industrial stock lists for under $10.  If any one is encouraged to try out
this material, can you let the rest of us know your results.

Philip Dayson