Earlier this year, when deciding which sealant to use for new Ampico
pouches, I set up a little experiment.  I made a block with a pouch
well in it with suction supply and sealed it well with shellac.

I made a square of Perspex (Plexiglass/Lucite) with a nipple which was
connected via rubber tubing to a manometer.  In between the block and
the Perspex I would sandwich the test sample of leather.  Any porosity
quickly showed up on the gauge.  From memory, I set the suction to read
13 inches of water lift which I considered a "medium" level.

I had searched the MMD Archives and come across a post proclaiming
Hydrophane and got quite excited about the product so quickly ordered
some (identical to the picture in the link supplied by Paddy
Handscombe).  I also ordered RTV111 silicon sealant which had also
been recommended.  Plus I had rubber cement on hand.

Well, I treated a patch of tan pneumatic leather with the Hydrophane
first.  Immediately, the results looked excellent and I thought I'd
found _the_ product!  However, when I came back the next day and
re-tested the patch, the Hydrophane had lost essentially all of its
sealing properties.  So I repeated the experiment -- same result!
I put on double and triple applications of Hydrophane and always it
seemed to lose the ability to seal.  The rubber cement and the RTV
sealed well, with the RTV being superior and more flexible from what
I could tell.

Like all new products of this nature, I put some Hydrophane on some
waxed paper to see how or if it dried.  After more than a month it
was exactly as I'd left it.  It would be good if someone else could
repeat this experiment -- maybe with a bubble gauge?

My experiment was hardly perfect in the scientific sense but it left
me with a strong impression that Hydrophane might work well on wet
weather gear but I'm not comfortable using it on pouches.

Stephen Powell
New Zealand Piano Tuners and Technicians Guild
Wellington, New Zealand
pianotec@ihug.co.nz.geentroep [delete ".geentroep" to reply]