Andy Taylor wanted to know about the life of rubber cork gasket
material, particularly if it used as a flap valve.  Like many
materials, this stuff is made in many grades of quality.  Twenty years
ago, some of it was in circulation that was just horrible.  It was not
air-tight and it broke apart easily.  This stuff generally had a
reddish color.

I visited with several major gasket manufactures in the Chicago area
seeking information.  Through that research I discovered a product that
is excellent and undeserving of the bad rap "don't use this stuff"
label.  Armstrong, the big name in flooring, and cork, etc., makes a
product called "DC-100" in two thicknesses: 1/16 inch and 1/32 inch.

This composite cork material is perhaps the finest gasket material
suitable for player piano work that money can buy.  It will never go
bad.  Any type of glue can be used and it is 100% airtight and unlike
cork, it will stay that way.  It takes almost no visible permanent set
as does pure cork.  As a gasket material, it far superior to cork,
leather, and blotter paper.  It's the best.

I do not think it should be used as a flap valve as it might be noisy
and might not stand up well to mechanical movement.  Flap valves must
be stretched to seat.  This material is meant to gasket mating
surfaces.

Gasket suppliers also stock competing brands that match "DC-100" in
specs.  They are probably just as good as the Armstrong product.  When
ordering, specify that it must be just as good as DC-100.  DC-100 is
expensive and is sold in 36" x 36" sheets.

Bob Taylor