Gaskets keep everything nice and tight. They keep the suction in where you want it, and the atmosphere out. Since all valve boxes are made of blocks of wood, and even well-mated wood surfaces are not airtight, there must be a membrane of some sort which is suitably compressible, but also durable.
The traditional candidate is split leather. When leather of proper quality and consistency is used, it does both jobs well, and leather to wood with hot hide glue is a match made in heaven. There simply isn’t a better way to work other than the original way.
However, there are alternatives.
When I say alternatives, I want to stress I am not taking about the adhesive part! For my opinion on glues, see previous post here.
I was speaking of a “modern” gasket material of neoprene. Plastics get a bad rap in the piano industry sometimes, because in the beginning, the technology was inferior and the product didn’t age well (plastics were introduced into pianos as early as the 1930’s). However, plastic materials have come a long way, and like every product there is a range of quality.
Traditionalists will turn up their noses at this idea, but that’s fine. Tradition has its place, and I respect it where I feel appropriate, but this doesn’t prevent me from trying new things.
In the case of neoprene, for a material that was modestly cheaper, easier to source, slightly easier to work with and – most importantly!– well-performing as leather, that seemed good enough for me. Time will tell!
My main concern with this type of product in the long term would be elasticity (being permanently compressed and not expanding in drier weather), and structural integrity (starting to disintegrate over time). On the question of integrity, since a gasket is –by definition– always sandwiched firmly between two pieces of wood, the oxidization problems should be minimal.
The material comes in sheets and you just cut what you need, in the most efficient way you can manage. For cutting straight lines I use a steel rule and a rotary cutter, on a cutting board designed for the cutter (“self-healing”).
For punching holes I use a handheld punch, which works well for screw holes (the most common kind). For anything larger than that, you really need a punch set to do a neat professional job.
For small and medium surfaces mark all holes on a given side with chalk (lightly) and then dry fit the gasket to the surface. The perimeter outline can be rough at this point, doesn’t need to be perfect now. Release the piece and place the gasket on a punching board. The cutting board worked for me for this material, because it’s so light, you just press it out by hand. I would not have used a hammer to drive the punch on my nice cutting board!
Then do the screw holes, however you want. When all done check against the piece, and assuming it’s good, go ahead and glue it on real good (the neoprene I use has two different sides, it’s the “skin” side which gets glued down).
Finally cut away the perimeter edge with a pair of shears or long scissors. Easy!
The only thing to watch for is that the thickness tolerance is kept faithful, when you replace gaskets. If you are putting neoprene in place of a gasket that was originally designed to be leather or blotter paper, the compressibility will not be identical, so this is something to keep in mind. If you are not duplicating the original in terms of material, you should still attempt to match it in terms of dimensions, wherever possible.
Gaskets can be made from any number of things, but traditionally it has been leathers, cork, blotter paper or other cardboard type papers. You can choose to use any number of solutions, but don’t use the wrong material for the wrong reasons.
The thing about quality leather is that it is getting harder to source. It’s just another one of those commodities that has become more scarce, for several reasons. That was part of my decision to go with neoprene.
But using cheap and inappropriate materials only to save a few nickels and a few minutes is false economy. Spare a thought for the person who will have to do the next restoration, it may even be you! Trying to scrape off disintegrated plastics mixed with modern glues is truly drudgery of the worst kind. Don’t let it be you!
No photos this time, but I will illustrate gasket use in the following post!