At the risk of offending all those who swear by shellac as "the best sealer" just because it has been around for a long, long time and certain companies only use shellac as a sealer, allow me to present a few of my findings and opinions.
Recently, I poured an 1/8" of Phenoseal into the lid of a plastic container and let it dry overnight. The next day I carefully removed the 'film' and tortured it for a couple of days. I started by placing it under a 140 degree heat lamp for three hours. Then I put it in the deep freeze at zero degrees for 24 hours. Then I put it in a 750 watt microwave set to High for a minute.
Guess how it looked and felt when I was done... Other than a very slight discoloration, which was caused by the microwave, it looked and felt exactly like it did after it dried. It was still as flexible as before testing was started, it had no cracks, it wasn't 'sticky', it didn't melt, and it was still 100% air-tight. Try that with shellac....
I started using Phenoseal just over ten years ago when I was desperate to fix internal leakage in Simplex block valve/pneumatic units. After trying shellac, which seemed to take forever to dry, I called Durrell Armstrong and he suggested that I try Phenoseal. After seeing how it soaked into the wood, and dried in less than an hour, I put the shellac away. From that point forward, I tested it on various devices and materials to find out the limits of this great product. I've even used Phenoseal to seal the windows in my home instead of spending hours scraping off the aging caulk and then re-caulking.
Unlike shellac, which cracks as it ages and therefore leaks over time, wood sealed with Phenoseal will NEVER leak unless the wood cracks badly* (see note below). Phenoseal also works as an excellent sealer around the edges of bellows, where air can seep through the cloth. Phenoseal is so thin, it actually seeks out and fills tiny cracks in wood that are invisible to the naked eye. When used to fill larger cracks, it creates a 'flexible' repair that will compress and stretch without breaking. This is especially useful when repairing cracks in the windchest of a 100+ year old reed organ, or other piece of wood that isn't under constant stress. (In other words, it isn't necessarily a strong glue, although it does have some of the properties of glue.)
*Note: Wood sealed with multiple applications of Phenoseal will not leak even if the wood develops small cracks. This is because Phenoseal stretches. Try it yourself. Coat a piece of veneer with three coats of Phenoseal and (after it's dry) crack the piece of veneer in half. It won't come apart on its own. You have to physically pull it apart. That's because the Phenoseal is holding it together. Try that with shellac...
Phenoseal also works as a great leak detector. Painted on the surface of aging bellows cloth while vacuum is being applied, it gets sucked in through the microscopic holes in the rubber layer. And, since Phenoseal is translucent white in color when wet, the area where the air-tight layer has good integrity stays milky-colored while the damaged area quickly returns to its original color, showing you exactly where it's leaking. You can also apply positive air pressure to the bellow and the Phenoseal will bubble where the air is leaking out. This can also be done with wood. In fact, that's how I discovered that it was air leaking through the wood in the Simplex valve blocks.
In closing, Phenoseal is also easy to use and clean-up is a snap because it's water soluble. So, all you need is hot water to clean the brushes or containers you've used to apply the product. All-in-all, Phenoseal is so much better in so many instances, and it can do so much more than shellac ever dreamed of doing, that I'm surprised that anyone has anything negative to say about the product. Phenoseal is available at Player-Care.com. See link below.
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407 19th Ave, Brick, NJ, 08724
Phone Number 732-840-8787