Circa 1986, Armstrong A-12 was good stuff. Last time I looked they still
made it, though it would not be shocking if there's been better stuff
made in the past 30 years. Can vary the mix to vary the hard/flex
characteristics. Heat will speed the cure.

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Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.