splinter, the hardness of varnish can vary quite a bit in either interior or exterior formulation. It is dependant on what it is formulated for. Good gym floor finishes are usually polyurethane and alkyd resins that produce a hard product and made to walk on. One of the advantages of hard finishes is that they sand better. I dont walk on or sand rod wrap coatings and see no advantage of using a harder finish.

A good spar varnish is made with tung oil and phenolic resin. Modern spar varnish can also contain alkyd resins. Good spar varnish is formulated for outdoor use, resists cracking and crazing has high water resistance and other qualities that made it the traditional varnish for rods. I would much rather use spar varnish than a hard gym finish on a rod.

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Joe