Allan,

Thirty five years ago, when epoxy was hundreds of dollars a gallon, we
used poly for glassing, never as an adhesive (it was not as strong as a
good glue). The general consensus of the experts was that It should
only be used for glassing on a virgin, stable, substrate which was
mostly plywood back then. NEVER on planking, strips, etc or previously
painted wood, because the bonding strength and sheer strength would not
hold up to the forces which resulted in the expansion of these
substrates or the poor penetration of the previously painted surface.

The first coat of poly was thinned with styrene (the base solvent of
polyester) 30% as I recall, immediately followed by a straight coat that
the glass was laid into. The rest of the buildup was as with epoxy
except you had to work your ass off if the job was of any size. This
method worked ok and some of it lasted at least several decades. The
ones that failed were usually the ones that violated the rules above or
were boats that were grossly mistreated. For instance, acetone was
substituted for styrene which reduced the mechanicals of the poly by
about 20% to 30% as I recall.

About the same time I was introduced to epoxy in the lab at GE (they
could afford it). For the next twenty or so years I waited for the
price of epoxy to come down to my recreational budget level. That was
about 15 years ago and I have not used poly since. As far as I am
concerned, the only justification for poly is in high volume production
molded parts (unfortunately like boat hulls). But even there you will
see the highest quality products using epoxy.

Bottom line. With epoxy at $40 to $50 a gallon, I wouldn't use poly if
it were FREE!

My opinion, worth what you paid for it.

Regards, Ron

I don't recieve e-mail at this address because of spam. E-mail me
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