"Jere Lull" wrote

The problem with epoxy is that nothing sticks to it well -- the best you
can get is a mechanical bond. If you can be assured that you never will
have to deal with an area again, go with epoxy, but I'll use a good,
fresh polyester for everything else as the next layer will slightly
chemically bond to the previous one to give a greater grip than a pure
mechanical bond.


Jere,
I am puzzled by the above statement. It is not what I thought was generally
accepted.

One of the problems with fibreglass repairs done using polyester resin, is
that secondary bonding (new polyester to old polyester) has poor strength.
This is generally accepted in the industry. Epoxy resins have superior
secondary bonding strength for fibreglass repairs. But, due to cost, most
fibreglass repairs are done with polyester.

When it comes to blister repair, 2-part epoxy pastes are the norm. Even the
website you referenced says that:
http://yachtsurvey.com/BlisterFail2.htm

If your concern is overcoating an epoxy barrier coat, then following a
manufacturer's procedures is important. Interlux have a system for their
Interprotect barrier coat which if followed works well. It should be well
documented on their web site.

It was interesting to read the yachtsurvey site. He is adamant that boats
should not be sandblasted. There is some basis for this, because often the
sandblasting only exposes some bubbles, but in other areas it just removes
more of the gelcoat leaving unexposed bubbles below. Peeling may be better,
but sometimes this process is not available or is just too expensive. I have
personally seen medium to heavy sandblasting , followed by grinding of
individual blisters carried out successfully (maybe 30 or more boats) - By
that I mean 15+ years with no blisters re-appearing. In all cases, the
Interprotect system was used with either Micron or VC-17 antifouling.

I believe that one of the biggest reasons for blister repair failures is not
allowing the hull to dry after sandblasting or peeling. In southern climes,
this can be almost impossible to achieve without building a dehumidified
enclosure. We have probably had much better success because in the North, it
is very dry in the winter - and the boats can dry for 5 or 6 months because
owners are not too anxious to go sailing Nov-Mar!

Even today, anyone buying or building a new boat should consider having 4 or
more coats of epoxy applied before applying antifouling. Follow paint
manufacturer's instructions for hull dewaxing and other preparation. Boats
in our area treated this way have NEVER had blisters.