One advantage to adding a barrier coat even if there are no blisters, is
that you apply the first coat of bottom paint while the barrier is not
completely set, and you get a chemical as well as a mechanical bond.
This will improve subsequent bottom paint adhesion far into the future.
Barrier coat adheres a lot better to gelcoat than any bottom paint,
regardless of surface prep.
Bill Bina
On 12/23/2015 9:47 AM, Chuck Gilchrest via CnC-List wrote:
Hi Danny,
Can I ask who did the walnut stripping on your boat and at which
yard? I’m having my “new” 1983 Landfall 35 brought down from the
North Shore of Mass to the South Coast in early January and the bottom
paint is flaking off in chunks, revealing the shiny original gel coat
underneath in most places. I would say that the paint over shiny gel
coat method was not terribly effective for adhesion.
Speaking to the service manager at Concordia about soda blasting, he
tells me that the soda medium leaves a very rough finish on the bottom
that takes a significant amount of labor to prep the bottom afterwards
to allow bottom paint go on nice and smooth. Perhaps he was also
implying that the boat should have a barrier coat added as well…
either way, with soda blasting and subsequent bottom prep, we were
talking in excess of $5000.
With that info, I had planned to chip off as much of the old paint as
possible, sand down the rest using and orbital sander with a vacuum
attachment, leaving just enough “tooth” on the gel coat hull surface
to repaint. It would be a lot of work, but I could do it in my yard
and build my upper body strength at the same time!
However, the walnut shell medium sounds like it may be the ticket if
it is less invasive to the gel coat than soda blast and if I basically
want to start with a blank canvas of a hull to prep and paint. Would
love to hear from others that have used the walnut shell method and
what they’ve done to prep afterwards.
Best,
Chuck Gilchrest
S/V Half Magic
1975 25 Mk 1
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