You are supposed to do repairs like this from the underside. Not
breaking the outside skin.

So, what's to paint, except the INSIDE?

wrote:
A small 2-square-feet area around an inspection hole on the deck of my
fiberglass boat is kind of springy. I believe water has found its way
through the flange of the inspection hole into the core, and I believe
that the core has become rotten and has delaminated from the fiberglass
skin. I am going over books to learn the right way to fix this
problem. But I have a question that I don't know the answer.

According to the hull/deck repair books from WEST SYSTEM and Don Casey,
they both recommend using epoxy to glue the new core and the old
fiberglass skin. This makes sense because epoxy is good for attaching
dissimilar materials together. So far so good. Both books recommend
grind down the edges of the fiberglass skin to create tapered edges,
and then put fiberglass cloth and epoxy to link up the old fiberglass
skins together with the fiberglass skin on the deck. I buy the idea of
using epoxy to join the fiberglass skin. But I have a question on how
to finish the surface.

If we use epoxy to join the fiberglass skin, the cured epoxy is the
outer surface before any finishing is put on top of it. According to
Don Casey's book, gelcoat doesn't adhere well with epoxy. He suggested
painting with non-skid additive or attaching non-skid overlay over the
area to cover up the epoxy area. I am under the impression that paint
is not good for high traffic area, right? And I don't know how good a
non-skid overlay will look when it is placed on existing non-skid
surface. I assume that the existing non-skid surface is made from
gelcoat, and I would assume that putting gelcoat with non-skid additive
over that area will be better compatible with the non-skid surface on
the rest of the deck.

Is painting with non-skid additive good enough for high traffic area?

Can we sand the area and then spray a thin layer of gelcoat over the
epoxy and then add non-skid additive onto the gelcoat using a shaker?

What would you do to finish the area?

Thanks in advance for any info.

Jay Chan