This will be much easier if you just remove the upper surface (gelcoat)
from an area larger than is damaged, thoroughly clean out the damaged
core, recore, and replace the gelcoat. Your repair will look better if
you make your cuts along areas where there is no nonskid pattern, as its
a lot easier to produce a smooth surface to conceal the cut than to try
to replicate a pattern.

For areas where you have hardware going through the deck, I would
suggest making a solid deck a bit larger than the hole, then redrilling
the hole. I suggest this in the belief that caulking will fail, and
some water will eventually get into the hole, so you want to have a
barrier around the hole to prevent the water from getting to the core.
This is fairly easy to do by blocking the hole from below (taping a
scrap of wood over it, for example), removing the new core in a circle
perhaps an inch around the hole, and filling this area with epoxy as
high as the core and being sure there is a little epoxy there when you
replace the gelcoat, so there is sealing. This is more work than most
manufacturers are willing to do.

To prevent this problem from developing in other areas, remove the
hardware, then remove some coring around the hole (a bent nail in a
drill works well for this), then block the hole from below with a taped
scrap of wood, and pour epoxy into the hole as high as the top of the
gelcoat. When all has set, redrill the hole.

When I was young my father had a wooden boat. I vowed to always buy
fiberglass as there would be far less maintenance. I was wrong.

Michiel wrote:
Hello,

I'm looking for a little bit of advise. This is more boat repair then
boat building, but I'm figuring you guys here would have the right
kind of knowledge.

At the beginning of the summer I bought a trailerable fiberglass
minicruiser (a 1983 Gloucester 20). When it rained in the fall I found
there were some leaks into the interior and I found out that the
central part of the deck (not all of it) is balsa cored and one side
of this is saturated with water. All of it has some delamination.

I drilled some holes from the inside and found that the port side is
wet and some of the balsa is dark and the starboard side is mostly
dry. The water may have come in at holes for deck hardware and some
cracks in the gelcoat, one of them spiderweb shaped. As an extra piece
of information, the mast rests on a higher area of the deck which
seems to have a thicker core (probably not balsa) which is dry.

I want to stop the water from getting in and I'm also concerned that
the delamination will cause the gelcoat to flex more and thus crack
more. It's been on my mind and I've thought of the following options:

1 - leave it be. put deck hardware back on sealing carefully with
polysulfide or 3M 4200. Perhaps drill a large number of holes in the
inner skin so the balsa can dry out.

2 - cut out inner skin, scrape out old balsa core and glue down new
balsa or plastic core and then cover this with polyester and
fiberglass.

3 - cut out inner skin, scape out old core and add multiple layers of
fiberglass and polyester, building up until the deck is nice and
stiff.

I'm strongly leaning toward option 3, but also considering 1.

Let me know what you think, please!


Thank you,

Michiel van Wessem