BoatBanter.com - Epoxy or Polyester for Fixing Rotten Core on Deck?

Terry Spragg wrote:
wrote:

Terry Spragg wrote:

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

I put the original top deck pieces back, using epoxy goo and
adjustable height guide screws under the top bits, into the new
core. Wipe of the excess with plasic baggies, possibly to re-use and
then with dampened acetone rags, pressing gently, and weight down
lightly to cure with poly bags of dirt. The poly doesn't stick.

Clean up the pattern with a spoon, then when hard, a dremel, and you
stand a chance of never noticing the scars, if you cut it off
sensibly with a thin dremel cutter wheel.

Spring will tell if, instead of whittling for a week, I should have
put down an overlay of glass, resin, poly plastic sheet, and
expanded metal grille to form antiskid. It's been two years now, and
I am not afraid to do the stbd side, in about 10 more, the same way.

Terry K

I am trying to understand what you are saying.

What do you mean by using "adjustable height guide screws under the top
bits, into the new core"? Do you mean using screws (and epoxy) to
attach the old fiberglass skin to the new core? Then you need to deal
with covering up the screw heads, right? What's the purpose of using
screws? Should we simply use epoxy alone instead?

After the replacement core is in and cured, the top deck removed
earlier is used to close the deck up again. Levelling the top is
accomplished by putting screws down into the new core at the corners
of the removed pieces and adjusting them so the top piece ends up
resting level with the unaffected deck. Once the adjustments are
made, an ample gob of goo is used to stick the top piece back where
it belongs, covering up the height adjustment screws, and squeezing
out the excess very gently to avoid sucking air back under the top
pieces when heavy pressure is released. The excess is removed,
wiped off with plastic bags, leaving the original surface more or
less flush, with thin lines of epoxy, scars, sealing the saw cuts
used to remove the top sections.

When you said "Clean up the pattern with a spoon", I assume you mean
using a spoon to remove the excess epoxy that gets sequeezed out from
the joint, right?

Right.

What you said "..., a dremel, and you stand a chance of never noticing
the scars, if you cut it

(the top pieces)-tk

off sensibly with a thin dremel cutter wheel",
I assume you mean using a small Dremel power tool to cut out the excess
epoxy that gets sequeezed out from the joints and has become hardened.

That, too. I also used a small wire brush and a grinding wheel to
sculpt the joins in the anti skid surface, restoring the appearance
considerably. I did not tint the goo used, as it would need a lot of
pigment, would likely not match colour, and the deck would still
want painting.

I used a dremel thin cutting wheel to excise the portions of deck
under which I suspected the core was rotton, then pryed up the
sections removed. The pieces were about a foot square at the
largest. In some areas, the rot was not as expansive as the section
cut out, and this presented an obstacle to lifting the top deck
piece free. A special saw was made from a folding Coughlin camp
saw, by filing a few extra teeth in the end, and with it, I was able
to saw through remaining good core to release the top section where
the core was still good. I was afraid of breaking the top sections
being removed where it was stuck down to good core parts.

It was neccessasry to scrape out under the unremoved sections 3
inches in some cases where I was close to the boundary of good and
rotton core. I did not remove the entire side deck in one piece, as
only about 1/2 of it was bad, mainly along the gunnel, almost where
you could envision water channelled by gravity.

The replacement core was not tightly fitted, was mainly there to
reduce the amount of epoxy goo used to build up the core section.
So, the new deck is as much epoxy as it is replacement core. I guess
the boat is about 1o pounds heavier than it was, excluding the
absorbed water in the blck mush rotton core.

I used a large syringe made from an old caulking tube to inject
thickened epoxy goo into the areas where new core was fitted under
the deck where I had scraped out bad core.

A friend who does this commercially says that among other custom
tools he uses an ice chipper sharpened into a chisel to cut through
large areas of remaining good core, to enable lifting larger
sections, cutting only along anti skid edges to preserve the
appearance of the deck. He said it was a lot of work to get entire
sections cut out whole that way. I feared my underdeck glass was too
light to support much prying pressure and was right. It was only a
very light scrim under the core. Remember, moulded boats are applied
to the female mould from the outside layer gelcoat first, then layer
by layer through to the interior.

Solid epoxy 5/8" inches thick has got to be stronger than balsa wood
core, if not as light or cheap to manufacture. I have jumped up and
down on the new deck, and trust it enough to "bury the rail," or
sail hard.

I don't understand when you said:

"Spring will tell if, instead of whittling for a week,
I should have put down an overlay of glass, resin,
poly plastic sheet, and expanded metal grille to
form antiskid.

[new paragraph] -tk

It's been two years now, and I am
not afraid to do the stbd side, in about 10 more,
the same way."

I have a feeling that you are trying to say that your method should be
as good as another method, and the other method would take more steps
to get done.

I was referring to another method of restoration of the antiskid
pattern which would possibly give a better finish appearance.

What I don't understand is that if you had already done
the repair ten years ago, you should have known the result by now. I
am wondering why you still need to wait for next spring to know the
result.

Jay Chan

I did port side deck two years ago. I am happy enough with it.

The stbd side may need doing in a few (pray it takes ten) years, as
it is a little suspicious, but not obvious. If I do it, I will do
it the same way, especially since the stbd side is obstructed
underneath by cabinetry, etc.

Spring will reprove the durability of the repair. Early this spring
I was delighted to see no evidence of cracks or other new damage.
Around here, freezing -30 celcius winter ice will expose weaknesses
in waterproofing dramatically. This rot spreads by virtue of
expanded ice in damp core seperating the bond in it's niegbours, an
inch at a time over the years, to enable water to spread within the
core, freeze, and perpetuate the process, year by year.

Terry K

Thanks for explaining to me. You have brought up some issues that I
didn't think of previously.

I didn't realize that we need to level the removed fiberglass skin when
we try to glue it back in place over the new core. I thought it would
simply lay flat on its own. Does this have something to do with the
possibility that the fiberglass skin may have been deformed by the
flexing of the deck and by the process of removing it from the damaged
core? I will need to pay attention to this issue when I need to put
the fiberglass skin back in place. Thanks for pointing this out.

Seem like you used a dremel cutter wheel to make a thin cut on the deck
to remove the fiberglass skin, and then later on you used epoxy to join
the removed fiberglass skin with the unremoved fiberglass skin. I have
to wonder how strong the connection is. This cannot be as strong as
using fiberglass cloth and epoxy to join the two edges together. I
have a feeling that your method is probably "OK" if the area is very
small; but this will not be the method that I will use. I think I will
stick with the "taper the two edges and epoxy them together with
fiberglass cloth" approach.

Thanks for pointing out that the inner fiberglass skin is quite thin.
I will watch out for this when I need to remove the damaged core. I
surely don't want to break the inner skin, and make the repair more
difficult than necessary.

I see your point of preferring solid fiberglass deck instead of cored
deck. But I will have to stick with using core material in order to
match the area surrounding the damaged area. Thanks anyway.

Jay Chan