You do not need Marine Ply. The difference in Marine ply and normal outdoor
ply, is the marine ply will have no interior voids. All the plys are
patched before bonding. No voids is good in a transom, with a big motor
trying to flex the ply. For normal walking surfaces, a standard ACX with
waterproof glue is fine.
Bill

wrote in message
...
On Sun, 08 Aug 2004 19:57:36 +1000, "K. Smith" wrote:

wrote:
I have a houseboat whose roof has a bunch of thin
spider cracks, as well as some a bit bigger. The
biggest ones aren't wide enough to get any more than
a razor knife blade in, if that. I want to put some more
fiberglass sheet on it, and have never done that before.
Having talked to several people about it, the following
is pretty much the impression I've developed about
doing the job, and I'd appreciate any more suggestions
or advice people are willing to sha

· First, use something like a thin wheel on a grinder and
dig out the larger cracks, then fill them in with rosin to
make them strong...if that's not done before sanding,
the cracks will fill up with dust and never get strength
from rosin entering them.

Resin itself has very little strength so if you choose to fill the
cracks first add some filler to the resin, say Q cells & make a paste
(before you catalyse), although a layer of glass over the top should
mean you don't really need to "fill" suck small cracks first.

Thanks for the input! By now I've changed my plan somewhat.
At this point I intend to fill the cracks with a filler material
recommended
by a guy who does a lot of this stuff, and works at Boater's World. That's
in case water gets between the original roof and what gets added to it,
and also to help hold it over through winter in case I don't get around
to completing the job until spring.

· Sand the area with medium grit sandpaper.

· Clean area with acetone.

That plan has changed too, and now I intend to add 1/4" plywood
for that much extra strength, before doing the fiberglass. That could
change too though... The original plywood idea was to save a bunch
of sanding and acetoning of the original roof, and also add some
strength. Then a couple of people told me that I need to use marine
grade plywood. The expence of fiberglass and resin was significant,
but now the cost of the plywood would become the biggest expence
...more than doubling the cost of the job. So now I'm left to wonder
how much stronger, better, longer lasting would the plywood be to
the project?

· Cut fiberglass cloth to fit the area, then staple in place.

Usually you paint resin onto the surface, then put the glass on, then
use a metal roller to pull the resin up through the glass this stops
bubbles being trapped under the glass (still use staples if you need to
but into the wet glass) & by working the roller with the wet resin you
give the binders in the chopped strand glass mat time to dissolve. So
it's always best to put the resin on first (not too much) then lay the
glass into it.

Thanks. That's pretty much what everyone else has said.

· Saturate the cloth with rosin using a roller. Best to set
up a cover like a tarp, because in direct sun the rosin
could set up too quick.

Always do a test bit to ensure the amount of catalyst you'll be adding
will give you a gel time of 20 to 40 mins, save there's a dramatic
weather change you can then maintain your gel time with confidence.

I've been told to use between 1% and 2%, and also not to use less
than 2%, so still don't know quite how to think about that one. I do
intend to rig a tarp to cover the work area, so the sun doesn't make
things set up too quick.

When
working do small areas at
a time.


· After all that has been done and dries, apply gel coat
...I've heard to apply 1, 2 and 3 coats, so as yet don't
have a good idea of how many to apply.

Just resin with glass sets very porous. The gel coat is what makes it
water tight.

I have had various advice about that one. Most of it has been that
there's
no real need to use gel coat, but that any type of marine paint would work
okay. One guy said he used gel coat, but it was too slippery so he went
over it with Elastomeric....here at this marina most people suggest using
that. The two people I talked to that do a lot of fiberglassing said just
painting
it would do, and both acted like it really doesn't matter what type paint.
One
of those guys did suggest using marine acrylic paint, and adding a bit of
a
sandy substance they sell to give the surface more texture.

With gel coat one good application should be OK, it's
pretty thick stuff but don't skimp, however "normal" gelcoat will leave
a sticky tacky surface, so tell your supplier that you need some "wax in
styrene" to add to it (about 1%) the wax will float to the top & seal
the curing gelcoat from air allowing it to cure right through not
leaving a sticky surface.

Thanks. I'll ask around about that at the supply places.

If it's a tricky surface (doesn't sound like
it) you can spray some PVA over normal freshly applied gel coat to
achieve the same outcome.


One of the things I'm still trying to figure out, is how to
deal with the excess rosin which will want to drip down
the side of the boat. Can anyone suggest any good way(s)
of dealing with that issue?


Masking tape & throw away placky drip sheets from a paint shop etc. If
you have a situation which doesn't allow, you can spray PVA over the
lower surfaces (it's cheap mould release agent which sets quickly into a
placky film) then when finished the drips etc will come away easily, the
PVA is water soluble so can just be harmlessly washed off.

K