On Sat, 08 Nov 2014 15:45:53 -0600, Richard
wrote:

On 11/8/2014 12:16 PM, Ed Huntress wrote:
On Sat, 08 Nov 2014 11:34:48 -0600,
wrote:

On 11/7/2014 12:08 PM, Ian Malcolm wrote:
wrote in news:Ydqdncz1e6oLZ8HJnZ2dnUU7-
:
Not at all.
But you COULD say that gelcoat is nothing but laminating resin with WAX
added...

No. Commercial gelcoat does *NOT* contain wax as it would impair the bond
to the laminating resin in the layup being applied to the gelcoat in the
mold. Flocoat contains wax for a non-tacky surface cure. Some entry
level gelcoat repair kits contain wax, but if you are serious, you either
seal polythene sheet over the repair to exclude air or use wax in styrene
additive.


Ok, I guess I'll retract that.

The stuff I use does have wax so that it is self sealing, but I take the
point...

The stuff you have likely is made for applying *after* a part is
pulled from a mold, on the outside of the laminate.. You need the wax
for that, or the surface could stay tacky forever. As Ian says, there
are better ways to block the air from the gelcoat, but most external
application is repair work, and, at Ranger, we added wax (or our
repair specialist did) for making patches.

Gelcoat sprayed in a mold, where it's covered with layers of glass and
resin, doesn't need it -- and is much better off without it.

The gelcoat-to-laminate bond is the most critical one, and needs the
strongest bond. Since I have a few minutesg let me try to add to
this discussion.

Polyester resin is a very poor adhesive. If you lay one layer of cloth
or woven roving (which is very coarse cloth) on top of another, the
peel strength and shear strength are very poor. The same is true if
you lay any fiberglass, including random-oriented mat, on top of
already-sured resin or even gelled, but not cured resin. That's what
happens when you lay the first layer of mat (or veil -- see below) on
top of the gelcoat in a mold. It has to be firmly gelled before you do
that or you'll poke through the gelcoat. And the result of letting the
gelcoat partially gel before continuing the laminating is that you
need all the help you can get to stick it to the next layer of
laminate -- no wax, please.

Now, about the interlayer strength of the laminate. Again, adhesive
strength of polyester resin is very poor. Cloth-to-cloth layers often
can be peeled apart by hand. The highest quality laminates, as in
expensive racing dinghies, use a minimum of mat because mat layers are
weak. But those boats, like all other expertly done polyester
laminates, must use mat between layers of cloth. Or they use veil,
also called "scrim," which is a very thin, semi-transparent layer of
mat. You get the best strength-to-weight, and stiffness-to-weight,
using veil and fairly light layers of cloth. (you can look up E-glass
versus S-glass to get more detail on making the best polyester
laminates.)

When the resin, or the styrene monomer in the resin, dissolves the
binder that holds dry mat together, the fibers get loose and tend to
"cog" their way into the layers of cloth above and below as the layers
are brushed out, and poked with the brush, or rolled out with a disk
roller. This assumes that all layers are still wet.

That's where the interlayer strength comes from. Polyester is a lousy
adhesive but it has decent bulk strength, in a laminate, at least, and
it holds those cogged pieces of mat into an interlocked mass with the
cloth. (The cloth is inherently stronger because of the long-fiber
orientation, not really because the fibers are just longer.) That
overcomes the lack of peel strength and sheer strength in the resin.
Unfortunately, you can't achieve the high glass-to-resin ratios with
mat that you can with cloth, so the mat parts of a laminate are
inherently weaker and a lot less flexible. Any boat that uses more
than a minimum necessary amount of mat is less strong -- but cheaper
to build.

About wax: The best deal is to use resin without wax until you get to
the last layer, the one that will be cured while exposed to air. But
the wax dissolves in the resin, and, if you lay one layer of waxed
resin on rop of another, most of the wax will dissolve again and rise
to the top. How much, I don't know, but I know that many boats have
been made with waxed resin in each layer of laminate, and I've never
heard of it causing a delaminating problem by itself. Maybe it does;
perhaps Ian knows.

One final thing: None of this applies to epoxy laminates. Epoxy has
such strong adhesive properties that you can laminate one layer of
cloth on top of another. Epoxy laminates are a lot stronger to begin
with. Avoiding the use of mat makes them even stronger.

Watch out, though, that your glass cloth, or mat if you use any with
epoxy, are made for use with epoxy. The finish on glass cloth made for
polyester is actually weaker than a straight glass-to-epoxy bond.
Don't use it.

As for mat, the binder won't dissolve in epoxy. Try it, and you're
likely to get a real mess. (this is the voice of sad experience --
before I learned about this). But you shouldn't be using mat with
epoxy in the first place. Epoxy make a much stronger laminate without
it.

Phwew.g


Preaching to the choir, Ed. I'm an epoxy guy.
I've used polyester in the (far) past, but gave it up as soon as I
found the light.

My first love was Dow 330, but it's not made any more.
It was fairly benign stuff as toxic chemicals go, but would crystallize
at cool temps. One only had to warm it up to be usable again, but that
was too much hassle for too many users.

These days it's mostly West 105, unless there is a physical requirement
that is beyond what that stuff can provide.

Strictly volan coated woven glass for me.

I use both for small projects, depending on what is needed. I made
some giant clams out of polyester and mat, with a thin cloth coating,
for my wife's classroom presentation about the deep sea. I figured
they'd last long enough. g

I'm a fan of the WEST System, but I usually use System Three. It is,
or was, a lot less expensive. I've had good results with both.

BTW, speaking of the WEST System, I've sailed with the Gougeon
brothers, on Adazio, when all three were young.

http://www.westsystem.com/ss/old-lad...-70-mph-blast/

--
Ed Huntress