[Public-list] Kevlar

[J Bergquist]

Roger-

It depends more on the resin than on the cloth. Kevlar is usually laminated
with either vinylester or epoxy because polyester does not work very well
with Kevlar. Epoxy is the best of the three in terms of material properties
(waterproofness, elasticity modulus, and stickiness or 'quality of bond').
It's also the most expensive. Vinylester is in-between, and polyester is the
low end.

Epoxy will stick to any of the other resins, if the surface is properly
prepared.

Not everything will stick to epoxy, though.

Therefore, your safest bet is to use epoxy. The advantage is that you can be
pretty sure it will work just fine. It also is 100% solids so does not
shrink, whereas styrenated resins (polyester and vinylester) will shrink
because they give up styrene to the atmosphere. This can be an issue when
you are using polyester as a resin when adding on to a pre-existing part
(the new resin shrinks while the old part won't). This is a bigger issue in
bigger parts so for a small part like you are talking probably not too much
of a problem.

The downside of epoxy is that it's more expensive and more difficult to use
than either polyester or vinylester. You have to mix it in very careful
proportions but with modern systems this is not as much an issue as it used
to be because they are pretty idiotproof, using pumps to dispense precise
quantities.

I like to use West System, but it is more expensive than MAS, Barrier, or
System3, which are other brands. I have never had a batch of west system not
cure on me. I have had problems with Barrier. I have little or no experience
with MAS or System3. There are lots of other brands too. I feel that you get
what you pay for. If it doesn't kick, it's a gooey mess that is a pain to
clean up and a waste of time, so I feel that, particularly for a small job,
get the good stuff is good economy.

Material properties are probably not really an issue for your application
and I guess cost probably is not really that big a deal either because you
are not going to use much of the stuff.

One thing to be concerned about when preparing a kevlar surface is that it
does not sand well. Kevlar is a very 'tough' fiber and basically if you try
to sand it all you do is make it fuzzy. It does not sand like glass at all.
So be aware of that and don't sand through the resin if you can avoid it.

Also, you can probably make your flotation tanks out of glass. It's cheaper,
easier to work with, and for this application stiffness is probably not an
issue. You just want watertight integrity. You probably will not save very
much weight using Kevlar over using glass.

Good Luck,

J Bergquist

On 11/1/06, Roger L. Kingsland <r.kingsland at ksba.com> wrote:
>
> This is a non-Alberg 30 question but I figure someone in this a gust group
> must know the answer.  I recently bought a 16 foot "polling boat" made of
> Kevlar.  I would like to expand the built-in flotation compartments at each
> end and don't know if standard fiberglass tape and epoxy will stick to
> Kevlar or if I need some other stuff.  Any thoughts?
>
> Thanks, Roger
> _______________________________________________
> These businesses support your Association:
> http://www.alberg30.org/store/A30supporters.html
> Please support them.
> _______________________________________________
> Public-list mailing list
> Public-list at alberg30.org
> http://alberg30.org/mailman/listinfo/public-list
>

 1162411046.0