Re: [Paddlewise] gelcoat vs resin??

Bob Wrote;

-

>So what's the difference between gelcote and resin especially in
>regards to repairs of cracks and other minor tasks.

Gel coats are usually (but not always) more flexible resins that will
absorb more impact without cracking. The are usually sprayed to a thickness
of 10 to 15 mils without any fiber reinforcement.

The gel coat resin is modified by adding UV stabilisers (rarely used in
laminating resins), thixotropic materials to keep it from running when it
is applied in the mold, pigments, fillers, and other additives to obtain
specific characteristics. It is a bit of a witch's brew of materials.

Because of the fillers etch. gel coats are not good for laminating. They
don't impregnate the fiber fully and lack adhesion. Because they lack the
fillers etc.. laminating resins are not good for surface coatings.

Both materials have a specific job to do and it is best to use them for the
purpose they were intended. I.e. use gel coats on the surface and resins
for laminating.

Some boats are built by adding pigment or pigmented resins the laminating
resin. This reduces weight at some loss of visual appeal as the fiber often
shows through at the surface. For boats that are continuously in the water
this is a bad practice as water will wick into the fibers and reduce
strength an cause blistering. gel coat (and other surface treatments) help
resist this permeation by water. On sea kayaks I don't feel this is a
problem because the boats don't stay in the water permanently and my own
boats have all been built without the gel coat layer with no problems
appearing. The flip side, as mentioned earlier, is that they aren't as
pretty because the color isn't uniform and the fiber pattern shows through.
I would be concerned if the boats were stored outside and exposed t the sun
al the time for then the small amount of pigment and fillers in the mix
might not provide adequate protection and a loss of strength will occur.
Some manufacturers laminate boats with clear gel coats and my conversations
with rental operations is that this reduces the life of the boat. I have
seen one Kevlar boat that I could push my finger straight through the
laminate. While the manufacturer would not admit it I suspect the resin and
gel coat used lacked UV stabilisers as I have not seen other boats that
were quite that bad.






***************************************************************************
PaddleWise Paddling Mailing List
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.gasp-seakayak.net/paddlewise/
***************************************************************************