Gel Coat vs. Water

When Fiberglass boats were first made, the gel coat (outer skin) of the hull was believed to be an layer that would keep the underlying resin and fibers dry forever. We now know that some boats can and do develop blistering and delamination on and in their hulls caused by water getting inside this gel coat layer.
It is within these layers of cloth, matting and resin that the trouble starts when the water seeps in through the gel coat.
As small amounts of water get inside, it begins to dissolve the chemicals found there. This gooey solution then attracts even more water through a process called osmosis. Then, when enough water has accumulated in this area it creates a blister which eventually delaminates more of the surrounding area, making room for even more water. If left unattended, this process can and will destroy the structural integrity of the hull.
There are three (3) basic types of plastic resin used in boat construction.
(1) Polyester Resin – the least expensive and most porous (allowing the most water seepage / absorption) of the three.
(2) Vinylester Resin – more expensive, but much more resistant to water penetration / absorption.
(3) Epoxy Resin – the most expensive, but extremely resistant to water seepage.
Vacuum bagging is a process which is used in some hull construction. This process applies a tremendous amount of air pressure to force resin penetration throughout all of the matting and / or coring material. This process also ensures there will be no dry spots or excessive puddles of resin laying about.
Many new boats come with a 5 or 10-year blister warranty. These boats have already had an epoxy barrier coat applied at the factory. However, if you sand this coat or hit something that destroys the integrity of the barrier coat, then the warranty is void.
If your boat already has blisters, or is starting to delaminate in places, it is time to fix it.