OzOne wrote:

On Wed, 30 Jun 2004 15:35:01 +1000, OzOne scribbled thusly:

Actually Nav, without the osmotic pressure there would probably NOT be
blistering below the waterline.
Water would still penetrate the gelcoat, react with the chemicals in
the resins and provide the circumstances for osmosis, but if the
pressure didn't exist then thers wouldn't be enough force built up to
produce the blister.


Oz1...of the 3 twins.

I welcome you to crackerbox palace,We've been expecting you.


Then again, does the initial reaction of the water with the agents in
the resin produce enough gas or other force to initiate a
blister.....I don't know.
Do you?



This question was solved in 1990's I think. Only three factors are
needed, unpolymerised monomers, water and a void. If the void is not
spherical (i.e. dry glass fibers) the blister risk is greater. All
resins contain about 5% free monomers etc. These dissolve in the water
(all resisn are water permeable to some extent) and I estimate that at
25% solute in water within the polymer void that the osmotic pressure
could be about 100 psi. This pressure then starts delamination due to
the law of Laplace and the limited tensile (adhesions) strength of the
polmer. The resin (or gel layer) then start to peel from the glass
fibers and grows rapidly from then on... The process is worsened by the
leaching of resin by the water too.

Cheers