Posted by Bengt Blomberg on August 01, 2001 at 17:45:08:
As I have mentioned many times, the polyester laminate is an absorbing material. Submerged in water it will always absorb a certain amount of water, normally ranging between 0,5 and as much as 10% depending on age and quality. In addition to this, the buoyance pressure will cause small amounts of moisture to pass right through and evaporate on the inside. An epoxy shield ABSORBS much less water than the polyester. Sometimes as much as 20 times less. This has been used by paint manufactures to make people believe that it also stops water from PASSING THROUGH when the pressure is higher on one side than on the other.
In fact there is no material that can be applied and dries or cures in normal temperatures which can prevent water penetrating and the submerged laminate will always contain sufficient moisture to feed a hydrolysis of the polyester if the criterias described in this web site exists.
On the other hand, if those criterias do not exist, the laminate can contain 10% moisture for decades without any hydrolysis problems.
The high moisture readings on an "osmosis" hull are the result from water entering into the cavities caused by the hydrolysis and not the opposite.
Hundreds of comparing tests I have performed show, that if the actual reasons for the hydrolysis are not removed or neutralized before a "protective" coating is appled, the damages become worse in most cases.
Some manufacturers claims, that their resins are more effective because the addition of flakes of high molecular impermeable hard epoxy or silica based materials. It is true, that this causes the water to have a longer way through the coat but it is the same as having two garden hoses of different length: When the tap is turned on, the water will need more time before coming out of the long hose but after that there will be no difference in the amount of water they deliver. In our laminate case, the flakes will not keep the amounts needed for a hydrolysis out for more than a few weeks.
In my humble opinion a "protective" coat is a waste of money only.
Today there is another possibility available for those who wants to protect their new hulls from future "osmosis": The HotVac post cure treatment which can be performed at reasonable cost in a few days time. The distribution has just started but it will not be long before most markets are covered. Ask your boat yard to check their web site. There is a push button link on the osmosisinfo.com preweiw page.
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