Posted by Bengt Blomberg on March 22, 2002 at 16:19:38:
In Reply to: Epoxy osymosis posted by Dennis Kenney on March 21, 2002 at 01:16:06:
: Is epoxy resin subject to osymosis?
Hello again Dennis. Neither polyester nor epoxy are subject to osmosis. That is a stupid old myth only. However, uncured or not properly cured polyester can be hydrolysed. This is due to the fact, that some of the indigredients are made by dehydrolysis or removal of water molecules. Even the last step by forming the long ester chains involve removal of water molecules.
Properly cured polyester will not hydrolyse in itself but most of the binders used in the mats will do so which will cause a 5 to 10 percent loss of structural strength within a few years even in a perfect laminate but the polyester will not be affected.
Unfortunately the only way to obtain a proper curing is to "post cure" the hull for some hours at 80 degrees Celcius. This has so far not been economically possible for a standard boat hull, which is the main reason for the problem.
Regarding epoxy the chemical build and the curing system are totally different and there are no materials involved which can be hydrolysed. One problem here which causes problems is, that the amounts of resin and hardener must have absolutely exact porportions. Any excess of one of them will cause fluid enclosures in the cured material but in this case water will have no influence on them.
Another problem is that some of the amin indigrent in the hardener migrates to the surface during the curing process and forms a thin skin of amin carbonate with the cabon dioxide in the air. If the time span between the layers forming the coating are not properly considered, the next layer will not adhere properly and blisters might form between the layers.
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