What is osmosis?
The word osmosis used to strike sheer dread amongst boat owners, particularly when lengthy articles were published in the yachting press. There was a period in the late 70’s when simply the word ‘osmosis’ would send prospective purchasers into blind panic, surveyors were so cautious they would not stand by a boat that was blistered and osmotic treatment centres sprang up across the country rubbing their hands with glee. This is a brokers observation of having sold boats before the condition occurred and now that the situation is much more professionally controlled. During that time boats have come and gone, provided very good service and only in very, very extreme cases required any remedial work. When GRP became the industry standard for boat production we breathed a sigh of relief, no more rotting wood or rusting steel to deal with and to a great extent this tranquillity prevails today.
To some extent all fiberglass hulls, when immersed, absorb moisture as no gel finish is totally waterproof, even the most impervious surfaces such as epoxy paints can absorb moisture. Once moisture ingresses into the laminate it will mix with the chemicals in the GRP, mainly styrene. This creates a solvent solution which in time will create hydraulic pressure within the laminate which will lead to gel coat blistering though this phenomenon is rare in the structural laminate. When a blister is punctured the fluid will have a pungent smell.