OSMOSIS Check
With the introduction of higher quality isophthalic and vinyl ester resins in the production of GRP boats, osmosis damage to newer boat models has become less common. Nevertheless the risk is still a concern for many owners or potential buyers of used boats.
A careful and recurring inspection of the hull as part of a survey can reveal weak points in the osmosis protection of a hull and thus avoid expensive renovation cases in good time. For this purpose, we use high-quality moisture measuring devices, specifically designed for FRP testing, as well as active thermal imaging technics in case of suspected Osmoses presence.
My experience has shown that early treatment of blistering tends to be less successful than treatment of vessels with more advanced problems. While this may seem to contradict normal precautionary practice, it has been found that breakdown reactions in GRP laminates take some time to reach their conclusion; and if treatment is carried out prematurely it is much more difficult to remove reactive or hygroscopic compounds from the laminate, with the result that a recurrence of the blistering is much more likely to occur. The overriding factor must always be the integrity and safety of the hull. Osmosis in its early stages is very much a chemical condition, which has very little effect on hull strength.
Yes, blisters are unsightly and may cause a resale problem. These are all factors you must weigh, in addition to the very high cost, when deciding to repair or not. Further, you should also be aware that the number of failed blister repair jobs that I find is very high. No one's ever going to know why blister repairs fail because no one is going to spend the money to find out. That there are so many should also play a role in your decision to repair or not. And even though the repairer may give a warranty on the repairs, you should get it in writing and read the fine print. Then make sure the repairer is likely to be around years later to honour that warranty if it becomes necessary.
If the blisters are large and numerous, it would be wise to seek unbiased, professional advice before you proceed. Bear in mind that blister repair jobs are now big business for boat yards, so taking advice from yard managers may not be a good idea!
Moisture meters measure only the surface moisture, and since gel coat and paint is very porous, the moisture meter is only going to tell you what you already know; it's wet. It cannot tell you anything about the propensity of a hull to blister. While these instruments have their uses, predicting whether a hull is prone to blistering is not one of them.
All things being equal, you would certainly want to choose a boat without blisters. Unfortunately, unless the seller is kind enough to tell you, you can't find out until the boat is hauled out for survey, at which point you've already invested some money in it. It's a fact that most blistered boats are sold without regard to the blistering, and this is one of the reasons why, in my experience, the number of cases where blisters cause the boat to be rejected, or give rise to price renegotiations is considerably less than 5%.
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