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Osmosis involves many boats, including those apparently healthy. Our marine expert make the point on what is usually called " the fiberglass cancer", taking down common senses and incorrectness, often used for business interests
BEWARE OF BLISTERS
So here, in a nutshell and few sentences, is what you might hear at the waterfront on osmosis:
And here I stop before I loose completely my temper instead of making my point on osmosis, in a clear and practical way so that difficulties and problems of this fiberglass' disease (which is not a cancer but a measles and on which I already wrote some years ago on Nautica) are identified . In reality, it is very expensive measles, which can be definitely cured by applying, more than technology, honesty only as we shall see later. However, let me please give a brief history on fiberglass.
It is clear that this enthusiastic description is, still today, in everybody's mind and fiberglass is regarded as a long lasting, inexpensive and low maintenance material. Small fiberglass crafts production started in Italy at the onset of the sixties. With a LOA of 2.5/5.0 meters these open boats were not easy to sell since wood was still the most popular boat building material.
But within few years things changed for the better for fiberglass which seemed to be a problem free material versus wood, was inherently adaptable to the industry demands and required a relatively limited trained workforce.
The "whys and hows" osmosis appears have nowadays been fully answered and the phenomenon should be a thing of the past; yet I am still here arguing and yelling, facing a ridiculous situation. how it can be that in 1996 there are still people who does not know what osmosis is and how to go about it? This is the unfortunate reality and my only hope rests on the belief that misinformation and not dishonesty belies it. I will then try to illustrate and discuss issues regarding osmosis in a clear and comprehensive way so that users, as well as professionals who, for various reasons have treated the problem as either non existent or, worst, unavoidable and impossible to cure.
WHAT IS OSMOSIS AND HOW IT LOOKS LIKEIt is a chemical-physical phenomenon, happening during the migration of a solvent, in this case water, through a film separating two liquids with different salinity concentration. This does not really mean a lot, without understanding what really happen in a water immersed fiberglass hull.
The phenomenon will go on as long as the hull is in the water; the blister that at the beginning nay measure 3 to 4 millimeters in width will increase, due to the inside osmotic pressure, with time and permanence in the water. In other words, once started, the osmotic process will continue without any possibility to appraise beforehand the speed at which it expands.
It can then be said that osmosis is a degenerative disease which does not stops by itself unless the hull is kept out of the water; even then, and after months of being sheltered, the liquid may be present in the laminate and, due to the fiberglass' permeability, it will move along the fibers. This is why, after a wile, bubbles appear smaller due to reabsorption.
This proceeding characteristic can be "smartly" put to use when selling a boat with osmosis: it is in fact sufficient to keep the boat ashore and sheltered for some time until the blisters are smothered because the liquid inside them has now spread over a larger area and, also, because the antifouling coating has become uneven thus hiding blisters and others defects.
The only way therefore to see if a boat, ashore for some time has osmosis, is to check the hull's humidity with an hygrometer and taking samples of antifouling coats. Care and caution must be exercised during these tests since humidity alone may not mean osmosis: for this to be present, bubbles must be liquid filled, as we shall see later on.
At this point I hope not to have confused the issue too much: all I want to say is that gel-coat osmosis blisters will definitively be liquid filled while humidity absorbed by a hull is not an osmosis generated symptom.
What kind of bubbles will surely indicate osmosis?
Is there a relationship between blisters diameter and osmosis' age? Yes it does and it means that a 3-4 millimeters bubble with a bright liquid indicates a very recent osmosis; while a 3-4 centimeters pertain to an old one containing dark, strong smelling liquid and an inside high pressure.
Osmosis age is important, a Marine Surveyor is often called to pass opinions on a second hand boat, either to settle a claim or on other related issues and he must be able to state if found defects are recent and not discovered by the owner or, if it is years old and should have been identified by the same owner. All these issues are of a very delicate nature and usually surface in Court when a boat was bought without a dry hull inspection and osmotic blisters could not be seen: in a situation like this the previous owner will obviously declare that osmosis was not present when he owned the boat; in the same fashion, the buyer will try to demonstrate that osmosis was already some years old and the seller should have been aware of its presence.
In short, for a blister to be of osmotic nature, it must have a round shape, it must be located under the gel-coat or similar surface and it has to contain an oily liquid with an acetic smell.
WHY DOES OSMOSIS OCCUR?
There is however a case when osmosis does not happen even if water absorption occur. If the gel-coat surface shows blisters not rounded but elliptical in shape (narrow and long) and pointing in different directions, most likely we are facing only a minor laminate water absorption instead of a n osmotic phenomenon. It usually involves only the first mat layer and the water does not solve any substances. It is also true to say that this is a fearly rare case, mainly noticeable on older boat were lamination has been done in a very accurate way and according the rules, but where with time the gel-coat has weakened and has allowed some water penetration, without generating osmosis.
Here it is why an accurate survey is a must before concluding that blisters are of osmotic nature.
As mentioned before, water absorption by itself creates small oblong bubbles, fairly noticeable as soon as the boat comes out of the water; if on the other side the hull has been ashore from some time it could be that the previously absorbed water pours out of the laminate, which could be found almost dry after the hygrometer test. In this case the blister could result in a dry cavity and this is one more reason to be careful osmosis diagnosis.
OSMOSIS SEVERITYLet's state it clear: a hull either has or has not osmosis.
Then if it has it, its age will not effect the approach and curing methods. It does not make any sense to minimize osmosis presence simply because it is recent, and an older phenomenon will not change the curing method. Young osmosis that has not involved a large surface could allow a 2-3 months period before repairing it; if it is spread on a relatively wide surface with wide diameters blisters, it will be convenient to act as soon as possible.
This concept is widely accepted and confirmed by the fact that Italian Classification Society (RINA) Surveyors, when inspecting hull for osmosis, may grant some limited time exemptions instead of requiring immediate repairs.
But what is the meaning of light, young and heavy, older osmosis?
If blisters are small in diameter and concentrate on a definite hull area not completely affected, we can say that this is young osmosis; if on the other hand blisters are spread most of the hull surface are of large diameter with dark pressurized liquid inside, we can say that we are in presence of old and severe advanced stage osmosis.
Let's remember that a neglected young osmosis quickly switch to an advanced, more and more severe stage.
Why is it more severe? What happen inside osmotic blister if not cured?
It is usually said that osmosis is a degenerative process because, if neglected, it becomes worst and worst: in fact, a blister if constantly kept under water will act as a never ending suction pump continuously widening the blister's diameter. The osmotic pressure thus created, will force the inside liquid to expand not only towards the periphery but also towards the inside of the laminate.
If the liquid will find an effective protection on a resin rich ply, the blister will only grow in peripheral dimensions; if on the other hand, the liquid will find voids in the laminate thickness, the latter will absorb more and more water.
In most cases osmosis remain a superficial problem: if caught at its first stage, it will often involve only the first ply after the gel-coat. If neglected, it will assault the deeper plies. It will then be noticed that a large blister not only create a circular delamination but tend to spread inside: something to avoid as curing takes longer time, is more expensive and more difficult.