Osmosis : what it is and how to treat fiberglass disease
Marine osmosis, this unknown: how to detect and fight it
What is fiberglass hull osmosis?
Keep calm, don’t be afraid: osmosis is not HIV, you can treat and fight it easily. First of all, let’s see what it is, how it forms and therefore what are the possible remedies to treat the sick “stomach” of our “creature”.
All organic substances absorb water and this phenomenon can be slowed down but not removed.
You can verify that if you have a microwave oven, a grandma’s dish, or better, a great-grandma’s dish and a new one. Putting the first and then the second one with a piece of bread in the oven, you will see that, in both cases, bread will be hot but the new dish will be almost cold while the old one will be always hotter proportionally to is oldness.
The microwave acts on aqueous parts and, therefore, the dish, after repeated washings, will keep moisture even after 100 years; all the more so, the hull of a boat. But let’s recover our train of thought.
Gel-coat, the polyester resin used to protect hulls from water, atmospheric and chemical agents and to provide a high-quality finish, acts as a semi-waterproof membrane that activates the osmosis phenomenon: the term comes from the Greek ὠσμός which means “push, impulse “.
Consequently, water passes through the layer of gel-coat very slowly and settles in the interstitial spaces that had inevitably formed during fiberglass processing. Gradually, some bubbles form and increase their volume because they continue to absorb the moisture that slowly infiltrates. Pressure, on the inner side of the gel-coat and in contact with fiberglass, can reach several atmospheres and provoke the typical surface delamination with the formation of a uneven layer commonly referred as “orange peel” that provokes a real explosion as well as the creation of craters whose diameter can range from a few millimeters to some centimeters.
The best way to diagnose marine osmosis is direct observation: you must scrape and remove gel-coat exactly where bulges or balls seem to have formed. If the “disease” is at an advanced stage, visible cavities will immediately appear. In this case, if you put your finger into the small crater and bring it to your nose, you will find a typical smell of ammonia; some spring dads compare it with the piss of a baby stayed long with the same nappy.
Have you seen and smelled? Don’t dispair! There is much to work but, thanks to modern preparations, the result is practically certain: She will recover!
Hull Osmosis Treatment
The operation will start with the removal of protective paints and gel-coat from blisters through (if possible) sandblasting. Then, the surface must be rinsed carefully and more times with fresh water and, if possible, using a high-pressure jet in order to facilitate the cleaning process.
At this point, it is important that the hull dries perfectly, trying to expose the boat in a sunny ventilated area for not less than two months.
When you’re sure that drying is completed, you can give a coat of epoxy primer and plaster craters with a primer-compatible bicomponent preparation, trying to fill every cavity perfectly. Careful sanding will prepare the surface for the application of several coats of high-thickness epoxy bicomponent primer that will guarantee perfect adherence and impermeability.
Only after these steps, in order to conclude the cycle and put your convalescent “creature” in water in total safety, antifouling paint can be applied.
The market offers a dozen of high-quality paint factory brands. Personally, however, I usually choose those that, together with the product, supply a complete and, above all, understandable information material because I think that only those who are able to inform the others exhaustively have clearer ideas on what they produce. Otherwise, how can I transmit you all this science?