Hulls made of polyester or fibre glass started to appear in the middle of the 1960s. These new materials were an instant success. Polyester reinforced with fibre glass has become the preferred material for building pleasure boats.
After several years in the water, these polyester hulls – if they are not properly maintained – have, however, revealed their weakness against humidity.
This phenomenon of degradation is called osmosis.
Polyester and Fibre Glass Boats in Focus
Even if you can still navigate with a boat that shows signs of osmosis, it is still recommended to solve this problem.
What is osmosis?
To say it in a few words, osmosis is quite simply letting water penetrate into the polyester material.
Osmosis is the result of a disbalance between two fluids with different concentration, which are separated by a semi-permeable membrane (the gelcoat).
The liquid with less concentration (water) goes through the membrane to rejoin the liquid with a higher concentration (the solvent), thus creating a chemical reaction that is called hydrolysis.
Which impact has osmosis?
The encounter between solvent and water produces blisters that contain acetic acid. The acetic acid can be easily identified by its strong smell of vinegar (if you pierce a blister).
Please note: In sweet water, osmosis shows a much faster progress than in salt water and is therefore of increased importance.
What should I do if there is osmosis?
To get rid of osmosis on a boat, a “peeling” should be made. This measure means sanding down the hull – the gelcoat is removed so that the hull is uncovered.
Should there be a lot of osmosis, it is also recommended to sandblast the hull to eliminate all blisters in greater depth.
After the hull has been carefully rinsed it must be dried completely so that it can absorb the gelcoat and the preventive treatment.
Being a true protective barrier, this treatment makes the hull water-proof because of the epoxy resin contained in it.
After that, a coat of paint called antifouling can be applied to prevent that aquatic organisms will settle again on the hull of the boat.
Osmosis is a very common phenomenon on old boats that were built when the methods of stratification and the application of gelcoat were not yet state of the art.
On boats built in the recent years, the phenomenon of osmosis has been considerably reduced.
If a boat suffers from osmosis, its structure will be weakened. Therefore it is advised to limit this development by treating it as soon as it manifests itself on the hull.