Osmosis is a result to water vapour and humidity transmission through the gelcoat layer, affecting the fibreglass laminate and its strength.

The gelcoat is not a totally waterproof barrier, so humidity will penetrate through it. Other factors that contribute to the development of osmosis, are water and moisture in the bilges.

In both cases water will react with non-reacted chemicals entrapped in the fibreglass laminate due to wrong curing conditions or speed during production of the hull. This reaction creates different pressure between the internal liquid and the external sea water, and the osmosis starts. The fibreglass will continuously absorb moisture, and this will damage the structural strength seriously.

It is not always easy to detect osmosis, but blisters may be an indication:

 

• Blisters (usually of different sizes) filled with liquid of brown colour and with a vinegar odour indicate osmosis.

   

• Blisters that are dry and hard are probably caused by air or solvents being entrapped during paint application and have no effect on the fibreglass.

   

Even if blisters are not visible, osmosis may be under development as it takes some time before blisters appear. Therefore it is advisable to get the hull inspected by a professional.

In the case of osmosis, a repair treatment should be carried out as soon as possible to avoid progression of the process.

Osmosis may affect any fibreglass boat (as corrosion affects steel), and it is very important to protect the hull and bilges well. Incorrect protection may damage the boat.

Osmoshell

 

Two-pack solvent free epoxy coating reinforced with glass flakes providing very high structural strength and superior adhesion to polyester substrates. Excellent abrasion and water resistance. Specially designed for osmosis treatment, but it is also suitable for bilge protection thanks to its very high chemical resistance. Can also be applied on metal substrates.

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