What is fiberglass osmosis and how can I prevent it?


Fiberglass osmosis presents itself as a small round bulge on a fiberglass hull. This phenomenon is due to water diffusion through a permeable hull. Small air bubbles trapped within the fiberglass structure during construction are the starting point for osmosis. Osmosis has multiple causes; the production process, the quality of the materials used or a resin with low waterproof capacity. Blisters that have formed within the layers of fiberglass laminate are considered lesions of the hull and should be treated.

It’s possible to apply a preventive treatment in order to slow the appearance of this phenomenon. After hauling and securing your pleasure craft, the following steps are carried out:

  • Stripping of the anti-fouling layer in order to expose the underlying layer of gel-coat;
  • Surface preparation through sanding; 
  • Pressure washing with fresh water and specific detergents;
  • Application of an epoxy primer anti-osmosis treatment;
  • Application of an anti-fouling primer; 
  • Final application of three layers of anti-fouling.  

This preventive treatment offers superior waterproofing to the fiberglass hull.


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