FYI, it isn't actually osmosis. Osmosis is the movement of a liquid through a semi-premeable membrane down the concentration gradient. Boats and other submersed fibreglass constructions suffer from osmosis. Unless you keep your car in the bath you can't get it.
My dad re-sprayed his MG in the late 80s in his garage. He didn't prep the body properly nor spray it in a dry environment and it shows exactly the same symptoms as the paint on our cars. It is the quality of the painting and painting environment, not the clam.
Anyone brave enough to get a scraper out and scrape off the paint on the affected area will see that it is where the paint has lifted from the clam, not damage to the clam itself
This has been debated a lot on here. The misconception is the bubbling is osmosis. However, as we have been discussing, there is probably a degree of moisture from the air transferring through the gel coat into the GRP. This would be classed as osmosis I believe.
Only if the clams were constructed in a completely moisture free environment, which they shouldn't have been. The part lacking in the osmosis is the concentration gradient. Plus you would need an awful lot of water in the air to cause it in that direction. It's possible (although unlikely) that the clams produced in the winter may get osmosis from the clam into the air, but it is almost definitely the quality of the paint above anything else. We don't really have large enough fluxtuations in water ppm in the air to cause it on a perceivable scale in the UK.
For the record I have none on mine (2001 N/A), but I do have a couple of areas where the paint has lifted from the surface of the GRP.
