Cause
Osmosis is generally associated where fibreglass and polyester resins have been uses.
This system is used in the production of modern yachts where Osmosis is most likely to occur.
The cause is where moisture ingress into small voids which occur during the fibreglass and polyester system.
Initially small blisters become visible and over a period of time increase in size.
For example this problem can also occur where concrete swimming pools have been
constructed and the inner areas coated and where the outer membrane has failed.
The water pressure present in the surround ground level caused moister ingress into the substrate and blisters of the paint coatings.
Remedies.
To concrete structures where Osmosis has occurred the faulty membrane should be replaced and the defective coating removed back to a clean surface. Followed by repainting one the moisture content of the substrate is below 12%.
For further information on Osmosis: https://www.yachtingnews.com/osmosis