Cause
Osmosis is generally associated to areas where fibreglass and polyester resins have been uses.
This system, used in the production of modern yachts is where Osmosis is most likely to occur but also
precast structures such as GRP Swimming pools.
GRP Swimming Pool due to small pin holes left in the laying of the glass fibre weave. This same type of problem can occur in wall surfaces when moisture pressure from the reversed side of the structure has not been sealed and allowed moister vaper to enter to bare untreated substrate.
This is related to the external cavity walls where the air movement within the cavity maybe restricted.
Initially small blisters become visible and over a period of time increase in size.
For example this problem can also occur where GRP and Cementous concrete swimming pools have been used and when in situ the revers side has not been sealed.
The water pressure present in the surround ground level can cause moister ingress into the substrate and blisters of the paint coatings occurs
Remedies.
Before remedial work is carried out the and retreated the moisture content should be below 12%
For further information on Osmosis: https://www.yachtingnews.com/osmosis