Osmosis Overview
GRP construction has been around since the 1950’s and has proven to be the most forgiving (if used correctly) and most cost effective production material in boat construction.
The wonder product of the 20th century was touted as the perfect boat building material. And then, hulls started to blister. The name osmosis was coined as the root cause of the blistering problem.
There have been claims that completely contradict the theory that osmosis in GRP actually exists. On top of this, surveyors have run moisture meters over hulls and sagely concluded that the hull has osmosis without any other supporting evidence. It is little wonder that boat owners, repair yards, insurance underwriters and surveyors get confused.
What is known:
- GRP is not waterproof. No resin is fully waterproof; liquid will be absorbed in varying proportions into the laminate through the gel-coat.
- If there are problems with the construction of the laminate, then this will increase the chance of blistering.
- One of the big issues with polyester resin is that it does not fully cure. Any un-reacted chemical group will increase the permeability of the laminate.
- Removing moisture will not cure a blistered hull.
- Blistering can decrease the laminate strength of a hull but unless the boat has a saturated core which is breaking down such as wet or rotted balsa, the presence of blisters does not necessarily mean that the boat hull is in immediate danger of failure.
- It is possible to have a laminate high in moisture with no indication of blistering.
- There is no direct correlation between high moisture meter readings and laminate condition.
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