The fact remains that in practice some yachts ‘get osmosis’ - ie
blisters, and some don’t. It is known that several factors increase the likelihood of blistering. These are
Long periods afloat without layups
Warm tropical waters
Fresh water is worse than
salt water
Coloured resins (including white - the most common) are worse than clear resins
Historically, there have been some batches of boats that have suffered severely from blistering. Often this was due to changes in
layup specification, and use of new materials. For example, it is now known that the use of PVA emulsion bound glass mats is bad practice. Emulsion bound mats were introduced in the 1960s as an improvement, and accepted by Lloyds and other classification societies for standards of
hull construction for almost 20 years. Emulsion bound mats are now regarded as bad, as the PVA is water soluble, and tends to encourage wicking. Mats used now should be powder bound, especially in the outer layers of a laminate. Nevertheless, plenty of yacht builders still use emulsion bound glass mat in inner layers of
hull layups.
Whilst some builders, including those who produce some very expensive boats, have had runs of boats prone to blistering, they have also turned out apparently identical boats that have not blistered.
Current thinking is that cleanliness, temperature and humidity control in the moulding shop, and precision of the mix of resins, are the key to building boats that will not blister. Nevertheless I know of one
builder who worked in a dirty corrugated iron shed where the climate control was dependent on whether an easterly
wind blows through the gaps in the door. His boats actually had a rather good reputation for ‘not getting osmosis’.
Sent from my HTC One_M8 using Cruisers Sailing Forum mobile app