Rossynant
Well-Known Member
Depending what "osmosis" is
certainly not by what I know from biology... Quite frankly: laminate soaks water by a capillary action, it gets into places where glass is not completely filled with resin (never 100% possible), so if there is much porosity, then lots of water will get in. This water will dissolve some chemicals from resin, can also freeze and expand etc. So this may result in some delamination of material, in turn making it possible to get more water in, and so on.
Therefore quality is an answer, both resin quality and workmanship - glass must be saturated as much as possible. Sloppy work makes material more porous. Water travels along fibers, especially thick 'strands' as those are hard to get saturated inside. Capillary effect. Much less water can get across resin itself.
In older boats, made when resin was cheap, plenty of it was slapped on, there was much less fiber in laminate compared to "modern" ones. As strength of laminate depends on amount of fiber - later many methods were devised to save on resin amount, as this got expensive. So later laminates were thinner with same glass amount, but this may result in more porosity. Also such thinner laminate is less stiff.
So called osmosis was rare in boats made with clear resin, not compromised with whatever cheap mixed in, and thick layup, from before '70 year. Just some blisters in gelcoat only. Not much to worry, and anyway hulls had excess strength.
Then it got much worse when hulls started to be thinner - and I heard opinion from proffs this was caused by insufficient stiffness. Opinion was GRP must be designed to stay stiff. Once it flexes there is some cracking of gelcoat, glass detaching from resin, or breaking, micro-delaminations between layers - all this water can get into and act.
Then this idea was employed of making thin gelcoat (less cracks) reinforced by thin mat, this in more "resistant" iso resin. Then followed by structural laminate made normally (i.e cheaply as always). Interestingly this caused even more problems, because gelcoat and this first thin mat was made separately from the rest, with different resin, left a while to harden initially - so an area of possible delamination was created. Iso resin was indeed water resistant, so blisters formed behind it, between those layers, behind the first mat. And such were a bit bigger than just those old small ones forming inside the gelcoat itself
But all this is only skin deep.
More seriously: boat that had real voids, GRP turned to kind of wet jelly going almost all hull thickness (and thick it was) in few places; mentioned above. Worst at waterline. I'd say this was wrong mix or layup at the spot, soaked, then damaged by freezing. Going on they would sink the boat. Scraped off, patched with epoxy.
Boats (two sistership) that took water on launch, in second year... On examination areas were found (one at stern, other just after keel) with hardly a resin in layup! area of few sq feet, roving practically dry in places, mat a bit wet. Seem only gelcoat kept them on water before... Producer was contacted.
Boat that developed voids (big delaminations) inside the layup, after a few seasons. Discovered by sound. Were filled with thin epoxy through drilled holes, but after a season delaminated again.
Friend was involved with racing boats on Bodensee. Some were getting soft in outer layers of hull, so you could scrape the GRP off with finger. They were sanded down or planed, then few layers of new glass/epoxy. Without making new layers of good laminate over they would probably break.
But all this can be spotted before boat actually sinks. Unless no-one is watching.
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