Service ╗ Osmosis treatment
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What is osmosis?
Unfortunately, polyester laminate only looks watertight at the first glance. In fact, the molecular laminate
of the polyester contains enough permeations and holes to enable moisture to penetrate inside (diffuse). This
does not happen overnight, but over a period of many years. The individual layers of the hull laminate resist
the penetrating moisture in different ways.
Osmosis on the boat hull
The most watertight layer is the gel-coat. This coat should never be damaged, since otherwise, water
and moisture will be able to penetrate into the laminate directly unhindered. It would actually not be
a problem that moisture slowly penetrates into the polyester if the laminate were in perfect condition,
in other words, if it were without trapped air and air bubbles.
However, even the best plastic manufacturer will not be able to supply a laminate which is
absolutely free of bubbles. An this is where the actual problem starts.
These bubbles contain the residues of unhardened resin, hardeners and binders from glass wool mats.
The water (water molecules) which diffuses through the gel-coat into the laminate dissolves these
residues in the bubbles. The concentration of these residues is much higher in the fluid which is
created than in the laminate environment. This is when the osmosis process begins, as the different
concentrations attempt to offset each other. However, since the pure water molecules are smaller
than the molecules in the solution, they can also penetrate the laminate more easily and quickly.
The bubbles with the dissolved residues remove the
moisture from the surrounding laminate and collect it in the bubbles. When the bubbles are full,
they exert a pressure
which produces the typical osmosis bubbles in the gel-coat.
We specialise in preventing osmosis and in removing osmosis from GRP yachts For hulls with old
antifouling coats, we remove the entire old coat down to the gel-coat in order to carry out the
osmosis prevention procedure. This is lightly sanded, cleaned and checked for damage. We then
reconstruct the hull underbody in at least 5 layers, using a special tar epoxy primer as a protective
layer (water block), before the new antifouling layer is applied again as the final coat. The
material used is of importance during reconstruction. It should always be epoxy based, since only
epoxy is completely watertight. The temperature during the procedure also plays an important role.
Low temperatures during the procedure or afterwards during the hardening period are disastrous for
this material. The hardening process is stopped and the reconstruction work will have been carried
out for nothing.
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