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3.1. The laminate of a launched hull absorbs moisture.
3.1. The laminate of a launched hull absorbs moisture. Outside water pressure and interior capillary forces cause FRP laminates to absorb water, mainly saturating the fibreglass but also water molecules can enter into the molecular sysem of the cured polyester resin (see 4.6.). Not enough to sink the boat or even be noticed in the bilges but it adds a little to the weight of the boat. Further the water hydrolyses the coating on the fibreglass and creates capillaries along the glass strands.
3.2. Trapped substances always exist in FRP laminates. Trapped styrene, small amounts of crystallized by-products formed during the curing and sometimes microscopic glycol residues are found in all polyester laminates. 3.2.1. Styrene enclosures covered with uncured polyester. Styrene enclosures are always covered with a globule of uncured polyester which can not be penetrated by the water molecules.
3.3. Water can only enter along a penetrating fibre strand. Only if the styrene/uncured polyester globule is pierced by a fibreglass strand, can water enter and cause a chemical reaction. 3.3.1. Hydrolyse of polyester causes pressure. Water and styrene together causes an hydrolyzation of the large compact polyester molecules into a multitude of much smaller but more space demanding acid and alkali molecules. Thus a pressure is created that forces the new molecules to pass out into the surrounding laminate. 3.3.2. Earlier theories expect molecule passage to the sea. Earlier theories expect that the smallest alkali molecules move so fast out into the sea that no reaction with the bigger acid molecules occurs. This is supposed to explain the formation of the pthalic acid surplus.
3.4. Extended research reveals unknown damages.
The HYAB research team found, that the alkalis instead of leaving the laminate were dissolved in the moisture which always moves inward along the fibre capillaries in the laminate. When examining this, it was also found, that fibreglass strands in the inner laminate layers could easily be drawn out of the resin with a pair of tweezers! 3.4.1. HYAB tests show severe loss of strength. When comparing the results from all the tests, done by ourselves or at independent testing institutes, figures were found that clearly contradicted any earlier theory! In all the tests of "osmosis" type 1 with only the two top FRP layers visibly affected by "osmosis" the samples prove to be appr. 30% weaker than an unaffected FRP. Consequently one expects unaffected samples from the same hull to show the same 30% loss of strength if the two top layers have been peeled or grinded away. On the contrary here all tests prove only 8 - 14% loss depending on thickness of the samples. As the "osmosis" samples, of 8, 10 and 12 mm thickness, prove almost an equal 30% loss of strength, the total depth of the FRP laminate must be affected by the "osmosis"!
3.5. The last missing link in the "osmosis" chain 3.5.1. Loss of strength caused by the alkalis. Extended tests revealed that the alkalis stay in the laminate and causes the observed loss of strength. For the first time a complete description of the start of the"osmosis" process can now be presented. 3.5.2. Alkalis loosen the polyester / fibreglass bond. Som very small alkaline molecules move quickly along the capillaries between fibreglass and polyester. Together with water molecules the alkalis form a lye, that dissolves the bond between the fibres and the polyester, thus weakening the laminate considerably. The bond mostly consists of polyvinylacetate (PVA). Also in sound laminates intruding water slowly hydrolyses some of the PVA into vinyl and acetic acid (so-called aging or fatigue). This causes a 5 - 10% loss of impact and bending resistance after a number of years (see TNO test 9.1. page 34). With the alkalis present the process is incredibly fast and the loss of strength more than doubles. The space in the capillaries is considerably widened from the process but still it is microscopic. 3.5.3. Acetic acid causes the typical smell of "osmosis" The PVA substance constitutes a very small percentage of the FRP and, in contradiction to earlier theories, the acetic acid formed is of no importance in the "osmosis" process. Its small molecules however move very freely, where water is present, all the way into the outer laminates and later into the gel coat blisters, where they cause the typical acrid smell. 3.5.4. Glycol and salt form "border zone". A large amount of the alkalis reacts in a normal way with acid molecules forming new bigger molecules of neutral salts and glycols. The type of salt differs continuously during the process. The glycol is mostly propylene or neopentyl glycol depending on the type of polyester. Sometimes also small amounts of hexylene glycol form. This is a very agressive solvent which can enlarge the capillaries and speed up the process. With the exception of the hexylene ones, the big glycole molecules are not able to pass along the fibres. Instead they fill the space left by the dissolved globule and neighbouring enlarged capillaries, blocking the entrance of the surplus acids. 3.5.5. Formed salts and glycols cause research confusion. The large amounts of glycol and salts have caused most of the confusion and rumours among "osmosis" specialists. All earlier serious research reports regarding genuine "osmosis" affected FRP mention, that the "osmosis" samples contain much more water soluble materials, "WSM:s", than does the sound FRP. It was concluded that the "osmosis" is caused by such impurites being embedded during the manufacturing! To-day when we know how large amounts of "WSM:s" which can be created by the hydrolysis, it is easy to understand that they could not possibly originate from the construction! 3.5.6. Acid/styrene/water break down all enclosures. The pressure is somewhat released when the larger molecules are formed. Still it is high enough to force water mixed styrene and surplus acids (mostly pthallic origin ones and acid solutions of salt in water) to move laterally in the affected laminate layer. On its way the mixture will encounter further styrene enclosures. Previously the water needed a strand to enter and mix with the styrene to start the process. Now the mixture already contains all the substances needed to break down the uncured polyester globule from the outside and therefore also the enclosures without penetrating strands are hydrolysed. 3.5.7. The acid mixture spreads sideways in the layer. Trying to move inward, the first entering acid molecules meet alkali molecules that have penetrated the capillaries in the deeper laminates. The "osmosis" process (which in fact has no relation to genuine osmosis) accelerates from enclosure to enclosure and the laminate layer becomes affected all over the underwater hull. 3.5.8. The acid mixture breaks down cured polyester. As the acid content grows, it will slowly break the curing links in the cured polyester. This releases additional styrene and uncured polyester which in turn can be hydrolysed. 3.5.9. Only when the total layer is affected, blisters form. Not until all capillaries and voids in the first affected laminate layer are filled, the pressure is reached which can form the gelcoat blisters. 3.5.10. Size of blisters is no indication of damage state. Size or frequency of blisters does not indicate the severity of the breakdown process, only the properties of the gel coat. Thick or solid gel coat often shows more and bigger blisters than thin and porous. It is just a balance between pressure from the inside, time needed for the residues to pass through the gel coat and gel coat elasticity. 3.5.11. Blisters may disappear after a while. At this stage the "osmosis" process slows down considerably, because only cured polyester remains to "feed" it in the affected layer. More residues leak through the gel coat than what are created in the process and the pressure decreases. In many cases the blisters disappear until also the second layer has been totally affected. 3.5.12. Weight of hull forces water into the neutral zone. Until now the pressure from the process has been higher than the pressure from the hull on the outside water. As the pressure decreases, water as moisture will pass through the gel coat into the "water hungry" salt- and alkali solutions in the inner capillaries. The glycol molecules on the contrary are so big that they can not migrate into the capillaries. They are "imprisioned" in the original styrene enclosure space. Just a few added water drops will be enough to fill any surplus space and stop further water entering into the glycol filled enclosures. The pressure involved can not cause any delaminations! An exception is where a layer by construction has been allowed to cure before the following layer was applied. Then often the bond is so weak, that the total outer layer can be de-laminated from the inner laminate also from this moderate pressure.
3.6. Present "osmosis force" theories are impossible!
3.6.1. Explanation of osmosis. If solutions of different concentration are separated by a permeable wall, solide with holes or an absorbing substrate, they will pass into each other until the concentration equals. No pressure or different amounts on the two sides will arise. If the solutions instead are divided by a material which will only permit molecules of the solvent, in this case water, to pass through (semi permeable membrane) only pure water molecules from the low concentration side will pass into the high concentration solution until the concentrations equals. This phenomena is called osmosis. When a certain pressure is applied to the high concentration side the passage will stop. This pressure is called the osmotic pressure and depends of the difference in concentration between the two solutions. In the first example above the contrapped air will be compressed by the water molecules entering the high concentrated solution until the osmotic pressure is reached, then the process stops. The second and third examples shows how the weight of the high concentration solution creates the pressure wich stops the process if the two surfaces are not closed in. 3.6.2. Gel coat is not a semi permeable membrane. The osmosis is never relevant in a fibreglass hull. The gel coat is an absorbing substrate (even if it is less absorbing than the laminate) and will let water out or in as moisture together with most of what is dissolved in it.
As well as lower concentrations from the outside will pass into the laminate, eventually higher concentrations inside the laminate will pass out until the concentration equals. If the water on the outside, like under the weight of a boat hull, is under pressure, moisture will be pressed through the gel coat into the laminate. After that the laminate has been saturated and eventually delaminations filled, the same amount of moisture which This will never cause any pressure within the laminate or between laminate and gel coat as supposed by earlier presented theories.
3.7.Chemical reasons for polyester to hydrolyse. Lower esters can be formed just by mixing acid and alkali molecules under de-hydrolyse e.g. removal of a vater molecule during the process. For high molecular esters used for polyester resin different glycols are used instead of pure alkali. Also those glycols are de-hydrolysed during the manufacturing process. During the mixing with the acids, further de-hydrolyse will occur. 3.7.1 The ortho ester molecule. The ortho ester is formed by mixing one phthalic acid molecule with two propylene or ethylene glycol molecules during de-hydrolyse of two water molecules. The orto ester now has one molecule group on each side where only addition of a water molecule will form glycol again. Also the center group can be hydrolysed by one or two watermolecules. The result will be a mixture of phthalic acid, alkalis, salts and lower and higher glycols.
3.7.2. The iso ester molecule. By mixing two of the smaller isophthalic acid molecules with only one bigger neopentyl glycol molecule the iso ester forms without dehydrolyse and should be less apt to hydrolyse. Only one side of the molecule has a group which can be hydrolysed to glycol. However if we look closer at the iso- phthalic acid molecule it is just a de-hydrolysed normal phthalic molecule! The iso polyester is better than ortho in many aspects. Less uncured enclosures with lower amount of "triggers" might slow down the start of the hydrolyse but when it starts, double the amount of the agressive acids forms. The laminate often gets worse so called "osmosis" damages than the ortho types.
Earlier iso types also formed more of the dangerous "dangling chains", as any end of the molecule could add to the end of the next molecule when the polyester chains formed. Later types have an oxygene or a carbon dioxide molecule added to the iso phthalic acid, e.g. terepthtalic acid, which reduced this problem. 3.7.3. Polyester production. As the name indicates, the polyester molecule is formed by a large number of ester molecules "glued" together as a chain.
As longer the chains as more solide the polyester will be at room temperature. The boat construction polyester molecules must have a certain "high molecular" length in order to obtain sufficient hardness after the curing. The "virgin" resin has a far too high viscosity to be used for laminating and a solvent must be added. The styrene which must be added in a certain amount for the curing process is also a suitable solvent. By adding a surplus amount of styrene, the viscosity is brought down to a suitable level. All of the substances used when creating the polyester resin are highly reactive and instable. So is also the resin itself. Especially are all of them "water hungry" due to the many dehydrolysing steps involved during production. Normally the curing and post curing will make the material stable and water resistent. Now the post curing is abandoned and as mentioned before, lots of uncured polyester, styrene and other reaction products will remain in the laminate. 3.7.4. The polyester curing process. When a small amount of methyl ethyl ketone peroxide is added to the polyester resin, a reaction starts, where pairs of molecul chains are cross linked by MEK and styrene molecules. The molecular weight raises and the resin becomes hard e.g. cures. Only part of the styrene is used for the cross linking. The rest is supposed to escape from the laminate during the curing period.
After the normal temperature curing in the mould, the result is demonstrated in the above schematic illustration. Only part of the surplus styrene escapes. The rest forms small blisters surrounded by a thin skin of uncured polyester entrapped mainly in the outer laminate layers. Some polyester chains remain incomplete cross linked. Most of them lose the normal glycol end which is replaced with a phthalic acid molecule e.g. "dangling chains". The free glycol, not used styrene and MEK will remain within or close to the faulty molecule for about a week. If within this week the laminate is heated for a short time to 80°C, the skin around the styrene enclosures as well as the incomplete cross linked chains will cure properly and all excess styrene will evaporate. In a not post cured laminate, uncured polyester and products formed by the other remnants will invite water to start the "osmosis" e.g. hydrolyse. The acid formed by the hydrolyse will break the dangling chains into substances, which in turn can be hydrolysed. When acid and styrene are sufficiently concentrated, also properly cured molecules will be broken and hydrolysed. The normally hard laminate turns into soft wet fibreglass. 3.7.5 Illustrations of first stage FRP hydrolyse Shown below a schematic cross section of the gel coat and the two first laminate layers from an "osmosis" affected FRP laminate. Note! The capillaries along the glass fibres are extremlyenlarged in order to provide visibility!
Fig1. Inside the gel coat Variable numbers of styrene enclosures The displacement pressure slowly forces sea water through the gel coat. The molecules collect to moisture in the capillaries along the glass fibres. High water content
Fig 2. If the laminate contains one or more styrene enclosures penetrated by fibreglass strands, the scene differs: Here the inside of the skin is weakened by the styrene and can be attacked by the water. The uncured polyester is hydrolysed into smaller but more space demanding acid and alkali molecules.
Fig 3. In need of more space a part of the small alkali molecules are forced out into the capillary system before they can react with the acid. The remaining alkalis react with acid and form salts and glycol A surplus of acid and styrene remains and is forced out into the capillary system in the outer laminate, where they mix with existing water.
Fig 4. When the acid mixture reaches the next enclosure, it contains styrene enough to weaken the outside of the skin. Therefore, once the process has started, all enclosures in the affected layer are hydrolysed. This highly accelerates the process. Further the phthalic acid part of the mixture is able to break up the curing links in the cured polyester. This is a very slow procedure but it will produce new amounts of styrene and uncured polyester to feed the hydrolyse. This property of the acid is also the main reason for the re-currency of the "osmosis" after a repair!
Fig 5. The acid mixture spreads along the fibreglass strands from enclosure to enclosure in the outer one or two laminate layers all over the underwater hull. Once started, this "osmosis" process phase proceeds very fast. In a few months the affected layers can be totally degraded without any visible sign! Already now the alkali lye, mentioned in fig 1, has spread within all the inside layers. The binding between fibreglass and polyester is severely damaged and the hull has lost 20-30% of its strength.
Fig 6. With no more expansion space along the fibres and with all inward directed capillaries blocked by salts and glycol, the process pressure increases. It will totally stop water from entering through the gel coat and instead cause the acid fluid to seep out. As this is not enough to even out the pressure, the elastic gel coat will now form the characteristic blisters. At this stage the blisters will seldom be bigger than 1 - 15 mm. The size actually depends on the gel coat quality, not on the state of the hydrolyse. A bad gel coat allows more pressure to escape and forms smaller blisters than a good gel coat. If bigger than 15 mm blisters are found, the process most likely has reached into deeper laminate layers.
Key to colour coding
Fig 7. When all uncured polyester in the outer layer(s) has been hydrolysed, the process slows down and no more pressure forms. Very often the gel coat is elastic enough to let the blisters disappear until deeper layers are affected. During this phase of the process pure outside water will penetrate the gel coat and dilute the salt solution on the inside. The original inward movement of fluid in the capillaries is restored and also the fatal acid/styrene mixture follows the water into the next laminate layer. Thus the hydrolyse process will repeat layer by layer until at last only wet soft fibreglass remains instead of the solid hull! Note! Especially if moist fibreglass or heavy woven roving have been used in the construction, the hydrolyse can also start in an enclosure deep inside the laminate! Only the fibreglass mat remains without attachment to the surrounding layers (total de-lamination).
3.8. "Osmosis" spreads differently in deeper layers.
3.8.1. Typical mushroom shaped damages form. When the "osmosis" expands into deeper laminate layers the process alters considerably. Instead of spreading equally inside a total layer, it forms the typical mushroom shaped spot damages well known by "osmosis" repair operators. 3.8.2. More available space reduces the acid. The hydrolyse process as before creates large amounts of acids, alkalis, glycol and salts. As much of the inside capillary space is already occupied by alkalis from the top layer process, less of the newly formed alkalis can escape this way. Instead they react normally with the acids, which results in less acid surplus and more salts. Further, when the mass of new small molecules need more space, they can freely move out into the already degraded laminates. 3.8.3. Shrunken gel coat blisters become visible again. The hardly noticeable rise of pressure created from the new molecules will be neutralised by the elastic gel coat blisters. Earlier "disappeared" blisters will be visible again and remaining blisters will grow a little. 3.8.4. Mushroom stem is formed. The acid and/or styrene can only penetrate the neutral zone along one or more fibre strands which also penetrate the polyester tie-coat and into the next fibreglass layer. The passage will be widened as cured polyester slowly is hydrolysed. Since the process pressure is more or less equalised the aggressive fluids are not forced to move along the lateral fibre capillaries like before. If no styrene enclosures are situated in the very neighbourhood, the "osmosis" will go on hydrolysing cured polyester deeper into the laminate and slowly widen the "stem" as shown in the lower part of the illustration. (Fig. 8) 3.8.5. Mushroom caps are formed. When styrene enclosures are present near the "stem" in a fibreglass layer they will be hydrolysed like in the start in the outer layers and the process will spread laterally again. However much of the pressure will leak outwards and also less acid surplus will form. The spread of the damage proceeds much slower than in the outer layers. Instead of the whole laminate layer being destroyed, only somewhat circular damages form like mushroom caps as seen in the upper parts of the illustration (Fig 8). 3.8.6. New neutral zones make mushrooms fork. New neutral zones form on top of the "caps" which cause new "stems" to enter the underlying layers and so on. 3.8.7. Abundant enclosures cause wide "de-laminations". In laminate layers with large amounts of styrene enclosures all of the polyester within a "hat" area can be degraded and make it look unwetted or de-laminated. 3.8.8. In due time the hull will render completely soft. Without exception sooner or later an "osmosis" affected hull will be rendered to soft to be used. When gone so far it is also too late for a repair! 3.8.9. Illustrations of second stage FRP hydrolyse The "osmosis", or let us from now on use the more proper word hydrolyse, shows a different chemical behavior, when it proceeds into deeper laminate layers. Also the laminate lay up type causes significant differences.
Fig. 8 Visualises three different types of inward movement of polyester hydrolyse. (In reality they are of course considerably more spaced apart from each other.) Second stage damages in this type of laminate might be successfully repaired, like first stage ones, using a common dry and shield method, if all of the "mushrooms" are found, ground out and re-laminated. As the hydrolyse will spread again, if just one tiny "cap" remains somewhere in the laminate, the risk for recurrence is considerably high. The uncured polyester, acid, glycol and dry salts in the cap area will not cause any turn of the moisture meter scale, but the hydrolyse will start as soon as some moisture enters again. With the outside covered by an epoxy or other type of water-shield, the „cold wall principle" will cause inside condensation to enter into the laminate.
Fig 9. Visualises how the inside of woven roving mat layers are totally hydrolysed and de-laminated. When a mushroom stem reaches into a woven roving layer, acid, styrene and moisture will spread very fast into large areas of this layer. This spread is not caused by pressure but is due to capillary forces along the mass of extensive fiber strands. Instead of forming a local mushroom cap damage, in a couple of years one single stem can cause the whole layer to be hydrolysed and totally de-laminated from the next layer! In laminates with multiple roving layers, such de-laminations occur in many of the layers. The de-laminations are often square meter large and overlap each other. Especially in hulls earlier „repaired" for „osmosis", the de-laminated roving layers will totally even out the process pressure and no tale telling blisters are formed in the coating. The boat owner does not become suspicious until the boat behaves peculiar at sea or visibly deforms by drysetting. By then probably the repair warranty has expired. Already in a 50´ hull it is quite common that 20-30 liters of aggressive fluid are released if a test hole is drilled in an area where the moisture meter shows just a slightly higher reading than normal. If the damage stays deeper than 6-8 mm from the surface, an instrument with close spaced electrodes like the Sovereign, used by many surveyors, does not indicate any moisture at all! Analysis’s of test cores give very different results depending on laminate quality and type of polyester used. The worst fluid containing de-laminations are found in big ortho polyester hulls made in hot climate areas and where some laminate layers had time to cure totally, before the next layer was applied. Such layers de-laminate so early during the hydrolyse, that instead of a phthalic acid surplus an alkaline maleic anhydride surplus forms. The also formed dimetyl phthalate salt, will be diluted by entering water and then become slightly acid. In total the fluid will be anything from slightly acid to slightly alkaline, where alkaline signifies a bad lay up and acid a better one. This might seem contradictory, but the inward spread of the hydrolyse proceeds slower in a bad laminate than in a better one, even if the resulting de-laminations become worse. It can take 10 - 15 years before the inner half of the laminate is affected! Alkaline readings of fluids from inside de-laminations or pockets must not be confused with alkaline readings of fluid from blisters in an epoxy watershield coating!
The bond between the layers is severely weakened but total de-laminations deeper than 4 -6 mm from the surface are rare. A drilled test hole mostly only gets moistened by a fluid with a high content of phthalic acid. However stresses on keel and rudder often cause the weakened areas around them to de-laminate completely. Any attempt to repair a second stage hydrolyse damage in a roving type hull, using current methods, is deemed to fail. Dry and shield repair can even speed up the process by reversing the capillary movement of moisture in the laminate. The use of vacuum pumps to empty the de-laminations and/or peeling and applying of 4 - 6 mm of new laminate might result in a dry reading on a Sovereign or similar moisture meter and an approval from a surveyor, but the process will proceed inside the „repair". Usually it can soon be recognised by an acrid smell in the interior of the hull.
3.9. Time between "osmosis" start and first blisters. The speed of the "osmosis" process depends on material quality and surroundings. It may take anywhere from a few months to many years from when the "osmosis" starts in the first styrene enclosure until the first blisters appear. 3.9.1. A total layer may be affected within a few months. A bad FRP with many styrene enclosures may have the first layer affected totally around the underwater hull within a few months from the start, while a good FRP quality can need 10 years or more. 3.9.2. Temperature and type of water important factors. The environment has a big impact on the "osmosis". The hydrolyse process is considerably slower at temperatures below 15ºC and practically stops below 10ºC. Fresh water, especially when somewhat acid, causes a faster break down, than salt sea water. 3.9.3. Content of butyl alcohol is another important factor. The curing process always leaves residues in the laminate. One of them, dibutyl phthalate, reacts with water and forms butyl alcohol which is highly hygroscopic The butyl alcohol partly moves into the gel coat blisters, where it rapidly vanishes out in the water and partly into the neutral salt zone. The more alcohol in the zone, the faster the acid mixture can penetrate it. 3.9.4. Patent pending test technique developed. The HYAB team has developed a test technique, which shows exactly which layers are affected and to what extent. The operator can immediately tell the owner if the hull can be repaired with lasting result, what it will cost and exactly how long time the repair will take. Speculants on large expensive fibre glass yachts are strongly recommended to spend the cost for a surveyor who can perform such a test. Check with the author by e-mail hyab@lander.es 3.9.5. Patented repair technique developed. The research made it also possible to create a reliable, patented repair technique, the HYAB Osmocure which is described in the book "Osmosis" How to repair hydrolyse damages using the HYAB Osmocure technique" by the same author.
3.10. Hydrolyse does not create any de-laminating pressure. There exists a very strong belief among "osmosis" specialists, that an "osmosis pressure" causes the FRP to de-laminate. Osmotic pressure is instead the pressure needed inside a diluted substance to prevent pure solvent molecules from entering through a dividing membrane. Even if osmosis should have been involved the pressure would not be high enough to cause delaminations. The substances formed by the hydrolyse for certain do not create such high pressure. 3.10.1. De-lamination involved is a chemical degradation. By grinding, IR heating or use of the HYAB lance, often big areas of fibreglass without polyester, looking as if they had not been sufficiently saturated in production, are found. In reality they are caused by the hydrolyse process. 3.10.2. Heat is the best detector of the damages. When using heat type equipment, many operators do not understand, that they detect already existing damages. They believe that they have caused the "de-laminations" with the heat and therefore refrain from the use of the only equipment that provides a solution to the "osmosis" problem! 3.10.3. Forced or "osmosis" de-lamination? If an actual de-lamination caused by force is inspected, one can clearly see lots of ruptured fibreglass strands. By the "osmosis de-laminations" no such ruptures can be found. One must understand, that the dry fibreglass instead is what remains after that the "osmosis" process has destroyed all of the polyester!
"Osmosis" de-laminations
Forced de-laminations
It is absolutely necessary to open up and restore all such dry or fluid filled de-laminations during an "osmosis" repair. Some can be square meters large!
3.11. The "osmosis" process needs a minimum of water supply. When "osmosis" develops in the inner laminates it can proceed with just a minor water supply! Once started in an enclosure it draws moisture from a waste part of the surrounding FRP. Experience from re-doing a substantial number of boats, previously treated for "osmosis", has proved, that condensation on the inside of the hull is sufficient to maintain the process. Especially in yachts used year-round as quarters for many persons, "osmosis" often recurs within a year. Note that many types of epoxy watershields do not allow the restarted "osmosis" to form blisters!
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the laminate consists of cured polyester 
reinforced with fibreglass mats 
. 
covered by a layer of uncured polyester 
will always remain after the curing. Normally they cannot cause any harm. 
in the outer layers, low content 
in those further in. The capillary "force" transports the moisture inward right through the laminate. The same amount that enters from the outside evaporates from the inside. 
and spread very fast along all capillaries into the innermost laminate. The lye affects the binding between glass and polyester and the laminate gets substantially weaker. 
within the enclosure cavity and also clog the inward capillary openings. 
only moves sideways. Inward movement is stopped by salts and glycol. The outside water pressure prevents escape through the gel coat. 
