-
7.1. Three ingredients essential in the "osmosis" process.
7.2. The old blowtorch method: effective but dangerous.
7.3. Gel coat peeler effective under certain circumstances.
7.4. Risk factors cause the "dry and shield" method to fail.
7.5. Watershield reverses water molecule flow.
7.6. Importance of glycol removal exaggerated.
7.7. Glycol in re-appearing blisters cause warranty refusal.
7.8. "Osmosis" repair leaves voids in the FRP.
7.9. Pros and cons of grinding.
7.10. Pros and cons of blasting.
7.11. Both grinding and blasting create a mess.
7.12. Misleading statements made by paint manufacturers.
7.13. Only one way for an owner to save costs.
7.1. Three ingredients essential in the "osmosis" process.
We now know, that three ingredients are essential for "osmosis" to develop: Water, styrene and uncured polyester.
Molecules of all three substances must have direct contact with each other in order to start the process.
7.1.1. Common repair methods focus on water removal.
Most "common" "osmosis" repair methods are focused upon removal only of the moisture and sealing with a water shield.
Styrene and uncured polyester will remain in the laminate. Repeated high pressure washing during the drying period, which nowadays is recommended, may with some luck remove acids and other contaminants.
The dangerous styrene enclosures and uncured polyester will remain and water always finds ways of return even if the outside of the hull is shielded.
Further any material, epoxy or other, which cures at normal temperature will become an absorbing substrate and let water through at some extent.
7.2. The old blowtorch method: effective but dangerous.
An exception to the above is the old blowtorch method, which when used with skill provided easy removal of gel coat and degraded top laminates. Simultaneously styrene and acids were burned out and most of the uncured polyester cured.
Re-laminated with normal polyester and coated with gel coat or polyurethane, hulls treated in this manner seldom blister again.
The heat may cause deformations of the hull, loosen inside fittings and cause de-laminations in the FRP. There is also a risk to set the hull and the premises on fire.
Because of such hazards the blowtorch has hardly been used in the last 20 years.
7.3. Gel coat peeler effective under certain circumstances.
Another exception is the "gel coat peeler" if used to peel not only the gel coat but also all degraded FRP layers.
After peeling the hull is dried, then new FRP layers are applied and covered with water shield material.
If the drying is properly performed, this method cures "osmosis" type 1 to 100% and even type 2 if the process has not started in the remaining layers.
The method is expensive and does not cure type 3.
7.4. Risk factors cause the "dry and shield" method to fail.
The most commonly used methods are the "dry and shield" based ones, promoted by yacht paint manufacturers.
By proper sandblasting or gel coat peeling the infected FRP is opened up enough for the residues and moisture to be extracted during the drying phase.
A water shield coat then may be effective, but many risk factors remain which can cause failure.
7.4.1. Fatal residues remain due to too shallow treatment.
The moisture meters do not react to the styrene enclosures. As a result it can not be known if any such enclosures were left unopened by the blasting.
Acid contaminants can hide under a thin FRP layer without affecting the meter.
7.4.2. Open air drying only.
Many hulls are dried only in the open air. After the water shield coating, such a hull will still have at least the same moisture as the air.
If acid and styrene are left inside, this moisture is enough to start the "osmosis" process again.
7.5. Watershield reverses water molecule flow.
There are many "forces" involved in the moisture movements in a FRP laminate. The main ones are three:
- Displacement pressure from the seawater.
- Absorption and capillary action inside the material.
- "The cold wall" principle.
7.5.1. Capillary flow direction depends on fluid supply.
In capillaries the fluid will flow from the entrance with the richest supply to the more dry side.
7.5.2. Displacement pressure dominates in a gel coat hull.
In a sound laminate the displacement pressure forces moisture through the gel coat and into capillaries along the fibre strands.
Some of the moisture will collect in laminate voids, but most of it will pass right through and evaporate on the inside. A few months after launching the water content in the laminate stabilises at a relatively low level.
When the boat is inhabited, condensation will form on the interior hull surface. The combined displacement, absorption and capillary forces in the laminate dominate over the "cold wall principle" and the condensation build up cannot enter into the laminate.
Instead it will dry when the boat is not inhabited and chill the inside surface, which accelerates the moisture evaporation from the laminate.
7.5.3. "Cold wall" principle dominates in an epoxy coated hull.
To begin with the "cold wall" principle will reverse the moisture movement.
The water shield prevents the water entrance by displacement pressure. Instead the "cold wall principle" will take command and force moisture from the inside condensation through the top coat into the capillaries.
Since the water shield coat most of the time is cooler than the inside of the hull, combined capillary and cold wall forces bring the moisture into the laminate and against the water shield.
Now the moisture will need more time to escape out through the water shield than to enter on the inside and the laminate will hold more moisture than by a gel coated hull. Lots of voids and dry fibreglass spaces are left from the repair and will be filled with water.
This reversed water accumulation is normally very slow, but develops rapidly in boats inhabited on a regular basis!
7.5.4. The hydrolyse accelerates.
The reversed moisture entrance is spare but more than enough to feed the hydrolyse process.
The acids formed will now remain almost undiluted. The innermost woven roving layer and the layers nearest to the water shield will within few months be severely hydrolysed.
7.5.5. Moisture movement reverses again.
Commonly the inside of the deepest roving layer de-laminates. The de-lamination creates an insulation from the warm inside and the outside water pressure becomes stronger than the"cold wall" principle.
The sea water starts entering like earlier through the gel coat, but slower.
7.6. Importance of glycol removal exaggerated.
Some manufacturers of "osmosis" treatment products stress the importance of removing all glycol residues in the laminate, since they are highly hygroscopic and supposed to attract water.
7.6.1. Total glycol removal impossible.
Such a complete removal is impossible in all but the most superficial "osmosis" cases. Even the best steam wash will reach glycol residues in outer laminate layers only.
7.6.2. Glycol will keep water away from the process.
As has been mentioned earlier, the glycol molecules are too big to be able to move out of the voids where they were formed. The resulting lack of space means that they can only absorb a small amount of water.
Even if the amount is insignificant, this water can not take part in further hydrolyse of the polyester.
7.6.3. Glycol can't be removed from cured surroundings.
No washing can bring enclosed glycol out of the FRP before the cured polyester and salts surrounding it has been degraded and hydrolysed!
Since this glycol takes no part in the "osmosis" process a removal is of no importance. Instead the glycol prevents the space from being filled with pure water, which in turn could cause freezing damages.
7.6.4. Glycol acts as a barrier to aggressive substances.
The HYAB research revealed that glycol always forms inside of the "osmosis" source and actually protects interior laminates from the aggressive substances!
7.7. Glycol in re-appearing blisters cause warranty refusal.
"Osmosis" reappearing after a proper water shield treatment may show blisters in the epoxy coat that contain glycol instead of acid.
In such cases the "osmosis" has reccurred in styrene enclosures deep in the laminate fed with water from inside condensation.
Therefore the glycol forms outside of the enclosures. The aggressive substances, now on the inside and under pressure, can not penetrate the glycol barrier.
The pressure forces glycol and salts in front of the acids through the numerous cavities and degraded material, which remain after the earlier repair, into blisters in the epoxy water barrier.
The glycol found in such blisters is newly formed, but often insurance claims are refused on the grounds that the glycol was never removed properly during the repair.
7.8. "Osmosis" repair leaves voids in the FRP.
Even if moisture and acid contaminants are completely removed, dry fibreglass pockets and voids will be left in the laminate.
Besides causing a substantial loss of strength in the hull, such spaces sooner or later will become filled with water, due to capillary effects.
This water can lead to a re-appearing "osmosis" and even cause freezing damages.
7.9. Pros and cons of grinding.
Most amateurs and many yards prefer to use a grinder to open the damages..
7.9.1. Grinding causes heat that extracts styrene.
Grinding as opposed to blasting has the positive effect, that the created heat burns out the styrene at least two FRP layers deep!
7.9.2. The skilled grinding operator finds "osmosis de-laminations".
The grinding heat makes the de-lamination areas, caused by the "osmosis", visible to operators aware of this problem. Overlaying laminate then can be ground and/or ripped off.
7.9.3. Grinding extends drying time.
Unfortunately the grinding heat also melts the surface material, which leaves a "skin", that substantially extends the drying time.
7.9.4. Grinding needs much patching and filling.
After grinding extensive fibreglass patching and filling is required to obtain the proper shape of the hull
7.10. Pros and cons of blasting.
Blasting is not as simple as just a difference between dry and wet.
7.10.1. Dry sand blasting mostly is performed far too shallow.
Just to blast away the gel coat blisters is absolutely useless. All of the gel coat and degraded laminate material must be removed.
With luck all harmful "osmosis" residues may then be washed out of the laminate.
7.10.2. Dry sand blasting does not expose "osmosis de-laminations".
Laminate layers with dry fibreglass underneath are not found during dry sand blasting. Instead the blasting agent is apt to bounce of such areas with less cutting effect.
An experienced operator may be able to detect dry areas by the sound, but unfortunately most dry sand blasting is performed by contractors with little knowledge of "osmosis".
7.10.3. Dry blasting does not remove deep enclosures.
In order to remove styrene enclosures, sand blasting must be followed by a heat treatment like HYAB or IR.
7.10.4. Common wet blast equipment slow and expensive.
Wet blasting equipment to be fitted to pressure wash units easily opens gel coat blisters, but this is far from enough for an "osmosis" treatment.
To remove all gel coat and degraded laminate with such equipment requires much too much time, sand and nozzles.
7.10.5. Special "slurry" machines needed.
Wet blast equipment with 300-350 bar capacity and a carborundum nozzle is most suitable, as it removes all degraded material as well as gel coat but only slightly effects sound laminate
The damaging "osmosis" residues are effectively washed out by the high pressure water flow and most "de- laminations" can be detected and cut out.
Most effective are the now available combined air and water pressure slurry machines.
7.10.6. Wet blasting does not remove deep enclosures.
Like dry sand blasting, wet blasting can't remove styrene enclosures in the remaining sound laminates. Even if no acid remains, just one styrene enclosure of the trigger type may start up the entire "osmosis" process again.
7.10.7. Wet sand blasting does not affect drying time.
Much of the glycol and salts which normally slow down drying, are removed by the high pressure wet blasting.
Therefore extra drying time is not needed.
7.10.8. All blasting leaves sand in laminate.
Quite a lot of sand or other blasting media become embedded in the laminate after a blasting treatment. No tests have been performed as to the influence of such added contaminants, but because the sand is inorganic and closely related to the fibreglass, they are probably harmless.
7.11. Both grinding and blasting create a mess.
Grinding and sandblasting are both messy jobs for the operator. The object itself and the surroundings must be protected by covers.
Afterwards time consuming cleaning of the area is needed.
7.12. Misleading statements made by paint manufacturers.
Promises made by paint manufacturers in their advertisements have misled many boat owners to buy the resins and do the job themselves, in order to save money. The owners are advised to grind and sand away the gel coat before drying.
Occasionally articles about "osmosis" in yachting magazines recommend only to sand off the visible gel coat blisters before drying.
Even the best drying equipment is unable to dry a FRP hull treated that way, much less to evaporate styrene and "osmosis" residues! The "osmosis" will sooner or later return and the owner has wasted both his time and money!
7.12.1. Some yards recommend "DIY" treatments.
During the last years quite a few boat yard operators have refused to handle "osmosis" jobs because of the messy job and the "not explainable" failures.
Instead they often just provide the materials and recommend the boat owners to do the job themselves.
7.13. Only one way for an owner to save costs.
The only way a boat owner can save money and still get lasting results, is to use a professional for the opening and drying phases and the first priming.
Afterwards he may do the filling, sanding and paint work by himself.
