osmosis book web page

1. What causes "osmosis"?
2. Some trigger causes.
3. How "Osmosis" proceeds.
4. Why so many different opinions?
5. "Osmosis" effects on FRP hulls.
6. How to distinguish "osmosis" types.
7. Common repairs and recurrence Risks.
8. How to obtain optimal repairs.
9. Technical definitions and terms.

1. False belief in few recurrences.
2. The appearance of recurring "osmosis".
3. Repair of recurring "osmosis".

Exceptions possible.


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The results of a Million$$ research about
the so called osmosis problem which occurs in polyester/fiberglass boat hulls.

The research was performed 1992 - 1997 using test material from a number of hulls with different stage and types of "osmosis" damages. Over 600 test pieces of laminate were used for the purpose. Standardized laboratory tests were performed by one Dutch and two Swedish Universities but the most important contribution to the results was the new European laboratory of a large American paint manufacturer where we were allowed to use state of the art microskopes and strength test machines. Thus we were able to perform more important but not standardized tests without the enourmous costs to create standards for "official" tests. Those costs are probably the reason for that research on actual hydrolysis damaged material has not been performed earlier.

During 1994 - 1998 the research results were confirmed by repair of over 100 badly damaged hulls in the worst affected areas of the World. All of them but two have had no more problems. The two who recurred were due to mistakes by the repair operators at an early stage.

Edition 6 May 2002 ©Copyright 1995.
All rights reserved.
No part of this publication may be reprinted
without written permission from
The Author

For more convenient reading and better picture qualities you can download the original book in PDF format (2.499 KB)

If you have chosen the $17.95 alternative a CD will be sent by normal mail. Just send me an e-mail with "CD" in the reference field and your user name and password + name and direction in the message.


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For CD delivery: blomberg@osmosisinfo.com



Personage behind the research and the results in short.
This book is the result of the relentless work and research done by the retired boat yard owner Mr. Bengt Blomberg of Stockholm, Sweden and his team of laminate and coating specialists.

An offshore powerboat racer (Offshore2 world speed record holder 1969-93 together with his wife Heidi), active in the marine repair and boat building business for over four decades, Mr. Blomberg became familiar with the problem in the early 1970 ies. During the following 20 years his yard performed hundreds of so called osmosis repairs.

Over the years, he actively tested and recorded the performance of just about every known "osmosis" repair method; from propane burners, to grinding, sandblasting, peeling and infrared heat.

Mr. Blomberg was the first to use high pressure (350 bars) wet-slurry blasting systems for gel coat and blister removal, but the long -term results continued to be disappointing. The "osmosis" recurred to a greater or lesser degree and no method seemed to permanently cure the problem.

Initially, he accepted the explanations of the "osmosis"; problem provided by resin and coatings manufacturers, surveyors and other "experts"; and followed their recommended repair procedures.

Soon finding these methods and their associated theories to be inadequate and illogical, Mr. Blomberg set out to find the true reasons for and the chemical facts behind the problem.

A closer survey of all the many circulating different and confusing explanations of the problem revealed more of an industry that was anxious not to frighten presumptive boat buyers, than presenting the truth of it.

1953-64 Mr Blomberg was director of a major automotive chemical factory where he among else developed the first water-soluble detergent for removing of silicone contaminates from windscreens and delicate enamels. The formula is still widely used when cars are re-painted. Also a co-founder of the Swedish-German-Polish-US rust prevention research firm Safe Coat, Mr Blomberg had sufficient chemical knowledge and trade connections to be able to scrutinise the confusing information available about "osmosis"; and polyester related research.

A number of hulls with different stages of "osmosis"; damages were bought and cut into pieces for laboratory tests and strength comparisons.
Within a couple of years the team could present the exact reasons for and the chemistry behind the problem:

A polyester laminate needs "post curing"; at 80-90ºC in order to cure completely. Of economical reasons this is, with few exceptions, not performed at boat construction.
A not post cured laminate contains 10-15% uncured and not totally cured polyester resin. As described in the following publication, such uncured resin enclosures can be transformed into its original acid-alkali-glycol substances by adding of a few water molecules.
This is called hydrolysis, but has nothing to do with excess water entrance or faulty construction, as commercial sources have brainwashed us to believe for many years!

All laminates, perfect or with faults, with or without special "watershield"; coats, will absorb enough water to feed the hydrolysis. It is just a property of the material, which the mighty industry has used all means to hide from the consumers.

At this stage the research team became confused: What we had found was related to practically all produced GRP hulls. Why then were not all of them affected by the hydrolysis?
Could we be on the wrong way?

Another two years of numerous tests learned us a lot more of the so called "osmosis"; process but not what we were looking for: The trigger.

1992 Mr. Blomberg by sheer coincidence met a retired director of research at a major British resin manufacturer.
The researcher was familiar with the problem, having studied it in the early 1960 ies, as architectural FRP panels mysteriously had developed "lumps"; or "warts"; - what we today would call "osmosis"; blisters.

The studies at the time led to a better post curing technique, which remedied the problem.
The project was shelved and the findings were never made public.

The information gleaned from this study suggested a very important theory : Normally the uncured enclosures can not be affected by the water.
Occasionally specific "trigger"; enclosures of styrene covered by uncured polyester and pierced by a fibreglass strand exist.
The strand allows water molecules or even moisture to enter and react with the styrene diluted inside of the uncured polyester skin and the hydrolyse starts!

In order for a styrene globule to form around a strand, and create such a "trigger";, certain specific criteria induced during the manufacturing process had to be fulfilled.
Some laminates have no such "triggers"; and will therefore not develop "osmosis";, explaining the random nature of the problem.

Thorough testing of the "trigger"; theory was performed using remaining material from the earlier used test hulls. When test pieces from areas just over the waterline was split up into separate laminate layers, a few pin-head sized dark spots were found. The microscope clearly revealed enclosures with both the penetrating strand and the
hydrolysed resin.

After considerable time, effort and expense, this extensive research confirmed the validity of the "trigger"; theory, revealed the true cause of the problem and worst of all, found that the process causes not only "cosmetic"; blisters but also very severe damages deep in the laminate.

Important research results in short:

  1. Totally contradicting earlier theories, the "osmosis"; is not caused by excessive water entrance.
    There is absolutely no osmotic forces involved (the gelcoat is an absorbing material which can never act as an osmotic membrane)!
    It is the hydrolysis process, which creates the water soluble products and the cavities, which then allows for excess water to enter and cause the high moisture readings.

  2. It is the pthtallic acid, formed in the process, which causes the chain reaction and damages, not the water!
    The acid forms as not water soluble crystals and can not be washed out of the laminate as claimed by some epoxy suppliers.
    Even after years of hardstand and weekly washes, the acid will remain in the capillaries and cavities, dissolved in styrene and glycol.
    The hydrolysis will restart as soon as the hull is launched, how well watershielded it might be.
    The laminate can become severe damages before any warning blisters show up again.
  3. Long time tests proved: Contradicting earlier theories most "osmosis"; hulls, conventionally dried and epoxy coated without effective acid removal, become deep damages faster than similar hulls not treated at all!
    Excess water in the laminate does no harm! Instead, due to temperature differences in the surroundings, the water moves in and out and thus washes out a lot of the harmful residues.
    Further a free moisture movement in the laminate has a cooling effect which considerably slows down the hydrolysis.
    The hysteria about watershielding is created only by the heavy advertising about "perfect"; epoxy or other expensive (= high margin) products which should keep the water out.
    In reality no such product will do better than to slow down the water entrance 3-7 times more effective than the gelcoat.
    Therefore it can not stop the hydrolyse. It will only cover the problem in a way, that you will not se the warning blisters for a long time!
    Instead the coating decreases the above mentioned washing and cooling effects and accelerates the damages.
    A watershield coating without a total removal of acid remnants, styrene and uncured resin is a waste of your money to-day and will cost you a lot more in the future!
    If a proper treatment with controlled residue removal (just moisture meter control is of no value) can be performed, a watershielding is advisable.
    Not in order to stop hydrolyse, but to avoid weight increase for as long as possible after launching.
    When such a treatment is too expensive in relation to the value of the boat, our experience is:
    Do not watershield, just sand eventually blisters open once a year and apply antifouling only.
    This will retain de-laminations and the softening of the hull for much longer than an epoxy coating!
  4. "Osmosis"; blisters is really not a cosmetic
    problem only! They are just the vis