Polyester hydrolisation (aka "osmosis")

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mortehoe

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A certain boat surveyor appointed for a buyer, scraped my hull 3 weeks ago, did a "moisture" test and declared the hull "very high" moisture reading = "Osmosis" was the predominant word that he said in his written survey report. ("non-laminar base-cellular-osmosis is probably present ..... etc ..." ..... Erghhh???????)

The same Surveyor did a report on the same boat 14 years ago and said the EXACTLY the same words affter making the same scrapes .....

.... the only difference was that the self same untreated hull neither had blisters then (1997) nor has blisters now.

How wide is his bog roll ????

So how can a blisterless hull have osmosis?


Any clues?
 
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My understanding is, and i may be wrong, every boat has osmosis. As soon as the hull sits in the water it will start to attract moisture.

The level is very dependant on conditions of the water, i.e Salinity, Temperature, length of time exposed.

I have osmosis on the rudder, but i'm not bothered.

As a Marine Surveyor friend of mine said "How many boats have been lost due to osmosis?"
 
I had very bad osmosis blistering on my previous boat, which I had very well treated. The improvement would, however, have been masked by the fact that I changed the engine for a lighter one and had a feathering prop fitted. Nevertheless the boat performed better and was significantly lighter for which some must be down to the replacement of water blisters with resin. When I bought the current boat it was surveyed by a very well qualified surveyor (bit of luck on my part). It also has clear gelcoat below the waterline. He detected osmotic wicking along the glas fibres in the hull, this being a precursor to osmotic blisters. He recommended that I should look at it when out of the water over the next few years. He did not consider that it was unreasonable that a boat of her age should be without such and was certain that it did not need immediate treatment. Result is I bought the boat with no reduction due to measured water content and am very, very happy with her.

If your boat has a higher water content as measured by his instrument (which is a device for measuring rising damp in houses) then all I would say is, "So what? When will it need to be treated and why? and all boats of yours boat's age will have a similar water content". Furthermore, "if you don't want to buy it because of the alleged water content of the hull then thank you for your interest and goodbye."

Sounds as if you have a bit of a Micky Mouse surveyor there, PM me if you want to canvass the opinion of a good one.
 
When I bought my boat 5 years ago, the broker let me see a survey of a few months earlier which said it had rampant Osmosis - written by a well known East Coast surveyor. I based my (very low) offer on that basis, and after having the offer accepted subject to survey, I then had two surveys done - one by another well known local 'practical' surveyor and another by my neighbour who had just passed his yacht surveyor exam. Both said that it didn't have rampant osmosis but did have a couple of small local 'wicking' areas. And to consider have it treated at some time in the future. Incidently the surveys from both were very similar except that my neighbour had added a lot of high quality photographs.
 
A well-known chief scientific adviser to the UK Government (Sir Solly Zuckerman, I think) was once asked how he had acquired his reputation for correctly predicting the likely success of novel projects. His answer, albeit tongue-in-cheek, went something along the lines: just by looking at the success of similar projects in the past - 99% of them fail; so, when asked for an opinion on any new beguilingly seductive scheme, I simply say it'll fail.

Think about it from the surveyor's point of view. He doesn't give a damn if the boat doesn't sell. If anything, he gives a cheer, because more unsold boats means more viewings, more surveys and, er, more beer. Failure of the sale implies that his client is relieved to have been given information that has stopped him from spending good money on a boat which to his now enlightened eyes is seriously flawed, albeit at the cost of a hefty survey fee. Alternatively, the sale may proceed, subject to a substantial price adjustment to allow for the cost of correcting the "defect".

From the seller's perspective, these are lose, lose alternatives; from the buyer's, lose, win; from the surveyor's, win, win.
 
Very much so, A surveyors paper is not worth the paper it is written on IMHO, I gladly accept that the views of the surveyor are well informed and with very good knowledge. If you look at what is written, everything is only ever possibilities....

And what is a hygrometer (sp sorry) calibrated with?

A dry piece of fibreglass
a mildly most piece of fibreglass
a damp piece ...... etc

It's a flawed techique and it can no better tell you wether osmosis will show up or not show up, it'll only seve to tell you wether your GRP is damp or not.... well thank you it has been in the water for 20 years :s

(p.s it is no slate at surveyors, i'm planning on becoming one :D )
 
Is it not correct that moisture content and osmotic blisters are two separate, though related, issues? My understanding is that moisture will always penetrate but that blisters only form if there are residual chemicals that draw sufficient water to cause pressure and consequent blistering. Hence, a hull can be wet but blisters may still not form.
 
A very porous gelcoat will allow fluid pressure to equalize with the outside and no blisters will form.Most old fiberglass hulls will suffer from water ingress and those with the most waterproof outer layers will blister.Sometimes blisters will form in the gelcoat only.
 
mortehoe said:
A certain N Wales almost-well-known-professional boat surveyor appointed for a buyer, scraped my hull 3 weeks ago, did a "moisture" test and declared the hull "very high" moisture reading = "Osmosis" was the predominant word that he said in his written survey report. ("non-laminar base-cellular-osmosis is probably present ..... etc ..." ..... Erghhh???????)

The same Surveyor did a report on the same boat 14 years ago and said the EXACTLY the same words affter making the same scrapes .....

.... the only difference was that the self same untreated hull neither had blisters then (1997) nor has blisters now.

How wide is his bog roll ????

So how can a blisterless hull have osmosis? Any clues?
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Not nearly enough information provided to form any meaningful comment.

What type / brand of moisture was used and on what setting.

Were readings taken at deck and top sides as well as below the waterline and what were they.

The fact that the surveyor 'scratched' the hull would indicate it was epoxy coated, is the case?

have you checked the internals of the hull at the point of test site to ensure it was not close to other structures like timber, tanks, bilge water or other.

Any one of the above could make a huge difference to the results.
 
Its likely a terminology issue more than anything else. To put it simply, osmosis is the process by which dilute solutions go through a semi permiable membrane to try and dilute more concentrated solutions on the other side. Semi permiable membrane is the gelcoat in your case. And if there is no where else for the solution inside the laminate to disperse to, then pressure builds up and bubbles or blisters form. But if there is somewhere else, then blisters might well not form.

So its quite possible to have osmosis and not to have blisters. Not only that but "wicking" ( the process by which water enters the laminate along the interface between a glass thread and the resin is also often called osmosis.

The blisters are cosmetic - you dont have any so your hull still looks pretty. The real structural issue is the hydrolysis of the laminate ie the breakdown. If you have ever seen it, the laminate goes like a sort of wet crumbly mess that you can scrape out with a finger nail. The "surveyors" who tell you that boats have never sunk because of osmosis are daft - if osmosis caused your boat to sink would you tell the insurance company who would then void the claim? In any case, there is likely another cause ie weakened hull hit by fishing boat.

It is however a pretty slow process in these temperatures and in salt water.

So you have a hull with a high moisture content and the surveyor is doing exactly what he should do and pointing this out to your buyer. So you might have to discount the boat a bit - but then you no doubt took advantage of his report to get a discount when you bought the boat. What goes around comes around.
 
Surveyors

I have some experience of these moisture meters, but more in construction where damp proofing companies use them to scare the sh** out of householders for great profit. They can get any result that suits them and it is amazing how even the big and 'reputable' companies use them. One of these UK wide companies reported several times in a matter of weeks when they were blitzing the area where we practised, we noticed that an identical set of readings for three different buildings. One building had CC tv and we got the owner to check it, the 'meter' never came out of the 'surveyor's' car. In every case the were finding dampness wher dampness was certain to be, for instance in stone walls or lime plaster.
If you are selling a boat make it clear to the broker or the buyer that you have no objection to surveys provided a complete duplicate copy of any report is provided to you, this massively inhibits exaggeration. No surveyor wants to write a report that says everything is A1, he has to find something to justify his fee. I always made an effort to be present when surveys were carried out if possible, it means you can see what they are up to.
 
I know of a yact where the purchaser's surveyor scraped about a dozen patches round the hull. There was a single small hole visible on one patch. There was a quote obtained for treatment of the "osmosis" The boat was blasted to reveal a perfect hull without even one blister or defect. It was quickly epoxy tarred and someone was £6K lighter.
 
Cerddinen said:
Is it not correct that moisture content and osmotic blisters are two separate, though related, issues? My understanding is that moisture will always penetrate but that blisters only form if there are residual chemicals that draw sufficient water to cause pressure and consequent blistering. Hence, a hull can be wet but blisters may still not form.
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That's generally true. The confusion is a matter of terminology. The dictionary definition of osmosis is " The passage of solvent molucules from a less concentrated to a more concentrated solution through a semi-permeable membrane". It's got B-All to do with blisters and is even the wrong term for the absorption of water by a hull. It's been commonly misused for so long however that it's meaning has been lost, and is one of those things you cant dissuade people from (like calling a Cutless bearing a Cutlass bearing)

The fact is that the normal polyester resin IS a semi permeable membrane and furthermore with large amounts of random laid CSM in some layers provides an ideal medium for water to be "wicked" through it. The majority of hand laid hulls are actually only 90 to 95% solids. There are inevitable air pockets that become quickly styrene rich bubbles. Some vacuum formed hulls (like the often criticised Bavarias) are better and can be as good as 98%. Some badly laid hulls are worse.

As salt water permeates through the hull (as it will) it takes salt with it in solution. I am not a chemist, but I believe the interaction between these salts and pockets of styrene (and a cocktail of other things I am sure) can cause a chemical reaction, and pressure to build up. This is particularly prevalent in the often CSM rich layer just beneath the gel-coat causing blisters, especially with a layup that was not too wonderful on the first place with lots of voids.

It is therefore of no real consequence that the hull has absorbed water although a poor laminate will absorb more than a good one. The question is, has that water caused blisters? Generally if not, it's not a problem and when ashore will dry out to some extent anyway.

Final word..... Moisture readings are notoriously misleading. The scales used to measure are comparitive, not absolute. The only meaningful result is the difference between the hull above the waterline and below....
 
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Surveyors and Osmosis

Sounds to me like a little it of knowledge being a dangerous thing. Ever since osmosis first became an issue on GRP boats there have been some surveyors who think they know all there is to know without doing any research and trying to understand it. (there are plenty, of course, who do try to understand and give an informed comment!).
If it's just irritating that you lost the sale I would put it down to experience. On the other hand if you want to do something about it I suggest you speak to Nigel Clegg at Passion for Paint. He's been involved into research into osmosis in GRP boats for 25 years, it's effects and how to deal with it. Now sells consultancy and supplies moisture meters among other things. There are a lot of accurate opinions above but Nigel knows more than pretty much anyone else.
 
Cerddinen said:
Is it not correct that moisture content and osmotic blisters are two separate, though related, issues? My understanding is that moisture will always penetrate but that blisters only form if there are residual chemicals that draw sufficient water to cause pressure and consequent blistering. Hence, a hull can be wet but blisters may still not form.
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There are two seperate issues but not the two you mention. There is blistering which is cosmetic only, and there is hydrolysis of the resin which is eventually structural. You can have hydrolysis without the blisters but not the other way round.
 
boatmike said:
It is therefore of no real consequence that the hull has absorbed water although a poor laminate will absorb more than a good one. The question is, has that water caused blisters? Generally if not, it's not a problem and when ashore will dry out to some extent anyway. .
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I dont believe that is correct Mike. BY their very chemical structure, polyester molecules are prone to breakdown in the presence of water which is why boatbuilders have moved on to vinyl resins and even epoxy. So a hull can deteriorate just through being wet, but it is a slow process unless there are laminating faults.

There used to be an article on the SP resins site about this but as with most British companies they have been sold out to a foreign multinational and I can't find it any longer.
 
Is The Chemical reaction Not Finite To The Void Products?

Having come to a similar conclusion as Boatmike when looking into my own vessel there is still one question which I have never really found the answer to.

If in my polyester lay up there are voids filled with resin products, then the chemical reaction would stop eventually when the compounds had used up the finite source of chemicals. However it is a fairly consistent claim that when this reaction starts (which can lead to blisters) it will continue. Why if there is only a finite pool of chemicals?

BosunHiggs has now raised a point that Polyester is prone to breakdown in water. Is this cured polyester resin, or uncured chemicals?

Will the chemical reaction which causes blisters or structural damage in a GRP layup happen if the Polyester resin has fully cured or does it only happen to uncured Polyester resin?

Its surprising that the industry (boats builders, trade associations, certifying authorities) have not come to a conclusion on this subject, or if they have that it is not widely known.
 
BlowingOldBoots said:
Having come to a similar conclusion as Boatmike when looking into my own vessel there is still one question which I have never really found the answer to.

If in my polyester lay up there are voids filled with resin products, then the chemical reaction would stop eventually when the compounds had used up the finite source of chemicals. However it is a fairly consistent claim that when this reaction starts (which can lead to blisters) it will continue. Why if there is only a finite pool of chemicals?

BosunHiggs has now raised a point that Polyester is prone to breakdown in water. Is this cured polyester resin, or uncured chemicals?

Will the chemical reaction which causes blisters or structural damage in a GRP layup happen if the Polyester resin has fully cured or does it only happen to uncured Polyester resin?

Its surprising that the industry (boats builders, trade associations, certifying authorities) have not come to a conclusion on this subject, or if they have that it is not widely known.
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I don't mean to start an argument and have already said that I am not a qualified chemist but the problem here is in oversimplification of a complex issue. Having been involved with many manufacturers of composite products and most material suppliers I have picked up quite a lot of incidental information and although I am only formally qualified as a Mechanical Engineer I have formed the following opinions.

Firstly lets kill this myth about resin types. Polyester, Vinylester, Acrylic and Epoxy resins have all been around for a long time. They all have benefits, but they can all potentially suffer similar problems arising from poor application. It's probably easier to list the things that have to be correct for a layup to reach maximum properties and longevity.
These are

1. Temperature (often poorly controlled)
2. Humidity (sometimes not controlled at all)
3. Stochiometry (ratio of resin to catalyst mainly)
4. Wetting out
5. Pot life
(if resins are used beyond their proper pot life they will never wet out the re-inforcement completely)
6. Consolidation. If done by hand can give variable results, entrap air and result in......
7. Variable resin to reinforcement ratios....

This is just a start.....

It's clear that even humble Polyester, if properly controlled will produce a fully cross-linked resin supporting the right reinforcement without too many voids. The adoption of Vinylester or any other resin will not improve quality or longevity over Polyester if Polyester is properly used. Vinylester will improve tensile, compressive, flexural and impact strength but voids in a vinyl boat will result in the same problems as voids in a poly one. Techniques of vacuum infusion (like SCRIMP), properly applied will give better results but Bosun Higgs IMHO is wrong to say Polyester breaks down in salt water. What causes ANY resin to fail is most usually the neglect to maintain proper control of all of the above. Some polyester hulls from the early 60s are still going strong and will continue to do so. Some Vinylester, Acrylic, and Epoxy lalups have failed. Please be assured that if you have a well built polyester hull it wont simply dissolve in salt water!
 
Nobody said it would dissolve but as I remember the article written by the chemists at SP , there is an issue with poly resin to do with a hydroxyl ion and which ensures that all poly laminated, however well consolidated, will get "osmosis" eventually. The physical manufacturing issues you list affect the speed greatly, but the chemistry of the resin is such that long term problems are unavoidable.

This is going from memory so I may be wrong. I will contact SP resins when they return to work.
 
Bosun Higgs said:
Nobody said it would dissolve but as I remember the article written by the chemists at SP , there is an issue with poly resin to do with a hydroxyl ion and which ensures that all poly laminated, however well consolidated, will get "osmosis" eventually. The physical manufacturing issues you list affect the speed greatly, but the chemistry of the resin is such that long term problems are unavoidable.

This is going from memory so I may be wrong. I will contact SP resins when they return to work.
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Well I would be interested in what they say, but as they are fundamentally an epoxy resin manufacturer they have a vested interest in "slagging off" polyester don't they?
As I said, I am not a chemist, and the chemistry of "cross linking" hydrogen atoms in a polymer is something I am not qualified to comment on. My opinion, for what it is worth, is based on practical application rather than chemical analysis. What I still believe is that polyester resin is chosen for two reasons. Firstly it is cheap and secondly, easy to use.
Vinylesters are now a lot cheaper then they were and almost as easy to use so many have gone that route to produce a better laminate in terms of physical properties, but there is little or no improvement in life over polyester if both are laid up properly. Acrylics are more expensive and more difficult but have many advantages, but are seldom used in boatbuilding. Epoxy is far superior in terms of properties, much more expensive, presents far greater difficulties in layup, is poisonous and is undoubtedly better in terms of permeability. Thats why we use it as a barrier coat. If we want a really high performance layup (like F1 car shells) we use carbon re-inforced epoxy resin pre-preg and cure in an autoclave. There is no doubt that for a boat this would (and does in the case of racing machines) produce a far better lighter, stronger laminate. It's just not economical for a production cruiser though. Talk of possible theoretical breakdown of polyesters over time is therefore not really useful unless figures are produced that support this theory. In other words, how long does it take for a properly laid up hull without defects to degrade in salt water of what temperature to what degree.... My own feeling seeing all those old 1960 Westerlys etc out there is .... A very long time!
 
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