Osmosis Advice please

I am about to buy my first boat 29ft, 1982 my dream boat an I am in Love! The price is right but the survey which was done when the boat was taken out of the water suggests osmosis may be a problem in the future. The boat has now been out of the water for 8 months so she had dried out I have had two conflicting suggestions re my problem.

One suggests I leave it put the boat back in the water enjoy my sailing and sort out the Osmosis when it appears ,on the basis that any 20 year old boat will have it one day

The other says I should have epoxy treatment NOW while she is dry this will prevent Osmosis for up to 15 years.

Could some of you old hands please give me some advice what would you do.

Thanks James

Who told you that a dried out boat on the hard would be susceptible to the dreaded misnomer 'osmosis'? (My boat a Jeremy Rogers 1968 is as sound as sound can be - she surveyed every year and the moisture meter still reads reads zero)

'Osmosis' in GRP is stagnat water getting into the voids and hydrolising it creating 'vinegar' plus expansion.

The boat that you want has a price. If the AYMSDA Surveyor of your choice says that it has a potential Osmisis problem, then all you've got to do is to get a quote for slurry blasting and re-epoxying. Deduct this plus 10% from your offer which should be at least 20% less than the asking price if you are going through a broker ...

NigeCh (RogueWave Inc)

*

Dont worry about it. From what you say it sounds as if the Surveyor is just covering his ass. Go for it and happy sailing.

There is no guarantee that, even after 8 months out of the water, she is dry enough to treat.

If she has no osmosis (or whatever you care to call it, boat pox is as good as any in my view - scientifically speaking it is not osmosis)she is unlikely to develope it to a sufficiently serious degree to require immediate action for afew years. If you do treat it now, you won't get a guarantee of more than five years, maybe only three, from the people who do the job, so you could be just throwing money away. Pox treatment may last for 15 years but, as I found to someone elses cost, it can also last just two years.

In my view, and this is slightly controversial, if your boat gets pox in, say three years, I would not bother with treatment for at least another three or four years while monitoring its progress carefully. Indeed, unless it got very advanced, I would leave it until the boat came to be sold then price her to allow for the new owner to do the job if he wished. It is extremely rare for pox to be so bad as to threaten the structural strength of a hull boat.

Most boats of this age will have absorbed water moisture. A couple of hundred pounds weight is not uncommon in a 30'. I'm afraid that this is a fact of life which should be allowed for.

However, water moisture absorption does not lead to osmotic blistering (as NigelCh says) - the causes of which are not clearly understood - instead it could be Polyester Hydrolysis or even water accumulating in voids in an inert manor (like water in a sponge).

Has the anti-fouling paint been stripped off and the boat stored undercover?

If not, I doubt (esp with the amount of rainfall we have had recently) that the hull will have been dried sufficiently during the past 8 months.

If you buy the boat, either get the antifoul blasted off and leave it for 3 months over the summer and then have preventative epoxy paint treatment or sail it over the summer and then get it dried properly over the winter.

Of course it could be the surveyor covering his back...

On what you have told us you do not have osmosis - yet; this would be visible. You have a surveyor who, like many in the profession, has proabably looked at the age of the boat and advised you to take care; reasonable enough. But is this a direct call to action?

Clearing off the hull and applying 5 coasts of 2 pot is no small undertaking, but you will feel better having done it, any future purchaser will be somewhat reassured, and any moisture in the hull will likely not increase as much as if you took no action and sailed on. This is what I did; and 8 years later the boat sold easily and without suveyor caution, because there was no deterioration.

I suggest you do not take a dismal view of your prospects at this stage - you appear not to have grounds for such.

Peter Gibbs

Found a site that appears to be give practical advice on osmosis and surveying. www.turbolink.co.uk and look for the marine survey page. Brian Jessop

I take it you've asked your surveyor to tell you exactly what he means by "may be", "problem", and "in the future". He's an engineer of sorts. Should be able to put some ballpark numbers in there. If he has no evidence, he should say so. If the boat is from a builder with a bad reputation for this, he should tell you. Blistering problems mainly arise from poor control at the manufacturing stage and hulls which have been moulded in properly controlled conditions seldom suffer. Even where problems exist, the action required is, I believe, seldom as drastic as the fixers would sometimes suggest. Whatever you do, absolutely do not use a solvent based epoxy as a preventative barrier. The previous owners of my boat did this and got away with it. According to my surveyor, had there been an incipient problem there, they would have had a major disaster on their hands; whereas - hope it works this way! - I got a boat that's been tested to the edge AND has an impermeable barrier. Certainly, 12 years on I've no signs of blistering in a 22 year old boat.

"If the boat is from a builder with a bad reputation"

So who are the builders who should be avoided and, on the other hand, those with a quality record when it comes to this osmosis stuff???

Don't know whether the site can stand a "name and shame" thread. Doubt it. On the other hand.... A few years ago, I read a review of the old Princess 32 motor cruiser from which a comment stuck in my mind that osmosis was virtually unknown in them or other boats from the same stable, the stable being Marine Projects in Plymouth. Since the mid-70s, almost all Moodys and Sigmas, and goodness knows what else, came from this builder. I'll vouch for one Marine Projects Moody from 1979 showing no symptoms: haven't a clue about the rest, other than I've heard no complaints.

Talk to Paul Hockey on Symblast site and have a look at www.yachtsurvey.com - this is an excellent American site which amongst many other topics covers blistering. They do not call it osmosis. In your position I would bight the bullet and slurry blast and epoxy if only for peace of mind and to make a future sale potentially easier.

[Terence Davey]

I am about to buy my first boat 29ft, 1982 my dream boat an I am in Love! The price is right but the survey which was done when the boat was taken out of the water suggests osmosis may be a problem in the future. The boat has now been out of the water for 8 months so she had dried out I have had two conflicting suggestions re my problem.

One suggests I leave it put the boat back in the water enjoy my sailing and sort out the Osmosis when it appears ,on the basis that any 20 year old boat will have it one day

The other says I should have epoxy treatment NOW while she is dry this will prevent Osmosis for up to 15 years.

Could some of you old hands please give me some advice what would you do.

Thanks James

From Terence Davey
I have read the many replies to the above posting and am astonished to discover the subject of osomosis in polyester-glass mouldings remains the subject of so many myths and so much ignorance.

1. So called osmosis is no more than the slow decomposition of the materials of the moulding through instability. This may be speeded up by the presence of moisture, floating in warm water or the unusally high number of the tiny voids that are always present in g.r.p.!


2. Excluding the presence of moisture from the moulding is not only impossible, but effective desiccation (also impossible) would not arrest the decomposing reactions in g.r.p when the decay has become significant.

3. Polyester of even the simplest formulation is when effectively cured, very stable, resistant to acid and likely to have an indefinite service life if it is not stressed unfairly by poor design or unfair usage.

4. The reasons for instability of cured mouldings are beyond numbering but the most common are poor formulations, errors in mixing and low temperatures during the cure.

5. Most peel and paint treatments are merely cosmetic and the high strength-high build paint films slow the reaction for a while and also prevent the pressure of the decomposition from being apparent.

Conclusion: If you have a sound but blistered boat use it and be happy, but accept it may have a slightly lower resale value.
If the structural integrity of the boat is likely to be compromised by the decay, then it should be radically peeled and the remaining sound material (assuming there is any) can be used as a base for reconstruction using epoxy-glass.

TD

[GrahamM376]

Sounds like the surveyor is covering his backside, either it has or hasn't got osmosis. Many older boats will get it (my Centaur and Berwick both had) but it's not the end of the world and treatment is within the capabilities of most DIY owners anyway.

If the hull has been dried out for 8 months and has low moisture content with no blisters, it may be worth DIY epoxy treatment now which would slow down moisture absorption over the next few years.

[Racecruiser]

Probably worth telling the forum what the moisture readings are - if high I would suggest caution.

[fireball]

you're picking a 10 year old thread up and commenting as though it is current thoughts ...

Seems to be a trend recently ...

[Terence Davey]

Sounds like the surveyor is covering his backside, either it has or hasn't got osmosis. Many older boats will get it (my Centaur and Berwick both had) but it's not the end of the world and treatment is within the capabilities of most DIY owners anyway.

If the hull has been dried out for 8 months and has low moisture content with no blisters, it may be worth DIY epoxy treatment now which would slow down moisture absorption over the next few years.


DIY epoxy treatment can make blisters far more obvious and more corrosive. If your boat is not blistered or appreciaby weakened. Leave it alone.
Osmosis is not a matter of 'have it or not'. Hull blister symptoms are not anything to do with osmosis.
Yes, epoxy coatings do slow down the rate of moisture adsorption.
Most so called osmosis claims are degenerative reactions in gelcoat and superficial erosion of the 'skin out' laminate by acidic blister fluids.
Effectively permanant repairs can be made by peeling off the gel and damaged 'skin out', removing the residues of decomposition by steam cleaning or heat in vacuum, then recoating after replacing the skin out laminate with epoxy-glass.
Unfortunately, it is not unusual for a surveyor to diagnose 'osmosis' and then tell the buyer that the boat will be OK after it has had an 'osmosis treatment'.
That has been the ruin of many and especially, the boatyards who guarantee such repairs.
Decomposing hull mouldings can only be detected by intrusive testing. That is: core sampling or cone shaped drillings.
If a boat is found to be so affected when it is peeled, then the cost of repair (given that a repair is possible) may be more than the value of the boat.

TD

[Terence Davey]

you're picking a 10 year old thread up and commenting as though it is current thoughts ...

Seems to be a trend recently ...

Thanks, but these threads come top of the search list when people look for "osmosis advice" and there should be some informed opinion that is up to date. I hope I have provided it, even though it is at the end of a string of not very helpful comments.

[minkysailing]

Thanks, but these threads come top of the search list when people look for "osmosis advice" and there should be some informed opinion that is up to date. I hope I have provided it, even though it is at the end of a string of not very helpful comments.

Why do I get the feeling that someone is using a 10 year old thread to promote themselves...!!!

[Terence Davey]

Why do I get the feeling that someone is using a 10 year old thread to promote themselves...!!!

The thread although ten years old; is top of the Google search for 'osmosis information' in the UK, that is why I have commented.
If you know anything about 'osmosis' you will also know that my reputation needs no promotion.
I would like to share my knowledge and experience of the subject with people who are anxious about their boat problems. There appears to be many of them and few professionals without vested interests.
Whoever you are, you appear to mistake my motive because I do not hide behind an alias.
TD

[andrewbroadbent]

From Terence Davey
1. So called osmosis is no more than the slow decomposition of the materials of the moulding through instability. This may be speeded up by the presence of moisture, floating in warm water or the unusally high number of the tiny voids that are always present in g.r.p.!

TD

This is not my understanding of Osmosis.

From Wikapedia:
"Osmosis is the movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides."

As this relates to GRP boats, the solvent is water, and the selectively permeable membrane is the gelcoat. The solute is glycol, which used to be included in the resin mix as a solvent. Glycol is hygroscopic (will attract and dissolve in water), and therefore if present in your hull will cause water to diffuse by osmosis through the gelcoat. This influx of water causes blisters to form, and can cause the GRP to start to break down. Therefore any disintegration / decomposition would be as a consequence of osmosis, but not osmosis itself. The glycol will also break down to acetic acid (vinegar) in the presence of water, therefore you often get a vinegar smell when you burst the blisters.

If a boat has bad osmosis, the "cure" as I understand it involves peeling off the gelcoat, and then washing out the glycol from the GRP, using lots of fresh, preferably hot water, before drying thoroughly. Note that the washing stage is essential, just drying the hull will leave most of glycol behind. The hull can then be made good and re-coated. This is usually done with epoxy, as epoxy has a much lower permeability than gelcoat and thus the rate at which water can diffuse through epoxy is a lot less. In theory, if you have removed all the glycol, you could re-coat with gelcoat and not get any further problems, but epoxy is preferred.

I would agree with your comments that boats not displaying significant symptoms do not need treating, and some surveyors may well try and cover their backsides, when moisture meter readings are high.

I don't see any problems with small blisters being ground out, cleaned with fresh water, dried, and filled with epoxy filler on a DIY basis. If the boat suffers further osmosis in the region of the repair, then further work would obviously be required but I cannot see how this type of repair would make the blisters "more corrosive".

[Terence Davey]

This is not my understanding of Osmosis.

From Wikapedia:
"Osmosis is the movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides."

As this relates to GRP boats, the solvent is water, and the selectively permeable membrane is the gelcoat. The solute is glycol, which used to be included in the resin mix as a solvent. Glycol is hygroscopic (will attract and dissolve in water), and therefore if present in your hull will cause water to diffuse by osmosis through the gelcoat. This influx of water causes blisters to form, and can cause the GRP to start to break down. Therefore any disintegration / decomposition would be as a consequence of osmosis, but not osmosis itself. The glycol will also break down to acetic acid (vinegar) in the presence of water, therefore you often get a vinegar smell when you burst the blisters.

If a boat has bad osmosis, the "cure" as I understand it involves peeling off the gelcoat, and then washing out the glycol from the GRP, using lots of fresh, preferably hot water, before drying thoroughly. Note that the washing stage is essential, just drying the hull will leave most of glycol behind. The hull can then be made good and re-coated. This is usually done with epoxy, as epoxy has a much lower permeability than gelcoat and thus the rate at which water can diffuse through epoxy is a lot less. In theory, if you have removed all the glycol, you could re-coat with gelcoat and not get any further problems, but epoxy is preferred.

I would agree with your comments that boats not displaying significant symptoms do not need treating, and some surveyors may well try and cover their backsides, when moisture meter readings are high.

I don't see any problems with small blisters being ground out, cleaned with fresh water, dried, and filled with epoxy filler on a DIY basis. If the boat suffers further osmosis in the region of the repair, then further work would obviously be required but I cannot see how this type of repair would make the blisters "more corrosive".

Yes Andy,

I agree with the definition of of osmosis. However if large semi-permeable membranes were so easily produced as a shell of gelcoat, then the world's drinking water problems would be solved. Gelcoat is simply 'permeable'. Water molecules pass through it, somtimes as much as a gram a square metre every 24 hours.
The acidic residues you speak of are usually the breakdown products of the reactive diluent styrene with around 1% of it propylene glycol. There is always an excess and it slowly decays and evaporates. Except that is, the amounts that are trapped in the fibres and globular bubbles that are present in all mouldings.
This is a simplification though there is a well known and easily understandable explanation for the problem from the simple blistering of gel right through to the resin mass reverting to sticky toffee. I had been inclined to post as much as possible but find my presence here resented.

Seal in acidic residues and like the moisture in hollow rudders, it will be push up blisters and cause erosion etching of the skin out laminate that gives the leopard like spots on peeled boats. Broken blisters are harmless.
TD

[lenseman]

The following is all you need to know about fibreglass boats and osmosis:

"There are only three kinds of fibreglass boats. Those that have blisters; those that had blisters and those that will have blisters."


;)

[Boo2]

I agree with the definition of of osmosis. However if large semi-permeable membranes were so easily produced as a shell of gelcoat, then the world's drinking water problems would be solved. Gelcoat is simply 'permeable'. Water molecules pass through it, somtimes as much as a gram a square metre every 24 hours.

No, the gelcoat is semi-permeable :

As you correctly say, water passes through the gelcoat but the solute in the layup cannot so the pressure in the voids builds up resulting in a blister. This is plainly osmosis at work and I really do not understand at all why there is a tendency to say that the word "osmosis" is not applicable here : it's a very simple application of its definition.

Boo2

[johnjfrake]

I am reminded of comments the two very reputable south coast surveyors have made to me during the course of business (I was the buyer), " No Boat ever sank due to osmosis". I suggest you get your surveyor to state whether there are any current or potential(next 2-3 years) structural weakness in the hull and if not get on and sail her, if so then get something done about it and get the vendor to meet most or all of the costs! If the vendor won't then walk away, your heart may be broken but your wallet will remain intact and you will sooner or later find another boat that you will love just as much!

regards


johnyjf

[Terence Davey]

No, the gelcoat is semi-permeable :

As you correctly say, water passes through the gelcoat but the solute in the layup cannot so the pressure in the voids builds up resulting in a blister. This is plainly osmosis at work and I really do not understand at all why there is a tendency to say that the word "osmosis" is not applicable here : it's a very simple application of its definition.

Boo2

So it appears, but the pressure comes from gas and residues from the decomposition of the materials and not osmotic pressure resulting from different densities across a semi-permable membrane.

The argument confuses and alarms boat owners then then gives respectability to an industry that often 'repairs' blistered boats that are perfectly sound.
Using the word osmosis as the name for the decomposition of the resin in g.r.p. mouldings is crazy. Hulls do fail and founder through softening of the composite, poor adhesion of laminates and other reasons associated with failure to be sure that the resin is the hard, glassy and effectively inert material that it is supposed to be.
You can't exclude the existance of this problem in a hull by the use of a moisture meter. Such a meters can help, but they are only aids.
As I said, hulls diagnosed as 'needing an osmosis treatment' can be found after peeling to be in need of radical repairs that can exceed the value of the boat.

TD

[maxi]

"Guest" has it just about right.

My current (1977) boat's initial survey stated that "some pre-osmotic blistering is evident" - Having myself already surveyed the boat finding NO osmosis but, my insurers would not accept a self-survey. I subsequently gave the surveyor the option of paying for the boat to be re-lifted and scrubbed, plus showing myself & 2nd witness irrefutable evidence of osmosis or, of returning his fee and the costs incurred by me in lifting and scrubbing. He chose the latter with some alacrity.

Now some 15 years later, and with very few periods out of the water, the boat still shows no sign of osmosis nor of elevated moisture content (which are by no means the same thing).

You seem to have chosen a surveyor who is a long way short of the mark.

[nimbusgb]

keeping up the 10 year old thread revival

Osmosis is a bit like iPad ...... a fad that all and sundry are climbing on to.

More hype than substance!