Osmosis woes!

[Zagato]

I know this subject will have been done to death and it will bring nightmares to owners in the way an enquiry about rusty box sections would be to E-Type owners but I am thinking of purchasing my first yacht and would like to hear some real experiences/advice rather than salesman's reassuring patter!

My understanding so far is that osmosis to a certain degree will be inevitable in 1980's boats onwards and the best examples will be the ones that have been epoxy treated! I also read however that epoxy treating is now not thought to be a good idea as it traps the moisture and acidic chemicals within the hulls structure.

I suppose a boats hull is like a classic car - a hot potato that you need to buy in good shape and get rid off before major treatment is necessary. Have they got this problem sorted with new builds?

Thanks Chris

 

[Bosun Higgs]

It is believed that osmosis is inevitable in polyester boats but its incidence is effected by build quality and resin quality. So whilst you can never say a boat is osmosis proof, it is much more likely to be an issue in old boats than newer ones. Its also more likely in boats kept in warm water and in fresh water.

People will try to tell you that its purely cosmetic but it isnt. If you ever try to scrape out the hydrolysed laminate under a blister you will immediately know that.

The repair of osmosis involves epoxy resins which are much more waterproof but nothing is 100% waterproof. So a treated boat can blister again and is certainly not better than a boat that has never been treated and is blister free.

There are worse and more expensive boat problems than the pox. A new engine is usually more expensive than osmosis. And water in the deck laminate is far more difficult to deal with.

Boats are like houses and cars and wives. You cant expect to buy one and never have to spend money on it. So always keep some dosh back - never buy on credit and never spend all you have.,

 

[PCUK]

We are currently rebuilding a 1960 Seamaster (never mind why!!!) and there is no sign of osmosis anywhere even though it was full of rainwater for eight years!

 

[Quandary]

Starting seven threads in one day is an obvious sign of real enthusiasm, but might it not be a good idea to use the forums very effective search facilities first?
Doing this might help reduce the need to ask so many questions at once.

 

[Zagato]

Starting seven threads in one day is an obvious sign of real enthusiasm, but might it not be a good idea to use the forums very effective search facilities first?
Doing this might help reduce the need to ask so many questions at once.

Yes there is always the suggestion to use the search facility on common Issues and there are always the usual responses zzzzzzzz with the original thread topic going off course.

To put a new reason into the fold I have been pm'd by a few people responding to my questions with current up to date advice and contacts always very useful. Also some of the responses and all of the pm's I have received have been relevant to me personally with regard for instance to boat type or location. I now have good recommendations for boat type/ surveyer/ mooring and winter storage location. Thanks folks.

I would love to find the time to wade through all the old posts but new posts are more effective for me, forum users are happy to reply and others I am sure will be interested. If not, they wouldn't read the thread in the first place - no problem and hopefully back on topic

 

[Bobobolinsky]

It is believed that osmosis is inevitable in polyester boats but its incidence is effected by build quality and resin quality. So whilst you can never say a boat is osmosis proof, it is much more likely to be an issue in old boats than newer ones. Its also more likely in boats kept in warm water and in fresh water.

People will try to tell you that its purely cosmetic but it isnt. If you ever try to scrape out the hydrolysed laminate under a blister you will immediately know that.

The repair of osmosis involves epoxy resins which are much more waterproof but nothing is 100% waterproof. So a treated boat can blister again and is certainly not better than a boat that has never been treated and is blister free.

There are worse and more expensive boat problems than the pox. A new engine is usually more expensive than osmosis. And water in the deck laminate is far more difficult to deal with.

Boats are like houses and cars and wives. You cant expect to buy one and never have to spend money on it. So always keep some dosh back - never buy on credit and never spend all you have.,

Sorry I disagree with the statements that older boats are more likely to have osmosis problems. If as you say osmosis is a severe structural problem, then older boats suffering from it will be either gone to landfill, have been repaired, or the osmosis is so insignificant that it is only mentioned in surveys. I have seen osmosis ranging from a light rash on the wetted surfaces, to blisters the size of dinner plates. Older boats tend to be either full of it or completely free
I don't agree that osmosis is any more prevalent in fresh water than sea water, it is after all an osmotic process and as such, it is only the contact of the hull with water. I might admit that many freshwater boats are not antifouled and that may have something to do with it. I would like to know if there is any tie up between hand layup and chopper layup, but that is for another time.
I do agree that boats are big holes in the water in which to pour money.
What I can say is that of the older boats, those that were produced prior to the 1980's rash of mass produced boats are likely to have fared better than later boats and even boats three years old are not proof against it. It is a relatively simple fix to do for yourself. As pointed out a solid hull boat (of that age) is likely to be a better bet than a composite with balsa core and easier to fix

 

[SailBobSquarePants]

It's not the epoxy treatment per se..

It's not the epoxy treatment per se that is important, it is having the hull dried out through and through that determines the efficacy of an epoxy treatment. THAT requires getting all moisture barriers removed (old gelcoat, paint, previous epoxy treatments, etc.), and the judicious use of time, dry air, heat, and possibly vacuum suction to remove the moisture within the hull.

1) Some people strip the hull, skirt the boat in plastic, and let her sit for a few months, hoping that the ambient air will dry the hull out given time. This would work a lot better if England were not so naturally moist

2) Some people take the extra step and apply heaters under the skirting.

3) For the best result, you can take it to a Blakes-branded anti-osmosis facility, who will strip the hull and then apply vacuum suction "blankets" onto the hull, which heat the hull and suck the moisture out. This is not cheap, but it is much faster, and probably does the best job of removing all the old moisture. The nearest facility for that is in Chichester harbour, at the Hayling Island Yacht marina.

After each of these, the next step is to apply epoxy in 5 layers, totally sealing the hull. Do not use less, as the thickness of the layers is obviously what forms the moisture barrier.

Repaint with anti-foul, and launch her!

 

[Zagato]

I have recently read that you have to take back the damaged hull to sound material then flush/jet wash out the offending chemicals regularly over a few weeks then dry out the hull and treat. Apparently just drying out the hull is ineffective as the damaging chemicals are still left inside the hulls layers. I am not sure I could find the site again of the company that does this but will try Googling.

 

[keesvugts]

Osmosis

Although osmosis is the common name that people ascribe to the mechanism, what is happening is a breakdown of the polyester structure under the influence of water (hydrolysis). This will happen to a certain degree to all polyesters given enough time. All materials are to a certain degree permeable to water and as a result there is a flow of water molecules from the outside of the boat to the inside. This flow is very small and normally does not present a problem. However if there are voids in the material than there is a risk that a greater number of water molecules will accumulate and remain in that void. This means that locally there is a slightly greater rate of hydrolysis with the breakdown products accumulating in that void. The breakdown product are somewhat more aggressive than water and the process locally accelerates. If there are no channels from that void to the remainder of the hull this remains a local issue. However unreality there are likely to be a number of glass fibre strands penetrating that void. What happens next is that the boundary between the glass fibre and the polyester forms a channel that gradually increases in width and length as the breakdown process continuous until a new void is reached where the process repeats. As a result you are likely to find a spied web of white (dry) fibre strands interconnecting a number of blisters where there were voids or local areas of poor cure in the original material.
This process continuous relentless and is therefore not cosmetic as a number of fibres will connect to layers deeper in the lay up.
The deeper layers are likely to comprise rovings with long strands. This means that the mechanism can operate in these layers over a large area, possibly resulting in a reduction of interlayer strength or even deamination.
The process takes time and opiates generally from the outside inwards. This means that when the is is detected it is possible to remove the affected material until sound glass fibre is found. Typically this involves removing a relatively thin layer but this depends upon the construction of the layup and the time the process has been going on. Not removing this affected. Layer and just covering this with epoxy is a short time solution, the epoxy will not penetrate the affected areas and they will remain as voids, possibly still containing breakdown products. Hotvac or other methods don't really make much of a difference. Epoxy is less permeable to water but water will get in and the process will continue albeit under the epoxy and perhaps not visible for a while.
However if all the affected material is removed until sound clear glass fibre is reached the base from which to work is relatively sound. Also at this point you will find that the hull is dry because most of the affected material and breakdown products have been moved. (you can never remove all because there is always some deterioration throughout the material, nature will get it's way eventually). Once on sound material, all that is required is to ensure a good surface preparation and a build of of glass and epoxy to restore the original strength, followed by a good surface layer that has no fibres penetrating, a key layer and anti foul.

The process is simple and can be done by anyone with good diy skills. However it is very labour intensive and very dirty work. Typically on a 34 foot boat expect to invest some 1500 hours of labour and £5000 in materials.

There are no shortcuts I'm afraid despite many claims by the various companies offering osmosis repairs. Simply peeling the gell coat and applying a few layers of epoxy is a waste of money.

 

[Elessar]

Although osmosis is the common name that people ascribe to the mechanism, what is happening is a breakdown of the polyester structure under the influence of water (hydrolysis). This will happen to a certain degree to all polyesters given enough time. All materials are to a certain degree permeable to water and as a result there is a flow of water molecules from the outside of the boat to the inside. This flow is very small and normally does not present a problem. However if there are voids in the material than there is a risk that a greater number of water molecules will accumulate and remain in that void. This means that locally there is a slightly greater rate of hydrolysis with the breakdown products accumulating in that void. The breakdown product are somewhat more aggressive than water and the process locally accelerates. If there are no channels from that void to the remainder of the hull this remains a local issue. However unreality there are likely to be a number of glass fibre strands penetrating that void. What happens next is that the boundary between the glass fibre and the polyester forms a channel that gradually increases in width and length as the breakdown process continuous until a new void is reached where the process repeats. As a result you are likely to find a spied web of white (dry) fibre strands interconnecting a number of blisters where there were voids or local areas of poor cure in the original material.
This process continuous relentless and is therefore not cosmetic as a number of fibres will connect to layers deeper in the lay up.
The deeper layers are likely to comprise rovings with long strands. This means that the mechanism can operate in these layers over a large area, possibly resulting in a reduction of interlayer strength or even deamination.
The process takes time and opiates generally from the outside inwards. This means that when the is is detected it is possible to remove the affected material until sound glass fibre is found. Typically this involves removing a relatively thin layer but this depends upon the construction of the layup and the time the process has been going on. Not removing this affected. Layer and just covering this with epoxy is a short time solution, the epoxy will not penetrate the affected areas and they will remain as voids, possibly still containing breakdown products. Hotvac or other methods don't really make much of a difference. Epoxy is less permeable to water but water will get in and the process will continue albeit under the epoxy and perhaps not visible for a while.
However if all the affected material is removed until sound clear glass fibre is reached the base from which to work is relatively sound. Also at this point you will find that the hull is dry because most of the affected material and breakdown products have been moved. (you can never remove all because there is always some deterioration throughout the material, nature will get it's way eventually). Once on sound material, all that is required is to ensure a good surface preparation and a build of of glass and epoxy to restore the original strength, followed by a good surface layer that has no fibres penetrating, a key layer and anti foul.

The process is simple and can be done by anyone with good diy skills. However it is very labour intensive and very dirty work. Typically on a 34 foot boat expect to invest some 1500 hours of labour and £5000 in materials.

There are no shortcuts I'm afraid despite many claims by the various companies offering osmosis repairs. Simply peeling the gell coat and applying a few layers of epoxy is a waste of money.

A lot of this is true.

However 1500 hours of labour and £5000 materials is simply nonsense. £5k including the cost of labour is nearer the mark. A lot of it can be done DIY if you wish to mitigate the cost.

SOme facts:

A boat will start to absorb water form the day it's launched.

Epoxy is many many times more waterproof than gelcoat and will probably completely eliminate the effects of osmosis if applied before it starts.

"drying" a hull involves removing hydrolised solutes NOT water. Thus dehumidifiers do not help. They can temporarily reduce mositure readings but they will go back up again when the dehumidifiers are removed. Also they will not pass through gelcoat - only water will. So leaving the boat on the hard to let it "dry" is futile.

You "dry" a hull by removing the gelcoat and jetwashing it every day or even more often if you can. Counter intuitive maybe, but true.

If you epoxy coat a hull that has low moisture readings that have been artificially reduced by a dehumidifier or heat it will probably fail.

If osmosis has not started on your boat, and it starts quite a few years before you see the bubbles that people associate with osmosis, you are in my humble and very biased view, bonkers not to apply some form of epoxy to your hull.

________________

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[keesvugts]

I agree with what is said about water from day one and the drying by means of repeated pressure washing, this is part of the process but much more is involved to get a good repair. A sound repair for £5000 isn't possible.

Applying epoxy from new is a good suggestion but not a guarantee, I know this from personal experience.

1500 hours is what it takes from personal experience and the material cost must not be under estimated. You will use a lot of consumables and will need to invest in getting the right environment.

I agree that an experienced professional with the right tools will be able to do this in less time but not in 10% of the time. Even then you have already spent more than £5000 on labour alone.

Don't get me wrong, your boat will not be unsafe due to "osmosis" and any "largely cosmetic" repair may well give you piece of mind and may make the boat more sellable for a few years. This may make it the right thing for you to do but this does not constitute a repair.

In my view a repair should ensure that the original strength and stiffness of the laminate is restored and that the hydrolysis process is sufficiently arrested and slowed to maintain this status for at least 10 years.