Osmosis - when to worry about it?

[SimonA]

My 32 year old boat has some blisters about the size of a 50p. I have 4 or 5 near the bow and several more underneath the hull. I burst one and it was full of liquid.

As most boats of that age are likely to have blisters I'm sure it's nothing to worry about. But I was wondering at what point you should start to worry.

 

[ValleyForge]

As others have said before, a boat has never sunk due to the big 'O'. Realistically however the sale value of your craft is probably 50% & less of what it might otherwise be.

 

[Bandit]

Valley Forge's prediction is a little drastic.

Boats dont sink because of osmosis.

Most old hulls have a bit of it.

When you cracked the blister did it smell of chip shop vinegar ?

If your not looking to sell the boat in the near future just keep an eye on them.

If you are intending to sell the boat in the next year or so get them sorted.

 

[No Regrets]

Osmosis is present in just about every GRP hull, and ongoing, in the same way as corrosion in steel vessels.

Blisters should be treated on an annual or biannual basis as required, as basic maintenance, so I'm told, and the cost budgeted for as a normal running cost.

I trust thats a reaonable way of looking at things?

 

[Grajan]

GRP Boats can and do sink because of osmosis/hydrolosis but we are talking palm size blisters and chopped strand mat visible!The biggest worry is the weakening of the laminate causing appendages to fall off or out! Localised repair would be, grind off blisters and dry out, then fill with Epoxy fillers to manufacturers reccommendations
If the blisters are deep I would laminate some layers of glass tape into the blister crater overlapping each layer that is applied then fill and fair, prime then antifoul

 

[Tranona]

Grajan. Where is your evidence that boats "can and do sink because of osmosis/hydrolysis"? I have never seen any mention of this in all the learned or journalistic publications on the subject. Usually the advice given is exactly the opposite - osmosis does not result in holes in the hull that would cause it to sink.

Would welcome details of any examples that disprove this.

 

[burgundyben]

Have a read of Tony Staton Bevan's book on the subject, I'm not aware of any sinkings but serious structural weaknesses are possible and should be addressed.

Head in the sand is not an apporpriate.

 

[Grajan]

As I said in my post the problem is the weakening of the hull causing either splits in the hull ,not physical holes, keels falling off or shroud plates pulling out
The vessels that I have been involved with that came to grief
were recovered and repaired and are, I believe, still in use all barr one and very fortunately no lives have been lost that I know of
These vessels ranged from a 40' Naval craft split from keel runner to gunwhale, bilge keelers that have lost a keel , a fin keeler where the keel split and the concrete ballast fell out, a 18' motor boat that literally opened up like a kipper! these are boats that I have been involved in the recovery and the repair of, all be it a good few years ago.
I spent the majority of my working life visiting yards throughout the UK consequently I heard of other sinkings and viewed numerous other yachts/craft where sections of hull had to be cut out and new sections laminated in due to lack of strength within the laminate caused by the expansion pressures tearing the laminate apart
For chapter and verse on the subject read what Nigel Clegg has to say about Osmosis/Hydrolysis

 

[dombuckley]

At the moment, you have nothing to worry about: all your blistering is between the gelcoat and the lay-up, so not actually affecting structural strength. The gelcoat, after all, is only a cosmetic surface. The time to worry is when you are getting blisters about saucer-size, which are hard and cannot be punctured, this is an indication that delamination is occuring within the lay-up itself, which is inevitably of structual significance.

 

[burgundyben]

Without opening a blister and looking at the condition of the laminate underneath I dont think you or anyone else is able to say that there is nothing to worry about.

At 32 years old the boat in question will have been laid up using CSM bound with PVA, its well known that this is more susceptible to ingress of moisture and weakening of the laminate than later GRP laid up with CSM bound with polyester.

The correct course of action (which should be taken by any boat owner being prudent about the condition and maintenance of his boat) would be to find an experience surveyor and ask him to look at the matter.

I'm quite sure the surveyor would open a blister up and poke about the laminate underneath, I pretty sure he wont shurg his shoulders, declare its ok and wander off.

Relying on the opinions of a load of boat geeks on a internet forum does not equal proffessional advice or a strategy for maintaining GRP boats.

But what do I know, nmine are all wood.

 

[PCUK]

Ben, your getting hysterical now, so stop it /forums/images/graemlins/grin.gif
Osmosis isn't the black death of boats, as described here it is simply minor and basically cosmetic repair work.
If the simple repairs are made now there is plenty of time in the future to monitor further deterioration if it occurs.
Drying the boat out for a few monnths each winter is one of the best ways of avoiding any future problems.
Osmosis is not the reason I have a steel boat! /forums/images/graemlins/cool.gif

 

[burgundyben]

A very high percentage of cases are cosmetic, however, when osmosis has been present for a long time significant weakening of the strucutre can occur.

No hysteria on my part, get proffessional advice, that all. /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif

 

[Bajansailor]

Ummmm, Ben, isn't PVA a release agent used (in addition to wax) to ensure that the mould and the moulding part company amicably?

The earlier fibreglass boats were invariably laid up with predominantly CSM using orthothalic (sp?) polyester resin - later on isothalic resins were used which apparently have better resistance to osmosis. And vinylester resins are now all the rage.

 

[burgundyben]

Release agents are generally wax based as you say, the last hull I helped lay up (sometime in the late 80's) it was all the rage to use a McGuire's wax.

Some moulds have provision to pump compressed air in between the mould and the hull to help push it out.

PVA was the bonding agent used to hold the strands of glass together in the CSM so it could be handled in a sheet form, without a bonding agent you just have a big pile of little strands!

Later on the PVA was switched for polyester.

It known that PVA CSM is more prone to moisture ingress than later polyester based.

I'm a bit behind on current resin technolgy, but you are right, the switch from ortho to iso resins was made quite a while ago.

Damage to GRP structures could be due to air pockets, poor catalisation, poor workmanship, mechanical damage, incorrect curing times and temps etc, not just the long term ingress of moisture, in most cases its not much to worry about, but I feel that in all cases it should be looked at by a suitable knowledgeable person and action taken accordingly.

Maybe I have a chip on my shoulder cos I'm a wooden boat man! /forums/images/graemlins/smile.gif

 

[ValleyForge]

I think I will stand by my earlier comment - but modified to say
'Very few boats have sunk due to .....'

A craft affected with large weeping osmosis blisters is inevitably going to be considerably less valuable than one which is not. A survey will confirm this.

Motto - get it fixed, not bodged.

 

[AdeOlly]

Drying the boat out each winter will unfortunately have little effect once blisters start appearing as the hydrolised chemicals behind the gelcoat will not dry out; as soon as the boat is relaunched the osmotic process resumes. See here for a good guide to the stages of osmosis and what works when.

 

[Tranona]

Grajan, sorry to come back on this, but how many of the failures you have seen are caused directly by osmosis. I have no doubt there have been structural failures in GRP as I have seen them myself, but not caused by osmosis (that is the blisters, pockets etc), even though it was probably present in the laminate. The sort of failures you describe are usually due to poor design, poor workmanship or mechanical failures.

I remember the 1987 storm and the consequences because my wooden boat was damaged when it dragged its mooring. The surveyor commended me for choosing a wooden boat based on what he had dealt with in GRP boats where damage was almost always hidden and only obvious for example when a bulkhead cracked or a chain plate pulled out, or laminated floors and frames pulled away from the hull.

Back to the original post - what does one do about it if your boat has blisters? Not ignore it, recognise that at some point some remedial work is required. Even the "experts" do not agree on the remedies, but the latest hot vac process seems to be logical if the blisters are wide spread to the point where the gel coat needs replacing. Nigel Clegg covered this well in his articles in PBO last year.

 

[Nautical]

My thoughts were and had been for a long time osmosis was a big turn off value wise and that it was some kiss of death then I started looking at hatteras yachts some of the strongest boats ever built. The advise we received is that nearly all of them after a few years have osmosis in fact one article commented that Hatteras should have take out a patent on boats with osmosis, then the good news came that in 95% of cases its generally superficial and regular maintenance keeps it in check and some of the early ones are now 35 years old and still going strong, having said that the hulls were up to an inch thick whether a modern moulding is up to that sort of abuse i couldn't say, nevertheless past a certain age nearly all boats have it to some degree. best get a professional to check it out and a report, listening to assumptions here is like stirring hot tea with a chocolate biscuit, bit like untreated osmosis......bound to turn to soggy mush after the fact /forums/images/graemlins/grin.gif