Osmosis treatment - how long is it effective?

[bluedragon]

This question has probably been asked before and I doubt there is a definitive answer...but here goes anyway!!

I'm considering buying a 35 year old GRP yacht that had full below waterline epoxy treatment in the mid-80s (gel coat shot-blasted, dried, International Paints treatment applied, etc). From what I understand this was all done professionally and correctly. I'm told that mositure measurements over the years have been stable, and although not surveyed / inspected yet, I'm told there is no sign of blistering. I have no reason at this point to doubt any of these statements.

However, my question is whether treatment done 15+ years ago is likely to continue protecting the hull against osmosis for the forseeable future? I have another alternative purchase (same yacht / same era) that has just been done (with 5-year guarantee). This yacht has other issues I'd need to put right, but I'm wondering what "weight" to put on this new vs. old treament in my decision?

Many thanks.

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[oldsaltoz]

G'day Bluedragon,

Welcome to the forums, I'm sure will find all the answers you seek here, and perhaps contribute some of your own expertise and experiences to assist others.

When you get a moment, please put a little more info in your Bio, this will help when answering any questions, no personal stuff is required just general info.

As for your question re dated osmosis treatment; I think you need to consider the following.

The fact that the boat has no sign of blisters after almost 10 years indicates the original job was a good one (pending survey findings). If the survey indicates all is well expect another 7 to 10 years or more. With this mind you have to consider how long you plan to own this particular rig and what extras you plan to add and at what cost.

Then compare this to the second rig you have in mind and do the same maths for the same changes, repairs and so on.

Don't forget to check the rigging, mast and sail condition of each, this is often overlooked on older rigs and be a huge cost just a few years down the track, people tend to look at the condition of the engine and the finish on the outside more than anything else.

I hope this helps, perhaps you can tell us all later how you get on and what you based your decision on.

Avagoodweekend................



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[silverseal]

I understand that so called osmosis is a chemical reaction between water,salt and polyester resin, resulting in blisters. which contain a liquid which is essentially acetic acid, and has a characteristic smell. Further, well laid down gel coats, do not suffer from it. Halmatic in the 1960's put on two gel coats, and hence their hulls built then do not show the problem. Later practice of one gel coat, resulted in problems... But, if the epoxy replacement has been properly applied, and provided at waterproof skin, then osmosis should not occur. As Lloyds approve hull building, and for that matter certain rectification to hulls, I would speak to their technical department. I would also speak to West, as their resins are used to replace stripped off polyester gelcoats, and they have 20+ years experience and could more accurately answer your question. Finally, how many boats have sunk due to osmosis? - I suspect less than 1

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[discoduck]

Hi
Who did the most recent treatment.Then ask them what moisture level they got down to. You are looking for 5 % or less. Secondly when they skimmed off the the gel coat and dried out the hull. Did they then put a layer of fibre glass before appling the epoxy.
With the older boat treatment you have only one choice. That is to pull it out of the water and let the hull dry out for a few fine days and do moisture checks around the hull. Looking for blisters is not a good check.
The boat I puchased did not show blisters as such ,but slightly darker patches. But when we applied the moistue meter all was revealed. Wet very wet. You can contact me at discoduckmb@yahoo.com

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[Birdseye]

All polyester laminates are prone to osmosis - its inherent in the molecular chemistry of the resin. However, its fair to say that well consolidated laminates are much more resistant than poorly consolidated one. Which is why you can get osmosis on one side of a boat where one laminator has worked, and not on the other where a more consientious laminator has worked.

Coating with epoxy after careful preparation limits the water getting to the laminate and therefore any future problems. But epoxy is not totally impervious to water, and the amount of water penetration through the epoxy depends on coating thickness, and time, and other issues.

So on the older boat you have a poly laminate of unknown quality covered by an equally unknown epoxy coat. No one can tell you how long it will last. But even if you buy an almost new uncoated poly boat, no one can tell you how long before you get a problem.

Look on osmosis as you would on rot in a wooden boat. A GRP hull is not totally maintenance free, you might be unlucky and have to do an osmosis job. But its not the end of the world, its not terminal, it is something you can do yourself. Its simply one of the inevitable major maintenance jobs like re-engining.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[jonjo]

Re: 50/50

Speaking as someone who viewed many old yachts and purchased on old problematic 38ft yacht before buying new, I would say it’s a toss up when valuing 2 yachts with the backgrounds you describe.

The failure rate of osmosis jobs is quite high in the 5 to 10 year timeframe so a job that is stable at 15 years is a distinct plus point. Maybe the hull is well constructed but 15 years ago the owner over reacted to a few blisters?

Don't cogitate in silence over this dilemma, I found that surveyors are prepared to pass by a yacht and check out a specific issue for quite a low fee particularly if this leads onto a full survey instruction.

Remember you are holding the chequebook and control the whole situation. Click you fingers at owners and the marine industry and say "I WANT".

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