Blisters! Is it Osmosis?

[buchananD]

It is worth doing it and if it shows up as being dry then prevention via epoxy coating might be the way fwd.

Nick in response to your replay if I may: osmosis occurs as a result of contaminants in the laminate not the gel coat. The gel coat simply gives it away with the tell tale signs being blisters. Local treatment like that proposed will never remove the contaminants nor does widespread grinding alone because just how deep do you go? Hotvac seems to be one of only a couple of more effective techniques that minimises the loss of laminate whilst extracting most contaminants and drying the hull at the same time. Here we are looking, it seems, at a very local issue (subject to moisture meter readings) but you can't be absolutely sure so if you treat these local blisters as suggested and keep a watching brief on the hull over the next couple of seasons you can then decide whether to put an epoxy coating on but if doing so the hull needs to be dry. As previously mentioned the problem with resealing these blisters with epoxy is that because the contaminants have not been removed (grinding out won't remove them) if you seal them up the concentrations will increase and make matters worse. Already repeating my self so I'll leave it there - good luck Spepetus!

[s/v Jedi]

Originally Posted by buchananD

Nick in response to your replay if I may: osmosis occurs as a result of contaminants in the laminate not the gel coat.

I'm sure that can happen but all the cases I have seen have the void/contaminants between the gelcoat and the laminate... right at/in the fiberglass mat that most builders put between to prevent print-through from bulkheads etc. into the gelcoat. It is that mat material that's most often the source and it is not considered part of the structural laminate.

In my case I have a layer of resin with chopped strands (chopper gun) that is the source. The laminate itself is underneath and untouched.

But this is why I wrote to investigate on a blister... slowly grind to find the source and find out if it's in the laminate or not.

ciao!
Nick.

[osirissail]

Mr Bengt Bloomberg may have written the "bible" on blisters in Northern Europe/Sweden, but his ideas are contrary to decades of research and documentation on the subject over on this side of the Atlantic. Some of his statements are downright outrageous. We have different "bibles" that govern what we do over here to repair osmotic blisters.
- - What works for boats made in Sweden or Northern Europe is probably quite different from boats made in the USA/North America. Different manufacturers of resins and formulations and boat hull lay-up create different problems, causes and cures. - - Different strokes for different boats.

[minaret]

Originally Posted by buchananD

It is worth doing it and if it shows up as being dry then prevention via epoxy coating might be the way fwd.

Nick in response to your replay if I may: osmosis occurs as a result of contaminants in the laminate not the gel coat. The gel coat simply gives it away with the tell tale signs being blisters. Local treatment like that proposed will never remove the contaminants nor does widespread grinding alone because just how deep do you go? Hotvac seems to be one of only a couple of more effective techniques that minimises the loss of laminate whilst extracting most contaminants and drying the hull at the same time. Here we are looking, it seems, at a very local issue (subject to moisture meter readings) but you can't be absolutely sure so if you treat these local blisters as suggested and keep a watching brief on the hull over the next couple of seasons you can then decide whether to put an epoxy coating on but if doing so the hull needs to be dry. As previously mentioned the problem with resealing these blisters with epoxy is that because the contaminants have not been removed (grinding out won't remove them) if you seal them up the concentrations will increase and make matters worse. Already repeating my self so I'll leave it there - good luck Spepetus!

Nice someone familiar with the hotvac. We were the first yard on the west coast to acquire one, at great expense, and ended up actually being the guinea pig for their R&D department as far as we could tell. Despite a lot of teething problems and technical difficulties over the years, Hotvac is still the only thing out there that will permanently cure a saturated hull in a reasonable amount of time. Before we had it I'd seen boats dry for six months and barely go down on the meter. We tried all the old techniques like IR heating and the like, none compare. I've actually dried saturated foam cored hulls below the waterline with the hotvac, it's amazing. It's also the only way I've ever seen the moisture meter actually hit 5%. The science is simple and effective, makes perfect sense when you look into it...

Hotvac Boat Hull Drying, Osmosis Treatment, Osmocure

[sepeteus]

Here are the photos! Any further ideas?

[sepeteus]

One more thing. The guy who is doing the epoxy work for me mentioned (carefully) that this may have something to do with electrics and earthing of the hull. Is there any remote chance that the corrosion is causing these blisters? The old skinfittings were rooted and the new ones I bought, have a little earth clamp on them so they can be wired to main earth and avoid corrosion. It is just too much of a coincidence to have blisters only around the groups of holes. BTW to get an idea of the size, the bigger hole is inch and a half!

[buchananD]

Originally Posted by osirissail

Mr Bengt Bloomberg may have written the "bible" on blisters in Northern Europe/Sweden, but his ideas are contrary to decades of research and documentation on the subject over on this side of the Atlantic. Some of his statements are downright outrageous. We have different "bibles" that govern what we do over here to repair osmotic blisters.
- - What works for boats made in Sweden or Northern Europe is probably quite different from boats made in the USA/North America. Different manufacturers of resins and formulations and boat hull lay-up create different problems, causes and cures. - - Different strokes for different boats.

can you give examples of the contradictions and the outrageous?

[Don1500]

Originally Posted by sepeteus

Haven't done that. I will speak to the shipwright to find surveyor who do that. Thanks!

It would be cheaper to buy a moisture meter and learn how to use it properly.

[buchananD]

Originally Posted by sepeteus

Here are the photos! Any further ideas?

Basically the photos I think confirm the presence of osmosis in these local areas - some evidence of loose fibres (poor wetting out during production) and the fact the blisters were filled with a fluid tend to add further weight to this, the pH indeed the smell of the liquid and them being under pressure would also have added weight to this conclusion.

Why so local? Well I suspect the main reason is that the through hull skin fittings are too close to each other giving rise to local stresses and depending on purpose possibly local temp changes. They also, based solely on the pictures, look to lie shy of the gel coat and to be lacking in sealant. As such water penetration of the laminate is likely to have been hastened.

My original suggestion that you simply antifoul over these for now and monitor these areas and the hull more generally over the next couple of seasons would stand were it not for the fact these skin fittings seem so close together. My concern is therefore that you have seriously weakened spots on the hull that compromise the safety of the vessel. A hardness test of the laminate in these areas would help confirm any weakness. If such a test does confirm my suspicions then I would have the area properly repaired and strengthened, the skin fittings spaced out more with each properly sealed. It is really important to have the area thoroughly dried and all contaminants removed as a precursor to any repair - hotvac it as part of this process. Good luck

[buchananD]

Originally Posted by Don1500

It would be cheaper to buy a moisture meter and learn how to use it properly.

It's not in the UK but it is cheaper to cheaper borrow one from the yard. Meters in the UK are several hundred pounds rising to a thousand depending on which one you are looking at.

[Don1500]

First, correct use of the meter, read this and find the limitations of a moisture meter:
Moisture Meters on Boat Hulls - Do They Produce Reliable Results?

This is a high end moisture meter with price:
Delmhorst BD-2100 Digital Moisture Meter Inspection Kit - Mfg# BD-2100/EIFS/PKG

Cost of a survey (complete, in and out of the water) ~$500 plus. Do that twice and you've paid for the meter and any training you may need. Unless you can get the surveyor to come out for just a moisture test, then you have to negotiate the price. I am sure you would pay >$100 for just that check. And all it gets you is a moisture number, no guarantee that he is right. By learning all about the moisture meter and what it can and cannot show you will understand better what that number means.
Borrowing one from the yard is better, but yards are in business to make money. They paid for that meter, I would expect that they want a return on their investment. They may rent it to you, or they may require you to have a yard mechanic do the survey for you, charging you for it. And I would not hold that against them.

[s/v Jedi]

About the photo's: I think the thru-hull fittings are the problem. I see blue paint where the flange of the fittings go... which is anti-fouling??!

If this was my boat, this is what I would do:

- sand all that paint away

- mount new thru-hull fittings with sea-cocks or those flanged adapters on the inside. I think this boat had a nut on the inside with regular ball valves? That would NOT do for me !

- use 3M 5200 as sealant for the thru-hulls

- where gel coat was removed: fair with some epoxy

- paint & sail

ciao!
Nick.

[s/v Jedi]

Originally Posted by buchananD

It's not in the UK but it is cheaper to cheaper borrow one from the yard. Meters in the UK are several hundred pounds rising to a thousand depending on which one you are looking at.

If you have patience you can easily test without spending money. All you need is some clear plastic (cut from ziplock bags) and duct tape. Cut a rectangle and tape all around it onto the hull. Wait 24-48 hours and check for condensation behind the plastic.

ciao!
Nick.

[gonesail]

Originally Posted by s/v Jedi

In my case I have a layer of resin with chopped strands (chopper gun) that is the source. The laminate itself is underneath and untouched.

just curious Nick: what did you do or advise to others with this problem? thanks.

[s/v Jedi]

Originally Posted by gonesail

just curious Nick: what did you do or advise to others with this problem? thanks.

I'm almost finished with it. I started by grinding away -all- affected material. Next I sanded the anti-fouling and primer etc. away around the grind-spots for 1/2" or so. Next I pressure-washed it all.

Waiting for it to dry is next. The patch test as described above showed that my hull was only wet at the blisters themselves... and as I ground those away, I had no wet material left. Drying after washing (I mean drying just for the getting wet from washing) is very short: in good weather conditions 24h is enough.

Instructions for filling up are everywhere; I used epoxy, first wet the spots out, then filled with thickened epoxy. You need to repeat that a couple of times with sanding in between to get a smooth result.

ciao!
Nick.