Blisters, yet again...

I have spent a few days reading everything I can find on this subject in TF and also on the internet. The amount of information and conflicting opinions out there is a bit overwhelming. There are some really good TF threads, but some are a bit old and products and solution strategies may have changed(?)…so I’m sorry, I feel compelled to start another thread on this.

My 33’ boat is 10 years old and for the last three winters I’ve had to deal with (an ever-increasing number of) small blisters below the waterline. It used to be 25-50 blisters. As of the most recent haul-out, however, I think there may be a couple hundred or more. These blisters are, indeed, in the gel coat, not the paint. When popped, the fluid that comes out is clear, thin and watery. Not dark. The strategy my yard has used so far has been to grind each blister, fill and paint. The situation shows no signs of slowing. I am getting tired of this and am also concerned about the long-run implications of not fully addressing the problem, as I intend to keep this boat for quite some time.

A few weeks ago, I asked the manufacturer of my boat if they had any experience with this and if they could provide any recommendations. To my surprise, they responded rather quickly with a recommendation and, upon my asking, offered that I could purchase the work through them, even though the actual work would be done by a sub-contractor. There are aspects of this arrangement I find appealing. They would offer a two year warranty (but I have no specifics yet).

The manufacturer is proposing:
- Anti-fouling removal
- Complete gelcoat peel (entire bottom, even though blisters are currently only aft of midship.)
- Vinylester putty
- Spray on new gelcoat
- Anti-fouling primer (epoxy barrier coat)
- Anti-fouling paint

The manufacturer has expressed flexibility in letting me specify products for the “finish” work. This is both good and bad. While I think I may have some preferences, this is an area I know precious little about and find very confusing. I don’t want to specify something that might be, in the long run, a poor solution. As such, I’m grateful to have access to the thousands of years of cumulative knowledge and experience of Trawler Forum members ;-)

While I will be grateful to have any and all TF input on this, I will start with four specific questions:

1) My hull is polyester resin, as it’s one of their early models. Newer models use vinylester resin. From the research I’ve done, it seems that Vinylester putty should, indeed, be compatible with polyester resin. Does anyone disagree with this?

2) After removing the gelcoat, should I consider not replacing it and using some epoxy system instead? For example Interlux Interprotect 2000, International Gel-shield Plus, Jotun Osmoshell? Probably not WEST system, based on what I’ve read. BUT – can any type of epoxy coatings be used on polyester/vinylester ?? I have read about different flexibility characteristics of these two materials…that could lead to problems.

3) The boat has now been out of the water and inside a building for a year now (due to Corona). So, in one sense, it’s quite dry, but as I understand from reading a lot of drying (and possibly rinsing) has to occur after the gelcoat has been peeled. As such, I’m wondering if I should break the project up into a gelcoat peel in November and wait until March for the rest of the work. Would this be long enough for “natural” dry-out? Or, should I still be asking about HotVac or some other drying accelerator. Perhaps this question cannot be accurately answered until the gelcoat comes off??

4) Should through-hulls be removed for such a project? (My guess is that the answer to this will be “ideally, yes”)

Thanking you in advance,
ScottC

First, do you have a thorough understanding of hydrolysis versus osmotic blistering?

I ground off the gel coat, all matting and some areas of saturated roving.

Rebuilt the delaminared areas (one was 5 ft by 6 ft by 1/2 inch deep), rolled on a generic epoxy coat, laminated a 6oz cloth layer, rolled on 2 more coats of generic epoxy.then Interprotect 2000 per factory recommendations..

Not one blister or delam after 8 years continuous immersion, part of the year in warm waters.

psneeld said:

First, do you have a thorough understanding of hydrolysis versus osmotic blistering?

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Well, I did read about it - and in particular in some of your posts. If I understand correctly, the appearance of blisters only confirms that I have hydrolysis. And the extent of the damage due to this cannot really be determined until the gelcoat is removed. Is it only under the gelcoat? Or have one or more layers of mat been damaged?? I am guessing (perhaps just wishful thinking) that because the blisters are so small, maybe I will not find much in the way of delamination yet...

I'd peel it and build everything back up with epoxy. Their proposal to use vinylester putty and gelcoat is just to use slightly less expensive materials. You'll likely not know how deep you'll need to dig into the laminate until after it's peeled.

The manufacturer who created the blisters is proposing to repair it and you specify materials??? How long is their warranty for the repair? I think you would benefit from soliciting some quotes from some other yards that specialize in fiberglass work.

SoWhat said:

The manufacturer who created the blisters is proposing to repair it and you specify materials??? How long is there warranty for the repair? I think you would benefit from soliciting some quotes from some other yards that specialize in fiberglass work.

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2 yrs. Warranty
I agree totally with getting some other qoutes.
One thing I’m struggling with is that the boat is in France and I am in Sweden. This is because of Corona. Since this could be a lengthy project, I thought it might be nice to do it while I can’t use the boat. But I don’t like the thought of doing this when I can’t make frequent mid-project check ups.

My take? Why the blisters appeared after 6-7 years and have been getting progressively worse needs some answers from Greenline. FRP vessels built in the past decade should be using products and techniques as perfected in the previous 50 years of using FRP to avoid blisters.

PSN touched on the primary go forward concern, do it right so it doesn't have to be done again for a very long time. A two year warranty from Greenline seems a poor reason to do business with them.

I would do a peel and build back with epoxy not a lesser resin. The cost difference will be insignificant in the overall project cost. I like the interlux Interprotect system. I have used it on multiple boats and never had a reoccurrence of blisters. A 2 year warranty seems pretty lame when we are talking blisters. Why do they want to put gel coat back on instead of an epoxy paint? Epoxy is the way to go for everything IMO. If they built boats below the waterline with epoxy I don’t think blistering would ever be an issue. Our current boat was peeled and then coated with Interprotect and that was many years before we bought it and still has no blisters.

ScottC... I urge you to go back to your readings.....and follow your instincts.

I am sure if you did 1/4 the research I did, you are seeing the assumptions and personal opinions instead of industry specific experiences and suggestions to the problems and fixes.

As you probably have read, most yards, surveyors, magazine writers, etc...etc.... only speak of the basics of the whole process.

ScottC said:

Well, I did read about it - and in particular in some of your posts. If I understand correctly, the appearance of blisters only confirms that I have hydrolysis. And the extent of the damage due to this cannot really be determined until the gelcoat is removed. Is it only under the gelcoat? Or have one or more layers of mat been damaged?? I am guessing (perhaps just wishful thinking) that because the blisters are so small, maybe I will not find much in the way of delamination yet...

Click to expand...

If the fluid coming from the blisters is clear. It is highly unlikely that hydrolysis is involved. I've seen hundred of cases of hydrolysis and it has always looked like malt vinegar with a very acidic taste.

PS. My son is working in Malmo

Old threads are just as applicabe as new one’s IMO.

I have blisters that I tend to every 2 to 5-6 years. They are all below the WL and 3/4 to 1” in dia. I grind down about 3/32nd to 1/8” to solid FG. Mix up some epoxy somewhat hot and put the epoxy in/on the divits/holes. Sand where needed and apply regular bottom paint after.

Well under a days work and slowly but steadily declining. I consider it a minor bother.

Here's just one of my sources for info...it's a PDF white paper so this is not a link...Googling may work.

BLISTERS & LAMINATE HYDROLYSIS
by Craig Bumgarner
Updated April 9th, 2003

20 years ago I had the chance to deal the blister on my 1990 Carver 38 that had some 300 to 400 Blister below the water line. I have purchased the boat knowing that I have to deal with them over the winter season before Spring launch.
1) The boat was sand blasted once the boat was on the dry for the winter and left to dry over the winter (Upper Chesapeake Bay).
2) over Spring time, all the blisters were grinded, cleaned with alcohol, filled the blisters with blisters fix material, sanded the bottom accordingly then applied 3 coats of Interlux 2000/2001 barrier coating and 2 coats of bottom paint.
I did not have any blisters there after until the was sold 16 years later.
Blister are common to boats and are easy to fix your self.
good luck,

Clearly Greenline knows they had a problem and they're just happy the boat made it through their five year warranty before blistering. Why do I say this? Most builders would be indicating to you that it probably wasn't serious and they'd recommend you have a yard look at it. When the builder immediately suggests a complete gelcoat peel and a different resin than what they originally used, it indicates to me they've had widespread issues and they know the cause. I would try to get them to tell me what they know and cause and what they've changed since.

Clearly they know you're fighting a losing battle approaching it the way you have and with the recurring problems.

I would take their advice and talk to the people they use as well as others and then proceed with someone you have confidence in.

A boat the vintage of yours should not be having this problem to the extent you have and, in my opinion, this is a significant manufacturing defect. However, it's also a correctible one as I believe has likely been done many times.

Sounds like Greenline have been there before. It`s possible/likely they have a good handle on this so don`t rule their repair system out.
I explored a fix while considering several Integrity boats which as far as I can tell, were built with neither a barrier coat or a good gelcoat .My previous IG boat had relatively deep sporadic large blisters repaired. I`m no expert but have experienced "osmosis blisters' and researched repairs on intended purchases. It may help,or not.
I was told a vinylester outer coat doesn`t go off well without adding a layer of glass. If the strip back is by "peel planing" you might want the extra glass layer. "Vinylester putty" could be a way adding glass. The other way is rolling 2-3 layers of epoxy over the repaired hull. If defects remain you are locking them in and it will fail again.
Are your blisters invading the fibreglass? You`ve been grinding so I expect "yes". Your description of the blister fluid didn`t sound like the nasty vinegary stuff I saw from "osmosis" blisters, not sure what that indicates, except it made me ask if the fibreglass was being invaded.

If you use a non-epoxy paint over an epoxy barrier coat, the first coat of that bottom paint must be applied before the epoxy transitions to the final stages of cure. Thumb print tack is the typical time to apply bottom paint. This ensures a chemical bond between the two. So timing of each step is important. An example is use of an ablative bottom paint over Interlux 2000. I used red bottom paint for the first coat, and followed with black over that red guide layer. When red begins to show, it's time for a new coat of black. We did an epoxy barrier coat (Interlux 2000) plus bottom paint 15 years ago and haven't seen a blister since.

By the way, epoxy is not UV tolerant, so any areas above the water line must be protected.

I wonder if this might be covered by your insurance as a latent defect. When this happens in older boats it's because they were built before this issue was well understood. But for it to exist in a 10 year old boat is a pretty big "oops" by the manufacturer.

Question on repair: I don't see recommendations to epoxy laminate a thin skin of fiberglass mat over the peeled hull. I've seen this being done and would think it would be far superior to paint-on Interlux 2000 alone. Would it be preferable to add a layer of epoxy mat?

As far as re-gelcoating the bottom, that sounds nuts to me. Gelcoat tends to be a bit porous and is best used inside a mold, not as a painted product. I don't know Greenline so can only speak to boat builders in general, but many are not particularly savvy on boats. They are good custom manufacturers who understand fiberglass, but not necessarily skilled in the nuances of boats and how they are used.

Peter

Post #2 ...I posted a 6oz cloth layer went on to replace the matt/gel over any putty for holding plus as an extra thick barrier coat before the Interprotect that helped smooth the surface.

A giant PIA trying to do it myself, but done.

psneeld said:

Here's just one of my sources for info...it's a PDF white paper so this is not a link...Googling may work.

BLISTERS & LAMINATE HYDROLYSIS
by Craig Bumgarner
Updated April 9th, 2003

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Found it. Thanks! Printed it out so I can read it with a hi-lighter.

Do not reapply gelcoat to the repair. I find it with blisters on every hull I have seen that has gelcoat sprayed around bow thruster holes, underwater exhaust, trim tab pockets etc. that are installed post lay-up or just touched up.

Best way to figure out what to do is to have a small section investigated to examine the nature and extent of the damage then proceed with an appropriate repair process.

psneeld said:

Post #2 ...I posted a 6oz cloth layer went on to replace the matt/gel over any putty for holding plus as an extra thick barrier coat before the Interprotect that helped smooth the surface.

A giant PIA trying to do it myself, but done.

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Gotcha. I missed that.

The workmen I watched do it on a sailboat were talented and fast. If I were to do it, would end up a total mess of crinkle zones. Maybe in today's world of YouTube video instruction I could do a decent job at fiberglas, but my prior efforts did not end well. Reminiscent of a 3 year old making Play-Doh figurine.

Peter

ScottC said:

Found it. Thanks! Printed it out so I can read it with a hi-lighter.

Click to expand...

One source, not the final.

I probable learned more from the underground fiberglass pipe and tank industry more so than the boating industry.

Small area test saying is almost mandatory to identify hydrolysis, there are other symptoms that may....but ultimately small area testing doesn't really show the full extent. Once some is found/suspected...more extensive destructive testing is required. A decent step is pull widespread thru hulls and try and check for hydrolysis in the laminates exposed there.

twistedtree said:

I wonder if this might be covered by your insurance as a latent defect. When this happens in older boats it's because they were built before this issue was well understood. But for it to exist in a 10 year old boat is a pretty big "oops" by the manufacturer.

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Good point. I asked my insurance company (Pantaenius) a few years ago when this started and they responded that "Osmosis" was not covered. I left it at that at the time, because I thought blisters = Osmosis. End of story.

I have just now sent them a follow-up mail asking them if it would be covered if this could be proven to be a manufacturing defect.

sunchaser said:

My take? Why the blisters appeared after 6-7 years and have been getting progressively worse needs some answers from Greenline. FRP vessels built in the past decade should be using products and techniques as perfected in the previous 50 years of using FRP to avoid blisters.
.

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I very much suspect this is why, after the first few years of production, Greenlines going forward were built using vinylester instead of polyester. Unfortunately, my hull is from early in their first year of production.

boatpoker said:

If the fluid coming from the blisters is clear. It is highly unlikely that hydrolysis is involved. I've seen hundred of cases of hydrolysis and it has always looked like malt vinegar with a very acidic taste.
PS. My son is working in Malmo

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Thank you for this, boatpoker! This experience is very useful in helping me better understand what might be going on.

Interesting that your son is working here! There is a rapidly growing international presence in Malmö.

BandB said:

Clearly Greenline knows they had a problem and they're just happy the boat made it through their five year warranty before blistering. Why do I say this? Most builders would be indicating to you that it probably wasn't serious and they'd recommend you have a yard look at it. When the builder immediately suggests a complete gelcoat peel and a different resin than what they originally used, it indicates to me they've had widespread issues and they know the cause. I would try to get them to tell me what they know and cause and what they've changed since.

Clearly they know you're fighting a losing battle approaching it the way you have and with the recurring problems.

I would take their advice and talk to the people they use as well as others and then proceed with someone you have confidence in.

A boat the vintage of yours should not be having this problem to the extent you have and, in my opinion, this is a significant manufacturing defect. However, it's also a correctible one as I believe has likely been done many times.

Click to expand...

My hull is from their first year of production (2010). At some point after this, they changed from polyester to vinylester....and went from a 3yr warranty to a 5 yr warranty.

I tend to agree with you that the swiftness and completeness of their response to my question suggests that they've dealt with this before.

Complicating this is the fact that Greenline today, while made in the same factory and with some of the original molds, is actually a different company. The original company that built my boat, SeaWay, went bankrupt around 2015-ish and the remaining assets were bought by another company, SVP Yachts. Most of the original employees, are no longer there, as I understand it.

The SVP folks have been surprisingly helpful with various support questions and component needs I've had since they took over in 2015 and I think they're a good company. They have learned a lot and the product line has evolved in an impressive way. If I were in the market for a new hybrid today, would I consider Greenline again? Absolutely.

As frustrating as it is, I don't see that they have any legal obligation for my current situation and I don't see much point in going to the expense of pressing it and risk damaging the otherwise good relationship I currently have with them.

One thing that appeals to me about arranging the work to be done through the manufacturer is that they fully understand the hull shape, hull contstruction and light-weight design. Any gelcoat peeling would have to be performed in a dead-accurate manner and if any delamination were to be found in some of the areas where the bottom is thinner, then it would be comforting to me to have the factory calling the shots for the sub-contractors doing the actual work. I'm learning in this thread that a 2-year warranty for blister work sounds a little scant. But, I would also be looking for that warranty to cover any possible damage to structural integrity from the work, which I think, if it existed, would be likely to present itself within two years. I would want to see the details of the warranty to be sure!

I have dealt with blisters on all two 40 foot trawlers that I have owned. I chose not to deal with blister by blister although it might have worked. I had the yard grind off my bottom paint and the gelcoat. After some drying with heat he went back with epoxy. My hulls were sufficiently thick he did not add any glass. Then barrier coat and new bottom paint. No more blisters after that.

Rufus said:

If you use a non-epoxy paint over an epoxy barrier coat, the first coat of that bottom paint must be applied before the epoxy transitions to the final stages of cure. Thumb print tack is the typical time to apply bottom paint. This ensures a chemical bond between the two. So timing of each step is important. An example is use of an ablative bottom paint over Interlux 2000. I used red bottom paint for the first coat, and followed with black over that red guide layer. When red begins to show, it's time for a new coat of black. We did an epoxy barrier coat (Interlux 2000) plus bottom paint 15 years ago and haven't seen a blister since.

By the way, epoxy is not UV tolerant, so any areas above the water line must be protected.

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I like the two-color idea, Rufus and will certainly use that strategy I end up going the epoxy route. Thanks for the clever tip!


I have ~6 inches of bottom color that is above the waterline. No blisters in this area, thus far. I wonder if this should be treated in the same manner as the bottom? (i.e. peel and epoxy, for example). If yes, do you know if anti-fouling paint could be expected to protect the epoxy from UV damage?

For the 2 color route, I'd personally use a hard paint for the first layer, then a compatible ablative over that. That way you don't have to worry about wearing through the different color layer at any point.

I'd do the full treatment to any area that has bottom paint, even if it's above the normal loaded waterline. The bottom paint should provide plenty of UV protection.