Hull Blisters, Treatment of [Master Thread]

[Amontyg]

Just had misty pulled out for bottom paint this morning. This is the first time I've had her out of the water, and there are a bunch of little blisters pretty much all over the hull.

This is a new topic for me, and I'm just gathering some information on if/how to address this. It appears the best way is to grind out each one, dry the hull, fill, and paint. That seems like a pretty large undertaking that will take quite a bit of planning and time commitment. I'd probably be doing this work myself, since paying someone to do this would probably cost more than I paid for her. My plan for now is complete painting, relaunch, and start planning how to deal with this.

A couple questions:

How serious of a problem is this? Should I be worried about structural integrity at this point?

If this isn't a structural issue yet, how long until it becomes one? I don't think with the winter coming I have enough time left this year to tackle a project like this, so it would be at least a year before I'd have time and ability to do anything about it.

Any alternative ways of handling this I haven't seen yet?

 

[Slick470]

I did lots and lots of research before tackling ours and I came away with two major points (1) I found that there is no real consensus on what the right way to fix the problem is and (2) there was no evidence that osmosis has ever caused a structural failure on a solid layup fiberglass boat. However, it is ugly, slow, and can obviously affect resale.

For our boat, we ended up having the bottom peeled, then let it dry for a summer, while taking care of spots that needed more attention, and then fairing everything and putting glass back (and more fairing) to replace the material we took off. Lots of work, but I think it was the right call for our boat. There are lots of advocates for grinding a filling individual blisters and that was originally what I thought I was going to do.

 

[Frank Langer]

Blisters are not uncommon in older boat hulls. Although its hard to tell in the pics, yours look quite small, finger nail size not quarters or larger. It's also possible that they are in the layer between gelcoat and fibreglass, and haven't really affected the fibreglass.
If it were me, I would start by sanding or grinding to remove the bottom paint. Then I would sand or grind the next layer, likely gelcoat (unless a previous owner applied an epoxy sealer like Interprotect.) Grinding out each individual blister doesn't look feasible from your pics, so I would sand/grind until you have opened or removed the blisters, taking off as little as possible to get to that point, being careful to not gouge the hull.
At that point you'll be able to determine how many blisters are evident, how deep they are, and what repair makes sense.
My current guess is you'll need to grind off the bottom paint and gelcoat, let the hull dry (using heaters if necessary), grind any deeper blisters, fill deeper blister holes with epoxy, then coat the entire hull with about 5 coats of Interprotect 2000 which seals the hull, then apply bottom paint, and then have a beer or better to celebrate!
In not a professional, but that's my best advice. Good luck, and let us know how it goes.
Frank

 

[PANorth]

I am still in the process of a similar blister repair job. I chose to grind each blister. It took a very long time. If you go that route be sure to set yourself up with an effective dust control system as well as a full mask respirator and full coverage suit with a hood. The blisters were not consistent. Some were much deeper than others, though not any bigger around. Some had expanded in deeper layers of layup well beyond the surface blister. Our boat has been out of the water under cover for about a year. Even after hot summer months (NW Washington) we found a few blisters that were deeper and still contained liguid, so don't assume the hull is dry after a period of time. If I ever need to do this again (not on this boat for sure), I might choose soda or sand blasting to remove the top paint and or gel coast. My only reason for that is to save time. I applied glass to the deeper spots then filled the rest and faired them all. Sanding after that round also took a long time. A second round of fairing is going on now. I did some exploratory sanding today and am pretty sure more fairing will be needed. We are nearly a year into this project, though there were several events, such as high school sailing regattas every weekend last spring, and family trips that slowed things down. I hope to finish this task and several others then launch around the new year (I hope).

 

[Frank Langer]

Even after doing all this work, you can expect to find some new blisters at next haul out. That's because apparently there are areas where blisters have almost popped thru, but aren't visible on the initial repair, but continue to develop afterwards and show up later. Once you fix them, there should be no more for a while after that.
Frank

 

[Prairie Schooner]

. . . My plan for now is complete painting, relaunch, and start planning how to deal with this.

A couple questions:

How serious of a problem is this? Should I be worried about structural integrity at this point?

If this isn't a structural issue yet, how long until it becomes one? I don't think with the winter coming I have enough time left this year to tackle a project like this, so it would be at least a year before I'd have time and ability to do anything about it.

Any alternative ways of handling this I haven't seen yet?

Those are questions I have too. I'm following the answers with interest.
Perhaps this has already occurred to you, but could you do a couple test patches with different methods? That would give you a one year trial on how it works and more hands-on data as you plan the full job.
It's interesting that the keel has blisters too. Is that jacketed in fiberglass?

 

[Pete the Cat]

I have done all manner of blister treatment on 3 boats I have owned over the last 40 years. I had one bottom professionally peeled and reglassed, another where I did a grind and fill, and my present Ericson where I have a few that I am choosing to ignore. As some have noted, there is no record of a structural failure from blisters. Most blisters are between the gelcoat and fiberglass substrate, though some are the result of layup voids. Even the layup voids I found were really just that--the hull of my Tartan that had a severe blister situation and a balsa cored hull showed no penetration into the core. So my view of this is that it is largely an. esthetic thing. Surveyors and buyers (and some boatyards who are wanting business) may want to make a deal of it, but IMHO it is largely not a problem. My thought is that if it bothers you, do something. As others have mentioned, unless you strip all the gelcoat off and examine all the substrate for voids, you probably will have at least a few more when you haul next time. The Tartan I completely stripped and reglassed 25 years ago has never shown another blister, but I have beat down the other boats to almost the same level with simply working with what shows and bothers me. I disagree that these small blisters do much at all to slow a boat like we sail. It is just esthetics. But you need to do what you feel right about in your situation.

 

[jtsai]

I have done all manner of blister treatment on 3 boats I have owned over the last 40 years. I had one bottom professionally peeled and reglassed, another where I did a grind and fill, and my present Ericson where I have a few that I am choosing to ignore. As some have noted, there is no record of a structural failure from blisters. Most blisters are between the gelcoat and fiberglass substrate, though some are the result of layup voids. Even the layup voids I found were really just that--the hull of my Tartan that had a severe blister situation and a balsa cored hull showed no penetration into the core.

Pete, I did not realize the Tartan 37 has balsa cored hull. I assume it is above the waterline only? How would one approach the repair if the blisters did penetrate into the balsa core?

I just completed a 10 day adventure in New England and stayed in Stockton Spring, ME as base camp. I saw road sign to Castine but couldn't recall where I have seen that name before until read your post. Beautiful area, especially those seaside towns away from tourists.

 

[Pete the Cat]

Pete, I did not realize the Tartan 37 has balsa cored hull. I assume it is above the waterline only? How would one approach the repair if the blisters did penetrate into the balsa core?

I just completed a 10 day adventure in New England and stayed in Stockton Spring, ME as base camp. I saw road sign to Castine but couldn't recall where I have seen that name before until read your post. Beautiful area, especially those seaside towns away from tourists.

Yes, my Tartan 37 is balsa cored in some of the area below the waterline. I bought the boat in 1992 with a blister condition for a reduced price and had ithe gelcoat professionally stripped below the waterline. I was betting that Tartan probably used balsa properly and that that core would not be damaged and I was not disappointed. In fact, the stripping of all the gelcoat was an incredible overreaction on my part. The thousands of tiny blisters actually appeared to have been caused by a failed application of a barrier coat by a local boatyard--they did not let the gelcoat dry before they slapped on the Interprotect. Caused quite a mess. I stripped away a couple layers of glass that actually had some air bubbles in it, but there was no liquid in them and then put layers of epoxy cloth and had the hull professionally faired. There were a couple voids in the original layup--which I am guessing is common in many boats of the time, but no water had penetrated the core or the voids. I have seen a lot of foam cored rudders with problems and much deck rot from plywood, but in all my boatyard years not seen any problems with properly installed balsa cored hulls. End grain balsa, properly wetted with epoxy when installed, is not prone to wick or spread moisture like foam or plywood. Tartan and others generally used solid glass around the keel, deck and rigging attachment points. I repaired the balsa deck of a Nordic Folkboat I rebuilt a couple years ago by simply dropping in some epoxy coated plywood where the rotted stuff was removed and glassing it all over--folks who try to repair balsa with balsa seem to be chasing some sort of perfection that does not seem justified to me. An extra 10 oz of weight is not going to hurt the boat''s speed or contribute to strength, and the deck or hull will look the same when you fix it. I shake my head at Youtube videos of folks trying to fix a balsa deck with little squares of the material. But each to his own.

You should have come down the road 20 miles from Stockton Springs to Castine. Certainly one of the best harbors of the entire Maine Coast and a very active sailing center. I have my Tartan 37 for cruising the islands off Maine and Nova Scotia and my Ericson here in SF Bay. I consider myself exceptionally lucky to have good boats in two of the best sailing areas in the US. Next time look me up. I enjoy taking visitors out for a sail.

 

[Amontyg]

Thanks for all the replies and advise. I think unless these start growing in size on future haul-outs I’m inclined to just leave them as is.

Swung back by the marina today to check out the boat after being power washed and have a couple more problem areas I’m not sure I need to address in some way. One seems to be a crack in the top of the rudder 3-4 inches long. Not sure how this would have happened, but it does look like it goes through the gel coat to the fiberglass.
The other is a crack running vertically in the gel coat in the bow. I think this may be from a rather large log I ran into last year during a pretty turbulent sail. Other than cosmetics, are these anything to worry about?

pics attached

 

[Pete the Cat]

Thanks for all the replies and advise. I think unless these start growing in size on future haul-outs I’m inclined to just leave them as is.

Swung back by the marina today to check out the boat after being power washed and have a couple more problem areas I’m not sure I need to address in some way. One seems to be a crack in the top of the rudder 3-4 inches long. Not sure how this would have happened, but it does look like it goes through the gel coat to the fiberglass.
The other is a crack running vertically in the gel coat in the bow. I think this may be from a rather large log I ran into last year during a pretty turbulent sail. Other than cosmetics, are these anything to worry about?

pics attached

Thanks for all the replies and advise. I think unless these start growing in size on future haul-outs I’m inclined to just leave them as is.

Swung back by the marina today to check out the boat after being power washed and have a couple more problem areas I’m not sure I need to address in some way. One seems to be a crack in the top of the rudder 3-4 inches long. Not sure how this would have happened, but it does look like it goes through the gel coat to the fiberglass.
The other is a crack running vertically in the gel coat in the bow. I think this may be from a rather large log I ran into last year during a pretty turbulent sail. Other than cosmetics, are these anything to worry about?

pics attached

Sort of difficult to see the depth of the cracks in the pictures. The one in the bow is probably not much of an issue because of all the glass at that point, but the one in the rudder would concern me a bit. You do not want to get water ingressing into the foam core of the rudder as there is sometimes mild steel construction in the structures--and even it is stainless, it will not be good, as the foam they use degenerates when waterlogged. I would grind the cracks back to see how deep they are. I would probably drill some holes in the rudder (you can plug them with thickened epoxy if they are dry) to insure that your rudder has not taken on internal water.

 

[Mr. Scarlett]

Even after doing all this work, you can expect to find some new blisters at next haul out. That's because apparently there are areas where blisters have almost popped thru, but aren't visible on the initial repair, but continue to develop afterwards and show up later. Once you fix them, there should be no more for a while after that.
Frank

You're definitely correct. I just couldn't bring myself to "Like" the post.

 

[Slick470]

Our boat was sailed for years with blisters by the previous owner and then us before we were ready to deal with them, so the wait and see approach works too.

 

[G Kiba]

Barrier coat the bottom. Two coats. The Interlux brand comes in white and gray colors so you can see where you miss. Not hard to do and prevented a lot (not all) blisters the following three haul outs.

 

[Pete the Cat]

Barrier coat the bottom. Two coats. The Interlux brand comes in white and gray colors so you can see where you miss. Not hard to do and prevented a lot (not all) blisters the following three haul outs.

Just be sure your hull is dry before going the barrier coat route. As I noted above, I spent $14K peeling and reglassing the bottom of my Tartan 37 because of a crop of blisters caused by a barrier coat being applied over a wet gelcoat.

 

[Prairie Schooner]

Just be sure your hull is dry before going the barrier coat route. As I noted above, I spent $14K peeling and reglassing the bottom of my Tartan 37 because of a crop of blisters caused by a barrier coat being applied over a wet gelcoat.

Ray, How long would you let gelcoat or epoxy repairs settle before putting on barrier coat?

 

[Slick470]

a barrier coat will trap moisture in the laminate, so ideally you'd want the hull to be as dry as possible before applying it. That assumes your goal is to protect the work you've done and prevent new blisters from forming. If you are just looking to slow the process down until you have time to "right" it might be able to be used that way too. YMMV. Our bottom was covered in little dime sized or smaller "pox" so I landed with the peel approach with a barrier coat to seal things up afterward. If I had done the grind and fill individual blisters approach, I'd probably do as many as I could year one, then in subsequent haul outs do the ones that pop up and then after some number of haul outs/years and the number of new blisters is a few to none, then take all the bottom paint off, let it dry for a month or so then barrier coat.

We did a barrier coat after a peel and then let our hull dry for a summer. I went out to the boat twice a week and ground out additional spots that had dried over the previous few days and then rinsed the entire hull with fresh water. Most of the deeper spots were around a foot or so below the waterline. The guy who did our peel also did the glasswork and he visited the boat every two weeks or so and measured the moisture level in the hull and made notes on the hull with a sharpie. If I recall, his goal was to get the entire hull under 10%? It's been too long. Once the hull hit that goal, he started filling in my additional depressions and then a general fairing with me sanding in between. He then came out and did the requisite number of layers of glass to build back the lost thickness and a couple passes of fairing, more sanding from me. When he was done, he left me a bucket of fairing compound and a bottle of activator and I did several additional rounds of fairing and still more sanding.

All the fairing and re-glassing was done with vinylester as it is more water resistant than polyester. Finally, several coats of epoxy barrier coat in alternating colors, more sanding and then finally a few coats of hard bottom paint. That was 2014 and so far so good.

I saved a bunch of money by doing a lot of the sanding and fairing myself. As I get older and have less free time, I'd probably just pay someone to do it next time, if there is a next time. Although if there is a next boat might just be an epoxy or vinylester boat, we'll see.

 

[Pete the Cat]

Ray, How long would you let gelcoat or epoxy repairs settle before putting on barrier coat?

My boat was out of the water for 5 months. But much of that time was the delays in getting the thing peeled, glassed and faired; drying was a side benefit. I am skeptical of "moisture meters" that many boatyards use, but maybe they have improved; After removing layers of the original glass just under the gelcoat and putting three new cloth layers, my hull still showed 15% moisture according the meters in the boatyard (2 of them). Obviously, they should have read near 0 (I think). So I can't be much help. I talked to the PO of my boat and he said the yard pulled the boat sanded the hull a bit and put on the barrier coat all within a very short period and he thought that was the problem. Sorry I cannot be more definitive. I guess that getting all the old paint off would be my first objective. The high end Swans gave up putting gelcoat below the waterline on their boats because they believed it caused. blisters. I only put barrier directly on the faired glass--no gelcoat when I reglassed the hull. The bottom looks good after 30 years of hard use--some of it in the tropics.

 

[patrscoe]

I had a S2 11.0a that had blisters, very similar to what you have. Pox as they called it.

I hired a contractor to soda blast the hull. I spent excessive amount of hours final sanding the hull. Drilled out the blisters with a Round head drill bit (I had several sizes based on each blister size) - where goggles as sometimes the substance expodes outward and I didn't want it in my eyes or on my face.
Filled in and faired using a 3M epoxy watertight and then final sanded the areas.
Applied several coats of epoxy barrier coat / bottom paint as you need to apply the bottom paint after the last coat of barrier coat per directions for a chemical adhesion.

What I remember more than anything (2008); I had a quote for $4,200 from the boat yard. I spent $1,100 - again, back in 2008. After countless hours of really hard work, I looked at my wife as I was putting the last coat of bottom paint on at 9pm (becuase the final weekend took All day Saturday and All day Sunday and into the night), said to my wife, I would have paid $5k for the boatyard to do this work.
Repairing handful of blisters - no problem. but I think I roughly counted 300 to 320 blisters of all sizes.

Also, after soda blasting, sanding and drilling out the blisters, I also let it sit for about 3 months.

Like having a child, I look back at it now, and say, that wasn't too bad.

 

[patrscoe]

Blisters form any where there is epoxy was laid up so the keel is not excluded from this as they encapslate the keel with glass.
After I did this on my S2 11.0a, I did not see any blisters come back and sold her in 2012 blister free.