So, your boat has just been hauled. Inspecting the bottom, you are pleased to find no hard growth and the through hulls and the running gear look pretty good. But then you notice these little bumps in the paint.... Blisters. Most fiberglass boats will develop some blisters in their lifetimes. Sometimes they are just little bubbles in the paint in a few locations. Other times, blisters may appear as quarter or half-dollar size eruptions here and there. And in some extreme cases, the entire bottom may be covered with a pox of blisters that extend into the laminate. Has your boat ever had blisters? If so, how did you deal with them? Cut them open, dry them out, and fill with epoxy? Was it a DIY job or did you hire a professional? How serious do you really think blisters are? Share you views about blisters here and then take the Quick Quiz on the homepage. (Discussion topic and quiz by Warren Milberg)
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What I did
Sometimes blisters are just in the bottom paint. One must determine if that is the case. I did have an Irwin 32 that had some blistering at the hull/keel joint. At haulout I would find maybe a dozen small blisters. i opened them up and let them dry out over the winter. In the spring I used West epoxy to fill the holes and each year the problem got better. I did finally strip the bottoma nd barrier coated and then the problem stopped.
Sometimes blisters are just in the bottom paint. One must determine if that is the case. I did have an Irwin 32 that had some blistering at the hull/keel joint. At haulout I would find maybe a dozen small blisters. i opened them up and let them dry out over the winter. In the spring I used West epoxy to fill the holes and each year the problem got better. I did finally strip the bottoma nd barrier coated and then the problem stopped.
'88 HL35 Never Had a Blister 
We've owned our 1988 HL35 boat since new and I'm happy to report that we've never had a blister. Put on an epoxy barrier coat when it was new so that's probably been the reason why. It cost a few bucks back then but I think it's been worth it.
We've owned our 1988 HL35 boat since new and I'm happy to report that we've never had a blister. Put on an epoxy barrier coat when it was new so that's probably been the reason why. It cost a few bucks back then but I think it's been worth it.
An expensive but necessary fix
I own a 1984 O'Day 24. We purchased it used knowing that it had been in the water for some time. The survey noted "some blistering" which we chose to ignore. Two years later that "some blistering" had become become more noticable. I instructed the boatyard to sandblast the bottom so that we could see what was happening. I am not sure I'd do it this way again since this openned hundreds of eraser sized to quarter sized and larger blisters everywhere. Since I derive no pleasure from the odor of epoxies and holding my arms over my head for hours at a time, this was not a DIY fix for me.
I own a 1984 O'Day 24. We purchased it used knowing that it had been in the water for some time. The survey noted "some blistering" which we chose to ignore. Two years later that "some blistering" had become become more noticable. I instructed the boatyard to sandblast the bottom so that we could see what was happening. I am not sure I'd do it this way again since this openned hundreds of eraser sized to quarter sized and larger blisters everywhere. Since I derive no pleasure from the odor of epoxies and holding my arms over my head for hours at a time, this was not a DIY fix for me.
Don't ignore it
When I purchased my Oceanis 390, there was a small amount of blistering. I negotiated with the seller to drop the price by the amount it would take to fix it - eventually, he agreed. After the haulout at the end of the season, I opened up the blisters that the seller had circled years before to make sure that they weren't growing. Almost all were very small and could have survived just fine. One was the size of a pinkie finger and about 1" deep. A couple of more years and my guess is it would have been through the hull. So get them fixed - the earlier, the more likely you can correct the problem yourself.
When I purchased my Oceanis 390, there was a small amount of blistering. I negotiated with the seller to drop the price by the amount it would take to fix it - eventually, he agreed. After the haulout at the end of the season, I opened up the blisters that the seller had circled years before to make sure that they weren't growing. Almost all were very small and could have survived just fine. One was the size of a pinkie finger and about 1" deep. A couple of more years and my guess is it would have been through the hull. So get them fixed - the earlier, the more likely you can correct the problem yourself.
Over a Hundred!
We bought a '73 Cal 25, which was in very nice shape for a cheap, old boat. But the reason it was in nice shape was that the owner seldom used it and it had been sitting in the water for over 5 years. That seems to be the root cause of much blistering, and sure enough we had over a hundred blisters, perhaps 25 of them in the quarter-size range. We sanded the whole hull down to the gelcoat and then I actually drilled out (carefully!) each blister and filled it with a top-grade fairing compound. We then applied barrier coats and bottom paint. It looked great when we were done and has floated almost a year since. While we think this has cured our boat, we won't know for a few years. One thing I do know is that I don't want to ever go through the process again!
We bought a '73 Cal 25, which was in very nice shape for a cheap, old boat. But the reason it was in nice shape was that the owner seldom used it and it had been sitting in the water for over 5 years. That seems to be the root cause of much blistering, and sure enough we had over a hundred blisters, perhaps 25 of them in the quarter-size range. We sanded the whole hull down to the gelcoat and then I actually drilled out (carefully!) each blister and filled it with a top-grade fairing compound. We then applied barrier coats and bottom paint. It looked great when we were done and has floated almost a year since. While we think this has cured our boat, we won't know for a few years. One thing I do know is that I don't want to ever go through the process again!
Had lots!
The purchase of my 1984 O'day 30 was discounted by the cost of repair of numerous blisters. The boat's previous owner did NOT believe in repairing them - thinking that they were only "cosmetic." Well - even after survey - it seems he was mostly right! All but two of the ugly things were "air bubbles" in the anti-fouling. I stripped everything off the bottom, dried out the two "real" blisters, and - after repairing those - applied Vinylester under my annual spray coat of VC-17. Looks good - and has been trouble-free for the last 5 years. I'm happy! Bill on STARGAZER
The purchase of my 1984 O'day 30 was discounted by the cost of repair of numerous blisters. The boat's previous owner did NOT believe in repairing them - thinking that they were only "cosmetic." Well - even after survey - it seems he was mostly right! All but two of the ugly things were "air bubbles" in the anti-fouling. I stripped everything off the bottom, dried out the two "real" blisters, and - after repairing those - applied Vinylester under my annual spray coat of VC-17. Looks good - and has been trouble-free for the last 5 years. I'm happy! Bill on STARGAZER
Skinned
I purchased several boats over the years and found blisters are not unique to a particular brand. While some brands have fewer than others, the one that was the most extreme. I purchased a Gulfstar 40 Sailmaster, 1982 model that had so many blisters that we had the gel coat removed completely below the water line. While they were not deep, the cost to skin the hull and rebuild was the lesser of two evils. As it turned out, we let the hull dry for several months, added another layer of woven roving and put 7 coats of Interprotect 1000/2000. Then did the usual bottom paint. After 4 years, there were some dozen or so, blisters, none through the fiberglass. It appeared that they formed where the Interprotect may have had some flaws. Although we no longer own the boat, the current owner reported that on last haulout it was nearly blister free (about 3 years after the skinning).
I purchased several boats over the years and found blisters are not unique to a particular brand. While some brands have fewer than others, the one that was the most extreme. I purchased a Gulfstar 40 Sailmaster, 1982 model that had so many blisters that we had the gel coat removed completely below the water line. While they were not deep, the cost to skin the hull and rebuild was the lesser of two evils. As it turned out, we let the hull dry for several months, added another layer of woven roving and put 7 coats of Interprotect 1000/2000. Then did the usual bottom paint. After 4 years, there were some dozen or so, blisters, none through the fiberglass. It appeared that they formed where the Interprotect may have had some flaws. Although we no longer own the boat, the current owner reported that on last haulout it was nearly blister free (about 3 years after the skinning).
Only a few.
I bought a 1980 Cherubini Hunter 33' last year. The survey haul out sealed the deal when the hull only appeared to have 8 blisters after the boat yard pressure washed 2 years worth of slime off of the hull. Even the boat yard folks were impressed with how clean the hull was. Then it turned out that 5 of the 8 were only bubbles under the anti-fouling . The 3 actual blisters were only aprox 1/4 - 1/3 inch deep and the largest was slightly wider than a quarter. I repaired them DIY by grinding them out oversized with a shallow slope to the hole sides for plenty of overlap for the several layers of progressivly larger circles of woven glass and West Sytems epoxy. Took just 4 hours total to fix all 3 blisters plus epoxy cure time. I then applied a barrier coat over the blister repairs before painting the entire hull with 2 gallons of a high quality hard anti-fouling paint, which gave me 2 generous coats over most of the hull, and up to 6 coats over all leading edges by the time i used up all the paint.
I bought a 1980 Cherubini Hunter 33' last year. The survey haul out sealed the deal when the hull only appeared to have 8 blisters after the boat yard pressure washed 2 years worth of slime off of the hull. Even the boat yard folks were impressed with how clean the hull was. Then it turned out that 5 of the 8 were only bubbles under the anti-fouling
. The 3 actual blisters were only aprox 1/4 - 1/3 inch deep and the largest was slightly wider than a quarter. I repaired them DIY by grinding them out oversized with a shallow slope to the hole sides for plenty of overlap for the several layers of progressivly larger circles of woven glass and West Sytems epoxy. Took just 4 hours total to fix all 3 blisters plus epoxy cure time. I then applied a barrier coat over the blister repairs before painting the entire hull with 2 gallons of a high quality hard anti-fouling paint, which gave me 2 generous coats over most of the hull, and up to 6 coats over all leading edges by the time i used up all the paint.A fix for the blisters
I fixed my blisters with a company called thermocure. They leterally bake the hull and extract the moisture and most importantly set off the left over styrene that cuases the blisters. I had it done 3 years ago and still have a moisture rating of 0. Well worth a look.
I fixed my blisters with a company called thermocure. They leterally bake the hull and extract the moisture and most importantly set off the left over styrene that cuases the blisters. I had it done 3 years ago and still have a moisture rating of 0. Well worth a look.
More Details on Interprotect coating
Howell, can you give me some more details on your work? My second boat is a 1970 19' Flying Scott. It's gel coat is completly cracked and blistered, not just a few dozen pocks. It has dried out in my garage for 10 years and now I want to heal the hull. I flipped it over and my plan is to grind off the gell coat to the laminate. How did you apply the 7 coats of Interprotect? Filler type and amount? Application method? Time between coats? Control of coating thickness? Getting a fair and smooth hull? When to apply final antifouling coat? etc. Thanks. Harry "Refresher"
Howell, can you give me some more details on your work? My second boat is a 1970 19' Flying Scott. It's gel coat is completly cracked and blistered, not just a few dozen pocks. It has dried out in my garage for 10 years and now I want to heal the hull. I flipped it over and my plan is to grind off the gell coat to the laminate. How did you apply the 7 coats of Interprotect? Filler type and amount? Application method? Time between coats? Control of coating thickness? Getting a fair and smooth hull? When to apply final antifouling coat? etc. Thanks. Harry "Refresher"
Blisters are a problem
Blister problems are in the gelcoat and not the paint as the lead in paragraph suggests. You can have blisters in paint, but when people talk of blister problems, they mean gelcoat. As someone else wrote, it is an industry problem and not isolated to particular brands. Older boats usually suffer blisters while newer boats that have more modern resins and gelcoats used, are more blister prone. It appears that fresh water boats have a bigger blister problem than salt water boats. It has been documented that a 30 foot sailboat with blisters can add 1000 lbs of water weight. If you have a terribly old boat that is not worth much, then I might consider not fixing the blisters. The job, if done professionally, might cost more than the vessel itself. But, if you have a boat that is worth something in good condition, then I would consider parting with your cash. To fix the problem you have to open up the blisters in the hull. This can be done by either sandblasting or stripping the gelcoat off with a special tool. The bad, blistered gelcoat must be removed and then the hull must be dried out. Some people simply sand the blisters smooth and then apply epoxy water barriers over the hull. Not a good idea. Inside the blisters and the gelcoat is moisture. That is why the blisters are there. Gelcoat has been found to not be waterproof as previously believed. Sanding the blisters smooth does not rid the hull of the problem and certainly does not remove the moisture. Blister repair is a big, tough and lousy job and unless you like to do this type of work, I suggest hiring your boatyard to do this work. Ok, remove the bad gelcoat and dry the hull. If you live in a humid area, this might be tougher to do. However you do it (put it inside a controled climate, let it dry all winter long - whatever - make sure you dry it out). Then you can start applying barrier coat products. But, you are wasting your time and money if you apply barrier coats over a wet hull. You will end up doing it all over again. Use epoxy products as they are waterproof. I particularly think the Interlux Interprotect system is the best, but there are others out there. Vinylester resins are epoxy modified resins that have more waterproofness than most resins used for hull building (orthophalic or isotphalic - spelling might be off). I have seen some product manufacturers come out with vinylester resins that did not have good results with blister repairs. Some might, but I know that epoxy for sure does. Whatever system you use, follow the directions implicitly. Also keep in mind that epoxy products are dangerous to use in comparison to polyester resins. You can become sensitized to epoxy, so you must protect yourself while using it. Do not let it touch your skin. Protect your lungs, wear protective clothing, etc. If you ever get sensitized to epoxy, you will not ever be able to go into the same room with it. It can be that bad. Also, unlike polyester, which will harden if you don't get the exact resin to hardner mixture, epoxy must be exactly mixed with the proportions stated on the info of whichever epoxy you are using. Failure can result if you don't follow this. One good thing about the Interprotect system is you can apply several coats within a shorter period of time (dictated by the ambient temperature). If it is hotter out, then you can apply coats in less time between coats. If it is cooler out, you have to wait longer between coats. But many epoxies are designed for one coat per day. If you need 7 coats, that is a week of applications and you still need to sand and apply antifouling paint, not to mention the fairing required after sandblasting or stripping. So,if you can apply the product every two hours on a hot day, that is a good thing. Check the product labels. There are drying solvents that help the epoxy cure. If you apply coats sooner than recommended based on the temperature, you will not let the paint dry enough between coats which will give you other problems, such as alligatoring (wrinkling). And, if you wait too long between coats, you will surpass the window of drying so that you will have to sand your last coat for the new coat to get a good tooth. If you do it in the prescribed time window, then you will not have to sand between coats. Read the system directions and follow them well and you will do all right.
Blister problems are in the gelcoat and not the paint as the lead in paragraph suggests. You can have blisters in paint, but when people talk of blister problems, they mean gelcoat. As someone else wrote, it is an industry problem and not isolated to particular brands. Older boats usually suffer blisters while newer boats that have more modern resins and gelcoats used, are more blister prone. It appears that fresh water boats have a bigger blister problem than salt water boats. It has been documented that a 30 foot sailboat with blisters can add 1000 lbs of water weight. If you have a terribly old boat that is not worth much, then I might consider not fixing the blisters. The job, if done professionally, might cost more than the vessel itself. But, if you have a boat that is worth something in good condition, then I would consider parting with your cash. To fix the problem you have to open up the blisters in the hull. This can be done by either sandblasting or stripping the gelcoat off with a special tool. The bad, blistered gelcoat must be removed and then the hull must be dried out. Some people simply sand the blisters smooth and then apply epoxy water barriers over the hull. Not a good idea. Inside the blisters and the gelcoat is moisture. That is why the blisters are there. Gelcoat has been found to not be waterproof as previously believed. Sanding the blisters smooth does not rid the hull of the problem and certainly does not remove the moisture. Blister repair is a big, tough and lousy job and unless you like to do this type of work, I suggest hiring your boatyard to do this work. Ok, remove the bad gelcoat and dry the hull. If you live in a humid area, this might be tougher to do. However you do it (put it inside a controled climate, let it dry all winter long - whatever - make sure you dry it out). Then you can start applying barrier coat products. But, you are wasting your time and money if you apply barrier coats over a wet hull. You will end up doing it all over again. Use epoxy products as they are waterproof. I particularly think the Interlux Interprotect system is the best, but there are others out there. Vinylester resins are epoxy modified resins that have more waterproofness than most resins used for hull building (orthophalic or isotphalic - spelling might be off). I have seen some product manufacturers come out with vinylester resins that did not have good results with blister repairs. Some might, but I know that epoxy for sure does. Whatever system you use, follow the directions implicitly. Also keep in mind that epoxy products are dangerous to use in comparison to polyester resins. You can become sensitized to epoxy, so you must protect yourself while using it. Do not let it touch your skin. Protect your lungs, wear protective clothing, etc. If you ever get sensitized to epoxy, you will not ever be able to go into the same room with it. It can be that bad. Also, unlike polyester, which will harden if you don't get the exact resin to hardner mixture, epoxy must be exactly mixed with the proportions stated on the info of whichever epoxy you are using. Failure can result if you don't follow this. One good thing about the Interprotect system is you can apply several coats within a shorter period of time (dictated by the ambient temperature). If it is hotter out, then you can apply coats in less time between coats. If it is cooler out, you have to wait longer between coats. But many epoxies are designed for one coat per day. If you need 7 coats, that is a week of applications and you still need to sand and apply antifouling paint, not to mention the fairing required after sandblasting or stripping. So,if you can apply the product every two hours on a hot day, that is a good thing. Check the product labels. There are drying solvents that help the epoxy cure. If you apply coats sooner than recommended based on the temperature, you will not let the paint dry enough between coats which will give you other problems, such as alligatoring (wrinkling). And, if you wait too long between coats, you will surpass the window of drying so that you will have to sand your last coat for the new coat to get a good tooth. If you do it in the prescribed time window, then you will not have to sand between coats. Read the system directions and follow them well and you will do all right.
A few more comments
If you see a few blisters, then assume that you have a lot more that you cannot see. I have seen blisters on boats that just came out of the water and after the boat sits, the blisters sometimes (not always) go away. And you want to believe the problem doesn't exist, but it does. One person wrote about blisters in the keel to hull joint area. The blisters were most likely in the fairing compound used to smooth out that section. The keel which was either lead or metal didn't blister and the hull didn't, but the faring compound, which was more susceptible to moisture did. Perhaps a polyester and not an epoxy compound was used. Sometimes you see blisters in the waterline paint. If it was gelcoat, it might not blister, but if the wrong paint was applied (usually be the boat owner)then it could blister. Urethane paints are not guaranteed under the waterline. If your stripe sits submerged all season, and it is a Urethane paint, it will blister. Alwgrip or Awlcraft is wonderful paint, as long as it is above the waterline. Have antifouling paint creep above the waterline and then the waterline stripe or stripes should be painted above that. Epoxy paints are more waterproof, but they can't hold up to sunlight as well as urethanes and will chalk much more rapidly. Painting is another subject. Don't confuse gelcoat blisters with paint blisters. If you see your antifouling paint blistering, it probably is your gelcoat. But, by examining the substrate carefully, you can determine what is going on.
If you see a few blisters, then assume that you have a lot more that you cannot see. I have seen blisters on boats that just came out of the water and after the boat sits, the blisters sometimes (not always) go away. And you want to believe the problem doesn't exist, but it does. One person wrote about blisters in the keel to hull joint area. The blisters were most likely in the fairing compound used to smooth out that section. The keel which was either lead or metal didn't blister and the hull didn't, but the faring compound, which was more susceptible to moisture did. Perhaps a polyester and not an epoxy compound was used. Sometimes you see blisters in the waterline paint. If it was gelcoat, it might not blister, but if the wrong paint was applied (usually be the boat owner)then it could blister. Urethane paints are not guaranteed under the waterline. If your stripe sits submerged all season, and it is a Urethane paint, it will blister. Alwgrip or Awlcraft is wonderful paint, as long as it is above the waterline. Have antifouling paint creep above the waterline and then the waterline stripe or stripes should be painted above that. Epoxy paints are more waterproof, but they can't hold up to sunlight as well as urethanes and will chalk much more rapidly. Painting is another subject. Don't confuse gelcoat blisters with paint blisters. If you see your antifouling paint blistering, it probably is your gelcoat. But, by examining the substrate carefully, you can determine what is going on.
Responses to some questions
After reading some other responses I wanted to comment on a few. In most cases, depending on the system you use, you can (as is the case with Interprotect) paint the antifouling on within the time window allowed after your last coat of epoxy with out having to sand. If you are a racer, however, you will want to sand your epoxy very smooth before applying your fouling paint. After sandblasting or stripping the hull is anything but smooth and you need to apply fairing compounds to make it smooth. VC Systems has a product called VC Watertite which is a two part system that is easy to mix, easy to apply and easy to sand and you can sand it sooner than most epoxy products. It used to be that epoxy fairing compounds were hard to mix, hard to spread on and very hard to sand and you had to wait overnight to do it. Remember temperature has a lot to do with when you can sand and how fast it will set up (hotter is quicker). Whatever system you use, follow the guidelines and don't deviate. VC Tar used to be the barrier coat of choice. While it is a great product, it takes too long to cure and so it takes too long to do the job and if you put lift slings on the hull before the epoxy completely cured, you would leave sling imprints. Epoxies like Interprotect dry fast and hard and you can lift the boat with a sling much sooner without telltale imprints. To prevent blisters on a new boat, or a boat with no antifouling paint that has yet to get them, you must thoroughly clean all waxes off the hull and thoroughly sand the gelcoat to a frosty finish for a good tooth. Then clean again and apply your barrier coat. Any shiny, unsanded places on the hull will result in the paint coming off down the pike sometime. Do it right the first time. Some new boat manufacturers are now guaranteeing their hulls from blisters depending on the type of resins used in the process or some apply their own epoxy barrier coats. I have, however, seen some manufactures not apply this initial barrier coat properly so that it falls off, or they don't apply enough coats to properly protect the hull. Just because they say they have a barrier coat applied, doesn't mean they did it right (unfortunately).
After reading some other responses I wanted to comment on a few. In most cases, depending on the system you use, you can (as is the case with Interprotect) paint the antifouling on within the time window allowed after your last coat of epoxy with out having to sand. If you are a racer, however, you will want to sand your epoxy very smooth before applying your fouling paint. After sandblasting or stripping the hull is anything but smooth and you need to apply fairing compounds to make it smooth. VC Systems has a product called VC Watertite which is a two part system that is easy to mix, easy to apply and easy to sand and you can sand it sooner than most epoxy products. It used to be that epoxy fairing compounds were hard to mix, hard to spread on and very hard to sand and you had to wait overnight to do it. Remember temperature has a lot to do with when you can sand and how fast it will set up (hotter is quicker). Whatever system you use, follow the guidelines and don't deviate. VC Tar used to be the barrier coat of choice. While it is a great product, it takes too long to cure and so it takes too long to do the job and if you put lift slings on the hull before the epoxy completely cured, you would leave sling imprints. Epoxies like Interprotect dry fast and hard and you can lift the boat with a sling much sooner without telltale imprints. To prevent blisters on a new boat, or a boat with no antifouling paint that has yet to get them, you must thoroughly clean all waxes off the hull and thoroughly sand the gelcoat to a frosty finish for a good tooth. Then clean again and apply your barrier coat. Any shiny, unsanded places on the hull will result in the paint coming off down the pike sometime. Do it right the first time. Some new boat manufacturers are now guaranteeing their hulls from blisters depending on the type of resins used in the process or some apply their own epoxy barrier coats. I have, however, seen some manufactures not apply this initial barrier coat properly so that it falls off, or they don't apply enough coats to properly protect the hull. Just because they say they have a barrier coat applied, doesn't mean they did it right (unfortunately).
Lots of blisters
I got my 79 O'day 22 Feb 06 was in the water at Port Charlotte, Fla with some hurricane Charlie damage, thats at least 1 1/2 years in water, with fixable damage above waterline. I knocked the barnacles off while standing in 3 ft of water in a slip open to Charlotte Harbor and the barnacles were almost size of a quarter, that may tell some of you folks how long it was in the water. Back home in Asheville NC I blocked the boat and trailer up high enough to to work below the waterline. Useing a 3/8 corded drill and a 2 inch cutting disk in the chuck, which leaves a nice slope for the thickened epoxy to stick to being careful not to grind to deep just enough to clean off the loose material. There were hundreds of blisters, many were pea size to quarter size and those that were pingpong ball size and larger I cut fiber glass mat to cover each one and epoxied it in. I had several the size of a hard ball and soft balls which I put more than one layer of mat and epoxy at the same time before the epoxy started to set, whew, you gotta be fast. On these larger blisters, I got inside the boat, removed the foam flotation bats and I could see light thru the epoxied blisters, and these I cut even larger pieces of mat and epoxied them over inside the hull. I then filled all the blisters with thickened epoxy and sanded the hull smooth and painted the bottom with 3 coats of Petit Unepoxy. David S.
I got my 79 O'day 22 Feb 06 was in the water at Port Charlotte, Fla with some hurricane Charlie damage, thats at least 1 1/2 years in water, with fixable damage above waterline. I knocked the barnacles off while standing in 3 ft of water in a slip open to Charlotte Harbor and the barnacles were almost size of a quarter, that may tell some of you folks how long it was in the water. Back home in Asheville NC I blocked the boat and trailer up high enough to to work below the waterline. Useing a 3/8 corded drill and a 2 inch cutting disk in the chuck, which leaves a nice slope for the thickened epoxy to stick to being careful not to grind to deep just enough to clean off the loose material. There were hundreds of blisters, many were pea size to quarter size and those that were pingpong ball size and larger I cut fiber glass mat to cover each one and epoxied it in. I had several the size of a hard ball and soft balls which I put more than one layer of mat and epoxy at the same time before the epoxy started to set, whew, you gotta be fast. On these larger blisters, I got inside the boat, removed the foam flotation bats and I could see light thru the epoxied blisters, and these I cut even larger pieces of mat and epoxied them over inside the hull. I then filled all the blisters with thickened epoxy and sanded the hull smooth and painted the bottom with 3 coats of Petit Unepoxy. David S.
acne
I bought my 30' '88 Hunter 2 years ago with pox. She has no less than a thousand small eraser head size blisters. The surveyer said she'd probably had them for years and is mostly cosmetic, to keep an eye on them next haul out, but not to be too concerned about them - no boat ever sank from blisters and if you re-gel, you could get them again. I put on new bottom paint and keel fairing just after buying it and is holding up well, so another year on the paint. Next year, I do plan on letting the yard sand blast several layers of old paint off and opening up the blisters, letting them dry out for a couple of months, applying a good barrier coat and repainting. Hmmm, up to a 1,000 lbs of water! Maybe I can put those davits on without raising the waterline? Anyway, great subject, especially since there are certainly two sides - don't worry too much, and be very worried.
I bought my 30' '88 Hunter 2 years ago with pox. She has no less than a thousand small eraser head size blisters. The surveyer said she'd probably had them for years and is mostly cosmetic, to keep an eye on them next haul out, but not to be too concerned about them - no boat ever sank from blisters and if you re-gel, you could get them again. I put on new bottom paint and keel fairing just after buying it and is holding up well, so another year on the paint. Next year, I do plan on letting the yard sand blast several layers of old paint off and opening up the blisters, letting them dry out for a couple of months, applying a good barrier coat and repainting. Hmmm, up to a 1,000 lbs of water! Maybe I can put those davits on without raising the waterline? Anyway, great subject, especially since there are certainly two sides - don't worry too much, and be very worried.
NOT CONCERNED
Hello All, I bought my first boat, an Oday 39, two years ago. when it was hauled for prepurchase survey it was found to have boat pox. average of six blisters per square foot about dime to quater size over the entire hull. surveyor broke one open to find it had liquid inside with certain smell indicative of being into the laminate. she recommendend a blister profile which is to shave down about a square foot area to see how deep the blisters go or to take hull core samples. we went with the core samples and pulled two one inch diamter plugs in spots where there was a blister and sent them to a lab. report came back that blisters were only into first laminante, that the rest of laminates appeared healthy and that there was no need for concern at this time. being that my surveyor was very experienced and had worked for many years at ABYC developing ABYC specs I had allot of faith in her. she told me just to monitor the situation every year. so I bought the boat and am confident I have a very sound hull. will do a blister profile some time down the road to see if the blisters have gone any deeper, and I don't intend on repairing any of them as long as the situation does not progress. funny thing is that at last haul out the blisters did not show at all. I examined the hull right out of the water and could not find one. if any one can comment on why I could not see them I would appreciate it. Happy Sailing Capt. Jules Miami, FL S/V Providencia
Hello All, I bought my first boat, an Oday 39, two years ago. when it was hauled for prepurchase survey it was found to have boat pox. average of six blisters per square foot about dime to quater size over the entire hull. surveyor broke one open to find it had liquid inside with certain smell indicative of being into the laminate. she recommendend a blister profile which is to shave down about a square foot area to see how deep the blisters go or to take hull core samples. we went with the core samples and pulled two one inch diamter plugs in spots where there was a blister and sent them to a lab. report came back that blisters were only into first laminante, that the rest of laminates appeared healthy and that there was no need for concern at this time. being that my surveyor was very experienced and had worked for many years at ABYC developing ABYC specs I had allot of faith in her. she told me just to monitor the situation every year. so I bought the boat and am confident I have a very sound hull. will do a blister profile some time down the road to see if the blisters have gone any deeper, and I don't intend on repairing any of them as long as the situation does not progress. funny thing is that at last haul out the blisters did not show at all. I examined the hull right out of the water and could not find one. if any one can comment on why I could not see them I would appreciate it. Happy Sailing Capt. Jules Miami, FL S/V Providencia
Blisters generally overrated
I have owned three fiberglass boats now: a '79 Paceship PY23, a '78 Pearson 26 One-design, and currently a '79 Pearson 32. The Paceship and the P32 had barrier coats applied by a PO, and all three boats had blisters. Don't know if it was coincidence or not, but the barrier coated boats tended toward dozens of penny-sized lumps, while the uncoated boat had hundreds of BB-size pimples. In no case did I ever feel like the integrity of the hull was threatened, it was just one more chore to perform while doing a bottom job. What I would do is grind out the blisters, let them dry a day or two (in south LA nothing every really gets dry), fill with West System fairing compound, sand out and apply bottom paint. None of the boats has sunk yet. Based on my experience, the people who want to charge you untold thousands to strip the gelcoat off your boat, let it dry for months, and put on miracle coatings are little more than snake-oil salesmen. Not so much because the coatings don't work, but because I think it's impossible to really dry out the laminate on an old boat, short of trucking it to the desert for a year or so. And also because I don't think the average blister crop in any way endangers the boat. Just my opinion.
I have owned three fiberglass boats now: a '79 Paceship PY23, a '78 Pearson 26 One-design, and currently a '79 Pearson 32. The Paceship and the P32 had barrier coats applied by a PO, and all three boats had blisters. Don't know if it was coincidence or not, but the barrier coated boats tended toward dozens of penny-sized lumps, while the uncoated boat had hundreds of BB-size pimples. In no case did I ever feel like the integrity of the hull was threatened, it was just one more chore to perform while doing a bottom job. What I would do is grind out the blisters, let them dry a day or two (in south LA nothing every really gets dry), fill with West System fairing compound, sand out and apply bottom paint. None of the boats has sunk yet. Based on my experience, the people who want to charge you untold thousands to strip the gelcoat off your boat, let it dry for months, and put on miracle coatings are little more than snake-oil salesmen. Not so much because the coatings don't work, but because I think it's impossible to really dry out the laminate on an old boat, short of trucking it to the desert for a year or so. And also because I don't think the average blister crop in any way endangers the boat. Just my opinion.
Keep your bilge dry!
One thing to keep in mind about blisters and especially when applying a barrier coat is that you MUST keep the bilge dry! Two studies were done at the at the University of Rhode Island at the request of the U.S. Coast Guard. One was to find the cause of blisters and the second was to look for a fix. The first study found that one major cause of blisters was not the water on the outside of the boat but the water on the inside... in the bilge. Polyester resin is not molecularly "water tight" as one may think and water can penetrate through the laminate on a molecular level from the bilge and get trapped between the gelcoat and the laminate. Just as water can penetrate the gelcoat and be caught between the laminate and gelcoat. Since the gelcoat is porous it will allow the bilge water through in some instances. However, a barrier coat will trap that moisture that is migrating from the bilge. That's why you see blisters on epoxy coated bottoms. The second study was to find a cure. Most blisters are harmless and only cosmetic. If you feel the need to repair the blisters, it was actually found that an alkyd enamel was just as effective as epoxy coating at staving off new blisters. It was also found that the FRP panels coated with the alkyd enamel had less sever blistering than the epoxy coating. It was thought that the alkyd enamel actually let the hull "breath." I have used the enamel on a blistered hull four years ago and no new blisters have occurred. Of course I also make sure that the bilge is kept dry. It is also a good idea to use the enamel on the inside of the hull as well (if it isn't gel coated or painted already) to help with water penetration from the inside out.
One thing to keep in mind about blisters and especially when applying a barrier coat is that you MUST keep the bilge dry! Two studies were done at the at the University of Rhode Island at the request of the U.S. Coast Guard. One was to find the cause of blisters and the second was to look for a fix. The first study found that one major cause of blisters was not the water on the outside of the boat but the water on the inside... in the bilge. Polyester resin is not molecularly "water tight" as one may think and water can penetrate through the laminate on a molecular level from the bilge and get trapped between the gelcoat and the laminate. Just as water can penetrate the gelcoat and be caught between the laminate and gelcoat. Since the gelcoat is porous it will allow the bilge water through in some instances. However, a barrier coat will trap that moisture that is migrating from the bilge. That's why you see blisters on epoxy coated bottoms. The second study was to find a cure. Most blisters are harmless and only cosmetic. If you feel the need to repair the blisters, it was actually found that an alkyd enamel was just as effective as epoxy coating at staving off new blisters. It was also found that the FRP panels coated with the alkyd enamel had less sever blistering than the epoxy coating. It was thought that the alkyd enamel actually let the hull "breath." I have used the enamel on a blistered hull four years ago and no new blisters have occurred. Of course I also make sure that the bilge is kept dry. It is also a good idea to use the enamel on the inside of the hull as well (if it isn't gel coated or painted already) to help with water penetration from the inside out.
A couple hundred at least
The P.O. of my '88 H23 kept the boat in warm fresh water for several years. When I hauled it to referesh the bottom paint, I noticed a LOT of blisters, ranging in size from a pencil eraser to the palm of my hand. The yard said not to worry. WhenI hauled the boat three years later, the blisters were worse. I hauled the boat that September and left it in the backyard on the trailer for six months to dry out. The blisters were ground back to clean dry laminate, then I sanded the hull and applied two coats of Interprotect 1000 (epoxy) barrier coat. Then I filled the blister holes with Interlux fairing compound (some large areas had to be done twice to build up enough excess material to maintain the curve of the hull) and faired the hull. I followed that with five coats of Interlux Epiglass epoxy, washing with denatured alcohol and sanding between coats. After that it was two coats of VC Tar and three coats of VC17. It took nine momths, but I haven't had a problem since. Peter H23 "Raven"
The P.O. of my '88 H23 kept the boat in warm fresh water for several years. When I hauled it to referesh the bottom paint, I noticed a LOT of blisters, ranging in size from a pencil eraser to the palm of my hand. The yard said not to worry. WhenI hauled the boat three years later, the blisters were worse. I hauled the boat that September and left it in the backyard on the trailer for six months to dry out. The blisters were ground back to clean dry laminate, then I sanded the hull and applied two coats of Interprotect 1000 (epoxy) barrier coat. Then I filled the blister holes with Interlux fairing compound (some large areas had to be done twice to build up enough excess material to maintain the curve of the hull) and faired the hull. I followed that with five coats of Interlux Epiglass epoxy, washing with denatured alcohol and sanding between coats. After that it was two coats of VC Tar and three coats of VC17. It took nine momths, but I haven't had a problem since. Peter H23 "Raven"
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