I have long wondered about the wisdom, or lack thereof, of putting a barrier coat on one's fiberglass boat. It seems to me that blisters form due to moisture trapped within the laminate of a fiberglass hull or deck that migrates to the surface. Unless a boat is stripped entirely of the gel coat and enough laminate gouged outto thoroughly dry out the trapped moisture -- a very time consuming and expensive undertaking, particularly considering the need to replace what you stripped -- applying a barrier coat would seem to be a total waste of time, money and effort. I can hardly think of a boat that would justify the cost. Added to that, to the best of my knowledge, most fiberglass hulls/decks have two surfaces: if the trapped moisture cannot migrate out one way (i.e., to the outside of your boat), my guess is that it would migrate the other way (i.e., to the inside of your hull). A barrier coat would not be of much help in that case. What real purposes due barrier coats have other than to enrich the makers of these products? An inquring mind wants to know.
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Two Answers
Pete, There are two reasons to apply a barrier coat. The first might be just to seal over any type of previous coating with which a paint to be applied would not be compatible. e.g. differing makes of anti-foul. The second reason might be to improve osmosis resistance. To be effective the hull needs to be DRY. This means right through the laminate. Then, by applying several coats of a water impervious paint, further water ingress is prevented - you hope! Osmosis is where water forces its way into a hull through the pores in the gel coat. It can develop quite a force and has no trouble in bursting gel coat off laminate. I had an interesting demonstration of osmosis. My kids brought over some Helium filled balloons for my birthday party. After the party I just left them. In due course the gas migrated out of the balloon until the it went absolutely flat. ie. far beyond where there was any pressure in it. It was as if all the gas had been sucked out. Which is exactly what had happened. Sadly, in boats it works in the opposite direction.
Pete, There are two reasons to apply a barrier coat. The first might be just to seal over any type of previous coating with which a paint to be applied would not be compatible. e.g. differing makes of anti-foul. The second reason might be to improve osmosis resistance. To be effective the hull needs to be DRY. This means right through the laminate. Then, by applying several coats of a water impervious paint, further water ingress is prevented - you hope! Osmosis is where water forces its way into a hull through the pores in the gel coat. It can develop quite a force and has no trouble in bursting gel coat off laminate. I had an interesting demonstration of osmosis. My kids brought over some Helium filled balloons for my birthday party. After the party I just left them. In due course the gas migrated out of the balloon until the it went absolutely flat. ie. far beyond where there was any pressure in it. It was as if all the gas had been sucked out. Which is exactly what had happened. Sadly, in boats it works in the opposite direction.
I had the same thought when I bought my boat.
I had no blistering problems. In fact after I stripped it down to the gel coat I found it in "like new condition". I struggled with the decision to do that expensive and difficult job. I finally consulted several experienced boat maintainance folks (all very willing to give helpfull advice) and the general consus was if it ain't broke don't fix it. Some agreed with my feeling (and yours I think)that it may create a problem or make it worse. All of them also agreed that since I'm out of the water 50% of the time while wintering it would be enough to dry the hull and prevent any problem from starting. Being in Ches Bay it sounds like you winter haul too. The folks in the far south have it worse with warm water and a year round season (I mean for blisters). But I agree there doesn't seem to be a clear consensus. Moisture ingress can happen from the inside too. How about a perpetually wet bildge? Lots of atricles and opinions out there. Rob
I had no blistering problems. In fact after I stripped it down to the gel coat I found it in "like new condition". I struggled with the decision to do that expensive and difficult job. I finally consulted several experienced boat maintainance folks (all very willing to give helpfull advice) and the general consus was if it ain't broke don't fix it. Some agreed with my feeling (and yours I think)that it may create a problem or make it worse. All of them also agreed that since I'm out of the water 50% of the time while wintering it would be enough to dry the hull and prevent any problem from starting. Being in Ches Bay it sounds like you winter haul too. The folks in the far south have it worse with warm water and a year round season (I mean for blisters). But I agree there doesn't seem to be a clear consensus. Moisture ingress can happen from the inside too. How about a perpetually wet bildge? Lots of atricles and opinions out there. Rob
Barrier coating
Had my underwater hull sandblasted and coated some years ago because my boat is an '81 and I wanted to know what I had for a hull. Good thing: small clusters of pinhead size blisters, so I know what I have. Bad thing: cost a bit of change. I do not regret it, however, because even though it was overkill I am confident of the condition of my underwater hull. By the way, if this process is done with care there is no need to destroy the gel coat. Regards, Jim.
Had my underwater hull sandblasted and coated some years ago because my boat is an '81 and I wanted to know what I had for a hull. Good thing: small clusters of pinhead size blisters, so I know what I have. Bad thing: cost a bit of change. I do not regret it, however, because even though it was overkill I am confident of the condition of my underwater hull. By the way, if this process is done with care there is no need to destroy the gel coat. Regards, Jim.
I have two views. On my previous boat which was four years old when bought there was considerable blistering from pinhead to 3" diameter. On the basis that gelcoat is porous I decided that sealing it off with epoxy might be some help. The hull was sanded and epoxy applied. It was useless and for the six years that I owned her I treated on average 10-15 blisters per year on the annual haul out. They were ground out, dried with a hair dryer and filled with epoxy. Flash forward to 2004 when I bought a new H33. I figured that with vacuum bagging and five year anti blister warranty maybe the days of blistering were over. However I still dont like the idea of having a porous material on the outside of the hull. It just seems to be crazy, so I had the Barrier coat for no other reason than the comfort of knowing that the hull was waterproof. Only time will tell !
Molecules
It is my understanding that once the water molecules have "osmosed" past the gelcoat and are in the laminate, they can react chemically with unhardened resin and create molecules that are too large to pass back through the gelcoat. Thus, they are forever trapped in the blister, unless it is cut open and cleaned out. I do know that when you cut into a blister, the liquid inside is usually not clear, like water, but rather it can range from a dark gray to a rust color. A guy who worked in a boatyard once told me not to worry much about them unless they are pretty large or unless you are racing and want a smooth hull. He said, "no boat ever sank because it had a bunch of small blisters."
It is my understanding that once the water molecules have "osmosed" past the gelcoat and are in the laminate, they can react chemically with unhardened resin and create molecules that are too large to pass back through the gelcoat. Thus, they are forever trapped in the blister, unless it is cut open and cleaned out. I do know that when you cut into a blister, the liquid inside is usually not clear, like water, but rather it can range from a dark gray to a rust color. A guy who worked in a boatyard once told me not to worry much about them unless they are pretty large or unless you are racing and want a smooth hull. He said, "no boat ever sank because it had a bunch of small blisters."
I doubt that there is a knowable answer
Having worked in a chemical plant that made a variety of resins including polyester and flame retardant polyester, all I can say is that there are lots of manufacturing variables. Most boats are made using polyester resin in the fiberglass. We made the stuff 100,000 pounds at a time. The resin characteristics would vary with raw materials, temperature, time of year, time of day, operator technique, equipment maintenance, accidental additions and downright mistakes. I did a lot of the testing and made some process control decisions during and after the cooking of these products. There was a lot of variability in the same product and it was not always something that we could control or correct. It all was eventually sold - good or bad. I know that a lot of the so called fireproof resins went into boats which had lots of blister problems. When a boat is manufactured, the things which will affect the final product also will vary a lot. Many of the same things will change the character of the fiberglass when it is manufactured. Temperature, time of year, time of day, operator technique, thickness of the laminate, type and quality of the glass, quality of the initiator, proper mixing of the resin, solvents, intended and unintended additives, equipment maintenance, ..... It is a miracle to me that the boats turn out consistently as well as they do. Whatever it is that really causes blisters, it is clear that some boats get them and some do not. If you do not have them in a year, why worry about it? If you are getting a new boat, look at what the manufacturer has made recently, check out their warranties and make a choice.
Having worked in a chemical plant that made a variety of resins including polyester and flame retardant polyester, all I can say is that there are lots of manufacturing variables. Most boats are made using polyester resin in the fiberglass. We made the stuff 100,000 pounds at a time. The resin characteristics would vary with raw materials, temperature, time of year, time of day, operator technique, equipment maintenance, accidental additions and downright mistakes. I did a lot of the testing and made some process control decisions during and after the cooking of these products. There was a lot of variability in the same product and it was not always something that we could control or correct. It all was eventually sold - good or bad. I know that a lot of the so called fireproof resins went into boats which had lots of blister problems. When a boat is manufactured, the things which will affect the final product also will vary a lot. Many of the same things will change the character of the fiberglass when it is manufactured. Temperature, time of year, time of day, operator technique, thickness of the laminate, type and quality of the glass, quality of the initiator, proper mixing of the resin, solvents, intended and unintended additives, equipment maintenance, ..... It is a miracle to me that the boats turn out consistently as well as they do. Whatever it is that really causes blisters, it is clear that some boats get them and some do not. If you do not have them in a year, why worry about it? If you are getting a new boat, look at what the manufacturer has made recently, check out their warranties and make a choice.
Blisters r a Serious Problem
American and European boat builders started applying barrier coats in 1984. By 1985 it was almost universal. The reason was the high number of complaints from customers whose boats were blistering and the very high cost of professional repairs. The bottom of any boat more than 12 years old should be stripped, including the old barrier coat, allowed to dry out over the winter and new barrier coat and bottom coat applied. I am stripping mine this weekend. For about $200 in materials and some elbow work I am protecting myself from a $3,000 repair job. Good investment.
American and European boat builders started applying barrier coats in 1984. By 1985 it was almost universal. The reason was the high number of complaints from customers whose boats were blistering and the very high cost of professional repairs. The bottom of any boat more than 12 years old should be stripped, including the old barrier coat, allowed to dry out over the winter and new barrier coat and bottom coat applied. I am stripping mine this weekend. For about $200 in materials and some elbow work I am protecting myself from a $3,000 repair job. Good investment.
Arthur....
I personally think that if "stripping" means peeling your gel coat, you may still have problems. Moisture trapped under the gelcoat and within the laminate will not "dry out over the winter" by itself. I believe that you would have to remove the laminate itself if you really want to dry out your hull. I suppose it may also be possible to get rid of some of this trapped moisture by tenting your boat and keeping heat lamps on it constantly over the winter. The real question continues to be: what justifies what? My sense of all this is that if you have a small number of blisters, gouge them out, dry the holes, fill them with epoxy and then go sailing. If your boat has the pox all over, get used to them or get another boat. As someone said, he could recall no boat ever sinking due to blisters....
I personally think that if "stripping" means peeling your gel coat, you may still have problems. Moisture trapped under the gelcoat and within the laminate will not "dry out over the winter" by itself. I believe that you would have to remove the laminate itself if you really want to dry out your hull. I suppose it may also be possible to get rid of some of this trapped moisture by tenting your boat and keeping heat lamps on it constantly over the winter. The real question continues to be: what justifies what? My sense of all this is that if you have a small number of blisters, gouge them out, dry the holes, fill them with epoxy and then go sailing. If your boat has the pox all over, get used to them or get another boat. As someone said, he could recall no boat ever sinking due to blisters....
Blisters and barrier coats - some basic info
Before you start removing gelcoat or applying epoxy barrier coats (or both!) I think a little fact-finding is in order. Here's a link to one of the better explanations of osmotic blistering that I've read in the last four years. It's worth a read. http://www.oceanmarineservices.com/osmotic_blistering.htm I completed a blister repair and barrier coat job on my hull about three years ago. The previous owner left the boat in the St Johns River (warm, fresh water) for five years straight. I didn't know and left it in for one more year. When the boat was finally hauled for maintenance, I found a large number of blisters, some of which were as large as the palm of my hand. Luckily, almost all of them were between the gelcoat and the laminate. Every single blister was punctured, ground back to dry laminate and washed. The boat then sat under a tent for four months to finish drying out. Every ground-back area was cleaned with acetone, coated with epoxy, filled with epoxy-based filler and sanded smooth. The entire hull to three inches above the waterline was then painted with four coats of epoxy (washing carefully and sanding between coats) followed by primer and bottom paint. Not a single blister has appeared since then. Based on these experiences, my research leading up to the project and the marine surveyor's article, here's my two cents,.. If it ain't broke, don't fix it. Barrier coating should only be applied if you have a serious blistering problem and decide to deal with it (some people don't). A brand new hull doesn't need a barrier coat and even if it did, you certainly don't need to grind off all the gelcoat to apply it. Resin technology and hull construction techniques have improved dramatically over the last six to eight years. If you do attempt a program of blister repair and barrier coating, don't skimp. Invest the time to dry the hull, use quality materials and apply them properly. To be absolutely sure, I did the work myself and it took six months. This is not the type of job you ever want to do again. Good luck. Peter H23 "Raven"
Before you start removing gelcoat or applying epoxy barrier coats (or both!) I think a little fact-finding is in order. Here's a link to one of the better explanations of osmotic blistering that I've read in the last four years. It's worth a read. http://www.oceanmarineservices.com/osmotic_blistering.htm I completed a blister repair and barrier coat job on my hull about three years ago. The previous owner left the boat in the St Johns River (warm, fresh water) for five years straight. I didn't know and left it in for one more year. When the boat was finally hauled for maintenance, I found a large number of blisters, some of which were as large as the palm of my hand. Luckily, almost all of them were between the gelcoat and the laminate. Every single blister was punctured, ground back to dry laminate and washed. The boat then sat under a tent for four months to finish drying out. Every ground-back area was cleaned with acetone, coated with epoxy, filled with epoxy-based filler and sanded smooth. The entire hull to three inches above the waterline was then painted with four coats of epoxy (washing carefully and sanding between coats) followed by primer and bottom paint. Not a single blister has appeared since then. Based on these experiences, my research leading up to the project and the marine surveyor's article, here's my two cents,.. If it ain't broke, don't fix it. Barrier coating should only be applied if you have a serious blistering problem and decide to deal with it (some people don't). A brand new hull doesn't need a barrier coat and even if it did, you certainly don't need to grind off all the gelcoat to apply it. Resin technology and hull construction techniques have improved dramatically over the last six to eight years. If you do attempt a program of blister repair and barrier coating, don't skimp. Invest the time to dry the hull, use quality materials and apply them properly. To be absolutely sure, I did the work myself and it took six months. This is not the type of job you ever want to do again. Good luck. Peter H23 "Raven"
Hey Peter- here's another link....
from the old plastics forum. It is now back in the Chandlery section. It is mix of personal observations, various write ups and the videos from the West System people.
from the old plastics forum. It is now back in the Chandlery section. It is mix of personal observations, various write ups and the videos from the West System people.
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