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Discussion Starter #1 (Edited)
My understanding is that hull blisters are the product of depolymerization of the
Polyester due to water exposure. This occurred due to resin formulas being changed during the mid-70s to reduce costs. Does anyone out there know what the original resins were? And if there's any information about what manufacturers changed resins and when that occurred. Were there any manufacturers that employed epoxy resins, exclusively.
 

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Try this. Your assumptions are a bit off. ALL hulls built of polyester resins prior to the introduction of vinylester resin and epoxy are subject to blisters. SOME of those polyester boats had more problems than others due to the quality of materials used in certain runs...like some of the Valiants and Beneteaus. (BTW...Benny recalled and fixed all their bad hulls.). Epoxy was not used in production boat building until around 2000. Vinylester was a late 80's introduction in SOME boats.
http://www.zimmermanmarine.com/docs/blisters%201.pdf

Hull Blisters: Know the Enemy
 

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Some more recent boats have been made with oven cured epoxy resins, but most are still being made of polyester and vinylester resin due to their lower costs.
 

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I have spent many hours on the internet researching this subject, there are plenty of opinions and some facts, but the truth is that no one currently knows the cause or the cure. It's a pity, since it's a GRP pox that can prove very expensive.
Baz
 

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Discussion Starter #5
Thanks camaraderie. To recap

I think you answered my question FRP, GRP, Fiberglas are all polyester resin-based glass reinforced plastics until 1980 with the introduction of vinyl ester resin on some boats. In 2000 epoxy started being used, but is not widespread because of the expense.
 

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OSMOSIS TESTING
( a highly simplified explanation )

If I knew what an osmosis test was I could be doing a lot more business as I get asked for it all the time. Dock talkers often use "blisters" and "osmosis" as interchangeable terms however, there are different types, causes and degrees of blisters and using the word "osmosis" just confuses the issue. I am often asked if I can perform an osmosis test to which my response is " What's an osmosis test ?". This response is met with a blank look as the people asking the question really don't know what they are asking.

This is one of the reasons I dislike the word "osmosis" as applied to boats, it has become a generic term to describe all types of blisters and moisture content in fiberglass hulls cored and uncored. Strictly speaking for osmosis to occur you need fluid on both sides of a membrane. If you have this situation on a boat, you have more problems than a few blisters. What you are really encountering is simply water soaking into a porous material. Polyester, epoxy and vinylester resins are not waterproof, they are hygroscopic ie. They can absorb and retain water! (less so with epoxy and vinylester). I have heard many convoluted definitions of osmosis in attemps to justify the use of the word but what we really have is simply a process of absorption.


OSMOSIS: The tendency of fluid substances, if separated by a porous, membrane to filter through it and become equally diffused.

So lets forget about the semantics and get to the issue................

There are many of causes of blistering, To list a few ....... trapped moisture during moulding, undercured resin, overcured resin, aerated resin, incorrect timing of subsequent layers, absorbent fillers, voids, trapped moisture in core materials, stale catalyst, emulsion bound mat, dusty mould, hygroscopic dust, cold mould, inadequately mixed resin, uncontrolled temperature and humidity levels during moulding process, uncontrolled temperature and humidity of raw materials in shipping, orthophtalic (cheap) resins. OK .... enough ! If I really thought about it I am sure I could come up with more but lets just say this, it is an extremely complex issue and "osmosis" just does not cover it. all you need to know is about blisters.

If you insist on calling osmosis then it follows that all fiberglass boats have it !

NO VOIDS = NO BLISTERS (maybe) : There are dozens of reasons for voids in a laminate (some chemical) and they can range from tiny champagne size bubbles to several square feet although most are less than 1/2" in diameter. The average laminate may be 8-15 layers of various types of glass fabric made up of millions of miles of microscopically thin glass strands wetted out with resin. It is unreasonable to assume that all voids will be filled whether the wet-out is accomplished by five guys with rollers or one of the admittedly better (but not perfect) vacuum bag processes. All fiberglass layaups have voids, some more than others. The higher the void content, bigger the voids and the more likely and earlier you will see blisters.

A typical 30' , uncored sailboat hull can absorb about 30lbs. of water or roughly 3% maximum weight of the laminate. The glass fibers do not absorb any water and the resin is chemically incapable of absorbing more than 3% so theoretically 3% water content is sturation point of the material (voids excluded). As all polyester reinforced glass fiber and gelcoats are water permeable to some degree, all fiberglass boats left in water long enough will absorb water and probably develop blisters. This is rarely a structural issue (at least in our lifetime) although it can drive the sailboat racers nuts !

If the hull is cored with balsa or the laminate is all chopped strand (read - very cheap boat) then you may have a more serious and expensive issue to deal with as the balsa rots when wet and in the case of chopped strand fiber, the millions of exposed fiber ends wick water like so many straws.

The more common gelcoats are simply pigmented polyester resin of varying levels of quality and these pigments combined with the aeration caused by spraying the product into the mold can make it more permeable than the resin used in the laminate and therefore most blisters appear in the gelcoat. These blisters are usually small (1/8 - 1/4" dia.) and round in shape. While this does have an effect of the sale value of the vessel it is rarely a cause for concern.

Under the gelcoat is usually a "skinout" mat of chopped strand glass fibers that does not contribute much to the strength of the hull but is used primarily to hide the basket weave pattern of the heavier woven fiber which (hopefully) makes up most of the laminate. When water passes through the gelcoat it may wick up the chopped strand fibers of the "skinout" mat. These blisters are usually small, elongated and again not a major concern.

Water that has passed through the gelcoat and skinout mat into the structural laminate may combine with soluble elements that may occur in the voids. These elements could be uncatalysed resins, silane, glycol or salts (not the table variety) or any of the other chemical soup of ingredients that results from the resin curing (or uncured) process. When water combines with these molecules a new, usually larger molecule forms (hydrolysis), thus preventing escape of the fluid since the molecule is now bigger than the microscopic hole it came in through.

HYDROLYSIS: A chemical process by which the oxygen or hydrogen in water combines with an element or some element of a compound to produce a new compound.

As these newer, larger molecules multiply deep in the laminate they can get big enough to start to pushing apart the various layers of the laminate as the resin dissolves. This can be a serious issue, it is however relatively rare.

Put on a pair of safety goggles and puncture a few blisters. If they are dry or release a clear fluid, you likely do not have the serious type of blister. If an acidic vinegar like fluid appears this could be the more serious "Hydrolysis" type blister. Be careful as some of these blisters contain fluids under tremendous pressure. If the blister is very large and cannot be punctured with an ice-pick, it is likely very deep in the laminate, in this case drilling a hole for closer inspection may be warranted.

THE CURE? Sorry..... regardless of the chemical companies hype there is no cure. You can only delay the inevitable but a very high percentage of blistered boats will still outlast you. I have surveyed one local boat three times over the last 10 years and each time it was getting another $10k "epoxy bottom job". I refused to survey it a fourth time because a well respected shop was about to do it again using the same improper techniques as the previous three jobs done by others. Whoever buys this 42' motor yacht will be doing it again soon (if there is any laminate left).
Small blisters in the gelcoat may be repaired by sanding, drying and applying an epoxy or vinylester bottom coat. This may help the resale value of your boat. Blisters in the skinout mat can be repaired by the same method but with much more aggressive sanding and perhaps some patching. The larger hydrolysis blisters require complete removal of the gelcoat and probably the skinout mat and perhaps a layer of the laminate (perhaps in local areas or over the entire hull in which case new cloth may be needed). The hull must then be dried to the point where the epoxy or vinylester bottom coat will adhere and washed frequently during the drying process to wash off as much of the hydrolytic fluid as possible. This fluid and water may weep from the hull for weeks, months or even years so washing is crucial to providing a clean surface to ensure the adhesion of the new barrier coating.
This can be a bit of a gamble. Many bottom coats fail because the hull was not dried or washed properly. I have seen boats put under heat lamps for six months before bottom coating and new blisters appeared within a few years. The moisture is so deep in the laminate at a molecular level that it is not easily evacuated. A new system of applying heat under vacuum holds promise for drying hulls but for the most part it's still a gamble.

Give this careful consideration before plunking down $5,000.00 - $10,000.00 - $20,000.00 or more for a bottom job and always ask for a written guarantee (unlikely). Consult an Accredited Marine Surveyor® before spending you're hard earned money.
 

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I just can't believe that so many GRP boat builders can be a fault for building boats that later "Blister" There is obviously something intrinsically wrong with the process that has not been identiified. Or if it has no one is telling. Whilst epoxy might well be the answer, it doesn't seem to help all the GRP so far built. I am considering the purchase of a 197X Contessa, but I don't want a bill for many thousands of dollars in the next few years, that would be more than I paid for the boat. So whats the answer? Scrap all the boat? Pay surveyors to tell me what I already know? At least with a wooden boat I can do localized repairs fairly easily.
Baz
 

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Would you scrap your wife is she developed a few blisters on her ........ :)
it dosn't mean she's going to sink
 

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Would you scrap your wife is she developed a few blisters on her ........ :)
it dosn't mean she's going to sink
My wife scrapped me a year ago! Thank god, no blisters, just open heart surgery. But I'm better off. I've been researching blisters, as you know there is a huge thread here about it. But no proven answers, lots of opinions. To buy or not to buy? Actually I can do all the boat work myself. Rent a stripper and recoat the bottom with epoxy, yes, but will this prevent the problem from happening again? Seem not.
Barry
 

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Thanks camaraderie. To recap

I think you answered my question FRP, GRP, Fiberglas are all polyester resin-based glass reinforced plastics until 1980 with the introduction of vinyl ester resin on some boats. In 2000 epoxy started being used, but is not widespread because of the expense.
All correct EXCEPT that Vinylester really wasn't used anywhere until the LATE 80's...but was common by the mid-90's.
 

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I just filled what I call gel coat imperfections - places where the soda blasting exposed convexities and concavities in the 1983 hull. None held water, no elevated moisture. I sanded down the convex and filled the concave. It was labor intensive as the imperfections nubered in the tens of thousands, but in the end really only superficial. I could have done nothing and been fine.
 

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These aren't really osmotic blisters, they are what you called them or gel coat voids.

I just filled what I call gel coat imperfections - places where the soda blasting exposed convexities and concavities in the 1983 hull. None held water, no elevated moisture. I sanded down the convex and filled the concave. It was labor intensive as the imperfections nubered in the tens of thousands, but in the end really only superficial. I could have done nothing and been fine.
 

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Just my observation over a number of years....a lot of fear and panic exists over blisters...and why not, it generates business. In most older boats and some new ones you may find some blisters...open them up, dry them, fill with expoxy, sand smooth, paint and go sailing. It's generally not a really big problem and you don't need to grind away a third of the boat's fiberglass and reglass to resolve them. That's a waste of money in most cases.
 

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Barrier Coating

I recently dug out several score of blisters ont a 1972 Morgan 27 that had been kept in the water much of it's life. The hull was thoroughly dried and then each pocket was coated with West System epoxy to the saturation point. With careful monitoring the "epoxified" pockets were filled with epoxy putty made with cabosil, phenolic balloons and milled 'glass fiber while the epoxy was still a little tacky. When that dried (overnight), I washed the amine blush (the greasy residue which is a by product of the epoxy cure) with dishwashing liquid, rinsed thoroughly with fresh water, sanded the pockets and applied Microlight fairing putty. After final sanding I then applied 6 coats of Interlux 2000E epoxy barrier coat as per the instructions. This was last year and I fully expect to have new pockets crop up as the years go by. I will deal with each one as they come.
My next step will be to strip the bilges with Marine PeelAway and coat the bilges with 3 coats of West System epoxy. I've heard that blistering can come from wet bilges as well as from outside water. I expect that this will be an ongoing addition to my regular maintainence program. The good news is that I have a boat that I paid $2400 for that would cost $40.000 to replace.
 

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SAMS, nice explanation. You put in simple words what took me a year on research and money wasted. Thanks !
 

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The problem has been identified!!!

I just can't believe that so many GRP boat builders can be a fault for building boats that later "Blister" There is obviously something intrinsically wrong with the process that has not been identiified.
Baz
It's called SALT WATER. It eats just about anything.
 

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I worked for a builder in NY for 11 years that fabricated megayachts as well as Navy and Coast Guard vessels. We used epoxy exclusively in place of polyester resin, particularly for any repair work. A rule of thumb is that epoxy, applied properly, will adhere tenaciously to either polyester or itself, whereas polyester with adhere to neither very well. It's also important to think of epoxy as the strongest most waterproof adhesive commonly used, while polyester is binding resin for fabricating inexpensive hulls and decks. Polyester is not an adhesive and it is relatively porous. Gel coat is merely tinted polyester resin. When you consider the amount of labor in the typical repair, the extra expense of epoxy becomes negligable. Do yourself a favor. Learn how to use epoxy, follow the directions, protect your skin and your lungs and make repairs that will out live you. Oh, and by the way, I've seen boats built in the 60s that were kept on freshwater lakes blister up terribly. Salt water is corrosive and electrolitic, but both salt or fresh will find it's way through polyester eventually. Don't forget to protect your bilges with 3 coats of epoxy too.
 

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For what it's worth I am a full time fly fishing guide who rows a 20ft drift boat. Over many miles the oar blades that are oak and reinforced with polyester resin and glass totally delaminated. I replaced with glass and West Epoxy. Whilst they have held up better that the orginal Sawyer finish, they still peeled in a few places and the glass looks like it's starting to delaminate again. Epoxy better? Well a definite maybe.
Barry
 

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This is especially true for structural repairs of older fiberglass boats, where most of the styrene sites have cured and first-order linking is very unlikely to occur, so that the adhesive strength of the resin used for repairs is the primary factor in how strong the repair is. going to be.

I worked for a builder in NY for 11 years that fabricated megayachts as well as Navy and Coast Guard vessels. We used epoxy exclusively in place of polyester resin, particularly for any repair work. A rule of thumb is that epoxy, applied properly, will adhere tenaciously to either polyester or itself, whereas polyester with adhere to neither very well. It's also important to think of epoxy as the strongest most waterproof adhesive commonly used, while polyester is binding resin for fabricating inexpensive hulls and decks. Polyester is not an adhesive and it is relatively porous. Gel coat is merely tinted polyester resin. When you consider the amount of labor in the typical repair, the extra expense of epoxy becomes negligable. Do yourself a favor. Learn how to use epoxy, follow the directions, protect your skin and your lungs and make repairs that will out live you. Oh, and by the way, I've seen boats built in the 60s that were kept on freshwater lakes blister up terribly. Salt water is corrosive and electrolitic, but both salt or fresh will find it's way through polyester eventually. Don't forget to protect your bilges with 3 coats of epoxy too.
 
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