Osmotic Blistering

[shrew]

Here is an interesting read. I thought I'd throw it up here in case anyone was interested:

http://www.hartoftmarinesurvey.com/guide.html

 

[stubbsboogie]

Re: Osmotic Blistering

read that a while back while I was trying to think of what to do about the blisters on our old boat.
Good article.

 

[Home Cookin']

Re: Osmotic Blistering

interesting. although I read it over quickly, it sounds like blistering, any of the three types, occurs rather typically over a long time; that water has to be present (no mention of temperature); that, like music by Wagner, it's not as bad as it sounds. I suppose it's the equivalent of inevitable wood rot in a wooden hull boat of yesterday.

 

[lkbum]

Re: Osmotic Blistering

interesting. although I read it over quickly, it sounds like blistering, any of the three types, occurs rather typically over a long time; that water has to be present (no mention of temperature); that, like music by Wagner, it's not as bad as it sounds. I suppose it's the equivalent of inevitable wood rot in a wooden hull boat of yesterday.

Home Cookin' you must have really read this quickly... from the 4th paragraph (ie the very beginining of the article) "Osmotic fiberglass blistering is a process which depends on the temperature of, and exposure time to, the water. Given the above mentioned factors, it is not surprising that fiberglass blisters appear on a large number of vessels which are kept afloat for long periods of time in relatively warm water."

As a rule of thumb, degradation of anything is a function of temperature. Steel will oxidize quicker, ploymers will either oxidize or experience hydrolysis
at elevated temperatures. If you've never had to deal with blisters, you are lucky. Nothing worse than finding "chicken pox" on your hull. A long period of time, in the south for blisters to occur is as short as 1 season ( a couple of months) in the water.

 

[dingbat]

Re: Osmotic Blistering

Warm water isn't the cause of blisters. The warmth only exacerbates an underlying problem.

A Problem With a Solution Despite the numerous studies, research reports and magazine articles on the subject, there is not much concordance on the cause and effect of blistering. Most of the literature seems directed at repair solutions rather than how to prevent blisters from occurring in the first place.

The simple fact is that hull blistering is caused by the use of inferior materials and shoddy layup. As Lee Dana, former head of engineering at Bertram Yachts told the audience at the annual conference of the National Association of Marine Surveyors in 1985, hulls built with high quality resins don't blister. If builders want to build hulls that don't blister, all they have to do is "spend another ten dollars per gallon for resin," he said

This fact is well known, but rarely considered by surveyors or the boating public.

http://www.yachtsurvey.com/moreonblisters.html.htm

Some research into the issue

The most important factor found in this type of test related to the use of fumed silica. Silica is used to thicken resin, somewhat like cornstarch thickens sauces. Fumed silica is added to most production laminating resins so that it won't drain out of glass reinforcements when the boat is being built in the mold.

The fumed silica particle is shaped like a flat potato chip, only much smaller. It has irregular edges and a variable aspect ratio. It's a lot like mica in that it has very low shear strength parallel with its surface. It's a very weak substance to begin with, it tends to flake -- and, as it turns out, it was implicated in many blistering problems we found.

Depending on the training received by the laminator or the techniques used by the builder in producing the first couple of laminated layers behind the gelcoat, fumed silica can be concentrated at different depths in the laminate thickness. This can happen when a laminate layer is rolled out in production. As resin flows up through the reinforcement from a pre-wet surface in the mold, the glass fibers in that layer tend to filter the fumed silica out of the resin. This happens most commonly when the builder is using a thick layer of mat reinforcement (over 1-oz. per square ft. in weight). The result is a fine layer of silica platelets spread over the surface of the reinforcement layer. This usually occurs right up against the backside of the gelcoat or between the first and second plies of mat, and can cause moderate to severe interply adhesion problems. In our testing we found that 31% of all blistering problems were caused by the concentration of silica in either of the first two laminated layers.

http://www.practical-sailor.com/marine/Sailboat-Hull-Blisters.html

 

[lkbum]

Re: Osmotic Blistering

Great Post, I agree "Warm water isn't the cause of blisters. The warmth only exacerbates an underlying problem.", I think that is what I was saying. I had a 1984 Citation (made by Fiberskiff in South Carolina). Bought the boat new, after one season, it had very fine blisters at the waterling around the entire aft section of the hull.. Fiberskiff was actually pretty good in dealing with this, ended up replacing the entire hull (took everything out of the existing boat and put into a new hull). I was told by the factory rep at the time, it was due to 1) Cheap Resins, and 2) emerging EPA regulations which were forcing fiber glass builders to use faster setting resins to reduce Volatile Emissions (the explanation was there was less time for the Gel Coat to Crosslink to the resin in the laminate). I was told by my friends (one with a Sea Ray, and one with a Grady White) to get a "better" boat. I kept my boat on a lift ever since. Anyway as for the "better boat" theory, the Sea Ray had blisters on the chines after two seasons (I was told this area is the hardest to get a great gelcoat/laminate bond because of geometry) and the next season the Grady started to get LARGE blisters, which I assumed was due to Hydrolysis of either the gelcoat or the resin in the laminate. I have followed, out of curiousity, blister stuff for a few years and have not seen this Silica explanation. However, if 31% of the blisters in the reference above were due to Silica, what caused the other 69%?

 

[Home Cookin']

Re: Osmotic Blistering

that's interesting about the change in process in 1984. Not that every manufacturer builds boats the same, but it would be interesting to know if there are particularly bad years for hulls, such as the first year a new regulation was in effect and before the builders knew the new process's bugs.

 

[lkbum]

Re: Osmotic Blistering

that's interesting about the change in process in 1984. Not that every manufacturer builds boats the same, but it would be interesting to know if there are particularly bad years for hulls, such as the first year a new regulation was in effect and before the builders knew the new process's bugs.

I was told, by "experts" to avoid any boats made in the early to late 80's. Not sure if this is correct, but prior to this time the only blisters people heard about were from boats that were in the water for several years. I think in the early 90's builders were advertising barrier coats to prevent blisters and Cobalt made it point to advertise that they were the only builder who actually gave a warranty for blistering (I think this is still the case).
PS - Sorry I flamed you in previous posts.... Not the brightest thing to do...

 

[Home Cookin']

Re: Osmotic Blistering

no problem

 

[Tim Wagner]

Re: Osmotic Blistering

The title of this thread sounds like something you would need a giant shot of penicillin to cure.
Good read.
This whole site has made me so smart!! (knowledgeable)

 

[shrew]

Re: Osmotic Blistering

The title of this thread sounds like something you would need a giant shot of penicillin to cure.

LOL. "Dr. my through-hull fitting burns when I bilge water"

 

[Ike-110722]

Re: Osmotic Blistering

Problem With a Solution Despite the numerous studies, research reports and magazine articles on the subject, there is not much concordance on the cause and effect of blistering. Most of the literature seems directed at repair solutions rather than how to prevent blisters from occurring in the first place.

The simple fact is that hull blistering is caused by the use of inferior materials and shoddy layup. As Lee Dana, former head of engineering at Bertram Yachts told the audience at the annual conference of the National Association of Marine Surveyors in 1985, hulls built with high quality resins don't blister. If builders want to build hulls that don't blister, all they have to do is "spend another ten dollars per gallon for resin," he said

Au contrair:

There has been a ton of research by Rhode Island University, funded by the USCG, starting back in the mid 80's as to the cause and how to prevent osmotic blistering. Unfortunately it hasn't made it's way to the public. it's mostly been read by manufacturers and repairers.

Sorry i had to delete the link. I thought there were text versions available on line but they are actually pdfs you have to purchase. I will look for other links.

Here is part of a post I made on another forum:

The study referred to was actually done by the University of Rhode Island paid for by the US Coast Guard Office of Boating Safety. I worked in the Office of Boating Safety at the time although I was not the project officer on this particular project.

A copy of the complete study can be purchased from the Defense Technical Information Center (I tried to post the link but I don't have enough posts according to the error message I got. But if I get an -email or pm I cna give it to you)

The cause is known. What the real question is, What is the cure? Numerous yards, repairers and marine centers have become supposed experts on curing this problem. FRP is a semipermeable membrane, so you simply have to find some way to prevent it from acting as a semipermeable membrane.

The generally accepted method is:
Take the boat out and let the laminate dry. (this can take a long time)
Completely strip off the gel coat and as many layers of glass as necessary
(this depends on the extent of and depth of the blistering because contrary to their popular name "gelcoat blisters" they do not occur in the gelcoat, they occur in the laminate and can be just the top layers, or go clear through the laminate. Some are a total loss.)
Replace the laminate
Replace gelcoat or not (some do some don't)
Apply Barrier Coat (typically some sort of expoxy barrier coat but this varies depending on who's doing the repair.)