Fiberglass and Gel-Coat Repair

K

ken emigh

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Need some direction. First, have two small cracks in hull, below water line, what product should I use? Both about 8-inches long less than a 1/8 of an inch wide. Secondly, have wear spot side of hull, size of golf ball, through gel coat. Did not go through fiberglass but down to it. Again what should I use? Doing repairs myself.

Thanks in advance!
 
Marinetex below the waterline and the other repair sounds like a gelcoat repair.
 
If its not thru the fiberglass, do a gelcoat repair with matching gelcoat. Below water line, prep and repaint with bottom paint after the repair. The repair is really no different above or below the waterline. Remember, your boat has the same gelcoat everywhere. Gregory, sorry, but I disagree with you on the marinetex...that's an epoxy adhesive and it will bond well to the polyester gelcoat, but if a future repair is needed in the same area, polyester gelcoat will not bond to the epoxy. Also, adhesives are not gelcoats...they have 2 different functions. just my 2 cents.
 
THe bottom is painted so no reason to gelcoat over the repair. No need for gelcoat here. I'd use marinetex and then repaint. I think most yards would do it that way also. Different matter above the waterline where he needs a gelcoat repair. Why would you go thru all that trouble of a matching gel repair if you were going to paint over it???
 
The issue isn't the look its the prevention of water penetrating the glass and causing more work down the line,use West System below the waterline,sand down to match existing surfaces,repaint.
 
Exactly. I like Marinetex or 3M Marine fairing compound as to me it's easier to work with than the West System. That boat ( a 32 Carver) is never going to be without bottom paint, so no need to match the gelcoat below the waterline. These repairs will also be stronger than the original gelcoat.
 
Let's say instead of a small crack, he had a significant damage to the hull below the water line and it needed to be professionally repaired. After the fiberglass guy repaired the damage with new fibeglass, do you think he'd marinetex or west system in lieu of gelcoat or he'd spray new gelcoat to match the old to make an invisible professional repair? If gelcoat works for a large damage,why not for a small crack?
 
The repair actually depends on the type of bottom paint. If you use a hard epoxy paint then the repair will be protected by it. However if the bottom paint will allow water to permeate through it then you should re-gel coat the crack using the same polymer as the gel coat. The reason is that epoxy does not bond well to gel coat as stated above. Thus water will penetrate the bond line between the epoxy repair and the original gel coat. The water then can permeate the fiberglass resin and compromise the hull structure.
 
He's not going to put Marinetex or west on gel coat, he's putting it on and into the laminate. So let me get this straight, you're going to re gel below the waterline and then sand it to accept barrier coat and bottom paint? By the way, gel coat isn't impermeable to water, but Marinetex and the West system are. I don't believe any "yard" would do it that way. Just curious, but have you ever fixed a gouge below the waterline on a painted bottom????
 
Actually current vinyl ester Gel coats are nearly impermeable to water, and while you are correct in the original polyester gelcoats do allow water permeation they do so by inter-molecular diffusion. The bond line permeation is a much more efficient mechanism of water transfer (due to the relatively large molecular spacing along the bond line caused by physical rather than chemical adhesion) than the diffusion through polyester gel coat. Since he is not removing all of the gel coat from the entire underwater portion of the vessel there will be an underwater bond line between the gel coat and epoxy. If you were to read my comments carefully you would note that I did not comment to diffusion through the epoxy per se but through the bond line.
To satisfy your curiousity I have worked on vessels for over 30 years, and am a consultant to numerous companies including those in the marine industry on surfaces and interfacial bonds in hostile environments such as the marine environment.
You are correct in your inference that many marine yards do not repair underwater defects correctly. The numerous comments testifying to shoddy workmanship contained within this Forum servesas ample testimony.
 
OK, pardon my ignorance here I'm no expert but, isn't West System an epoxy? And ins't Marinetex an epoxy? Gelcoat on an older boat will likely be polyester. So If a repair is done with West vs Marinetex isn't about the only difference one of final color and finish? Asthetics aside, I tend to think that an epoxy repair (whatever brand) will provide a more water proof job than polyester gel coat.
Back to your bond line statement, will there not be a bond line regardless of the repair material used? If so, won't there be a likelyhood of permeation from the same characteristics stated in your previous message? Or are you saying that repairing like with like will reduce the size of the molecular spacing along the joint thereby reducing the permeability at the joint?
Not trying to be arugmentative here, only trying to understand this topic better.
 
Mike, I would apply barrier coat over the repair before applying any anti-fouling paint. Therefore, it wouldn't be a "shoddy "repair . This is an older Carver he's talking about, long before vinyl ester gel was used. So if you repair with the original gel, it would be polyester.
 
Scorpio--I perhaps wasn't clear. The bond line between polyester and epoxy is a physical bond, that is, the bond is formed by the two surface mechanically interlocking somewhat like a jigsaw puzzle. The bond line between a (properly prepared)existing polyester and another fresh polyester will be both chemical and physical, that is the roughened surface of the old polyester will contain a few chemical sites through which a chemical bond may be formed. Water diffusion along the chemical bond line is drastically reduced compared to the physical bond line. ALso the chemical bonds are not broken by the water diffusion while the moisture in a physical bond line act as a lubricant and will slowly diminish the bond integrity.

Greg--You are absolutely correct--If a subsequent barrier coat is applied then the moisture can only reach the bond line via the minimal diffusion through the barrier coat. In that case your procedure is absolutely proper.
 
Mike, isn't the chemical bond also increased if you apply some styrene to the existing roughened gelcoat before applying the new gelcoat?
 
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