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11 Year Slow Motion Wreck Of A Paint Failure.

Discussion in 'Ask All Sailors' started by rardiH36, Aug 7, 2018. Add this thread to a FAQ

  1. rardiH36


    Joined Jun 21, 2007
    2,082 posts, 50 likes
    Hunter Cherubini 36_80-82
    US San Francisco Bay's "Hurricane Glitch"
    Bear with me as I describe the time-line of my 11 year slow motion paint failure which I feel was caused by UV penetration/degradation of the epoxy primer underneath:

    - Bought my 1980 boat. (27 years ex-yard then. 38 years old now.)
    - The white gelcoat on the cabin top was total chalk. A rub down with just a dry terry cloth towel in some areas revealed the underlying layer of actual fiberglass mat layup.
    - Power sanded all down to a firm paintable surface.
    - My choice was to renew the surface with a major manufacture's marine 2-part polyurethane. (Will not divulge the manufacturer here.)
    - Followed instructions exactly.
    - First step was to apply a 2-part epoxy primer coat. (But I do recall debating whether this was necessary or if I should simply apply the finish coat.) Even though I followed exactly the instructions as to the ratio of the manufacturer's $25 a pint thinner, and I applied in cool weather, brush marks did not "wet" out. The epoxy primer set rock hard. So lots of sanding to rectify. Eventually good to go. The hardened primer was almost pure white.
    - Then applied two coats of the 2-part polyurethane. One of the manufacture's "white" colors. Also mixed in some flattening agent since I didn't want super high gloss. Did not exceed the max allowed ratio of paint to flattening agent.
    - Job not perfect but still I was quite pleased with the result. And several years on, the surface of the 2-part polyurethane had not degraded at all. Just as advertised!


    - I started to notice that in certain areas of my paint job, the color was turning from white to a sort of tan. Chipping away a bit at those locations, the 2-part surface paint separated easily from the underlying epoxy primer. The surface paint chips were still white. But the underlying primer no longer was.
    - Trying to analyze, I recalled reading that epoxy degrades with UV exposure. Maybe two coats of white 2-part polyurethane mixed with the flattening agent wasn't enough to block UV penetration onto the epoxy primer? And the primer itself was degrading as a result?
    - I called the manufacturer for advice. Just got a vague "strange" and "don't know" type of response.


    - Even though the 2-part polyurethane surface was still looking much like the day I applied it, I decided to put another couple of coats to thicken the layer and hopefully prevent further UV penetration to the underlying primer.
    - I didn't machine grind/sand everything down to virgin FRP. But over a couple of weeks, hand-sanded the hell out of the surface. Again followed the manufacturer's recommendations as to surface prep and application. Since the surface was now smooth and solid, I did not need to pre-coat with primer again.
    - All looked good. Again, the 2-part paint surface does hold up splendidly over the years.


    - Every so often and in just a few small sections, the 2-part polyurethane would simply peel away from the now tan epoxy primer. Particularly if lightly impacted with something dropped.


    - Had been since 2013 that I painted my port surrounds. Were looking a bit tired.
    - On a recent the afternoon, applied blue 3-M masking tape over the cabin top 2-part polyurethane.
    - Painted the surrounds the next morning.
    - Removed the masking tape right after.
    - Look at the attached photo! The 2-part has almost totally separated from the underlying primer!
    The once white epoxy primer is totally yellow/tan. And I can even put a gouge in it with a fingernail. No longer rock hard!

    My solution going forward: Old boat. Plus less finicky and getting older owner. Don't want to deal with grinding/sanding down the surface to remove everything. (Which in California anyway shouldn't be done at the berth due to water contamination concerns.) I will simply whimp-out and dab on white 1-part polyurethane wherever paint separation happens.

    The other photo is the appearance of my deck and cabin top during happier days gone by.

    Anyone else have UV failure stories?

    Attached Files:

  2. MitchM


    Joined Jan 20, 2005
    706 posts, 98 likes
    Nauticat 321 pilothouse 32
    US Erie PA
    it's disappointing that the 'tech service' people at the anonymous paint manufacturer were so unhelpful. can you post who they are ?

  3. Jackdaw


    Joined Nov 8, 2010
    9,656 posts, 2,709 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    That’s really too bad, because that’s a real nice looking 38 year old boat!

    And an interesting problem with a potential cause I’ve never thought of before.

    Last edited: Aug 8, 2018
  4. Sumner


    Joined Jan 31, 2009
    5,172 posts, 217 likes
    Macgregor 26S/Endeavour 37 .
    US Utah's Canyon Country
    Normally there is a time window between epoxy primers and top coating them (24-48 Hours?). This is so there is a chemical bond between the epoxy and the top coat. Sounds like you went past that but recovered by sanding the epoxy to create a mechanical bond between the epoxy and top coat. With the epoxy products I've used if you go past the window they want you to sand and also apply one more epoxy coat before going on, again within the appropriate window.

    Not sure what happened in your case but obviously you didn't get the bond between the two that you needed. Good luck and I hate painting since there are a ton of things that can go wrong,

    1300 miles to The Bahamas and Back in the Mac...
    Endeavour 37 Mods...
    MacGregor 26-S Mods...
    Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

  5. ggrizzard


    Joined May 27, 2004
    1,053 posts, 108 likes
    Hunter 30_74-83
    US Ponce Inlet FL
    I'm no expert but...
    The area around your port lights that seems to have 'failed' is the area where
    excess silicone sealant residue may have been left behind after a refit.
    Just my SWAG.

  6. rardiH36


    Joined Jun 21, 2007
    2,082 posts, 50 likes
    Hunter Cherubini 36_80-82
    US San Francisco Bay's "Hurricane Glitch"
    Your observation prompted me to have a look again at the instruction sheet from both the 2-part epoxy prime-kote and the 2-part Polyurethane. The prime-kote says minimum 10 hours to cure. Then sand before applying the finish coat. Maximum time for applying the finish coat is simply a "-". Which I still think to mean can be several days if need be. As long as well sanded with 220 grit. Anyway on my boat the 2-part surface paint stayed well adhered for quite a few years. Only began to separate as the underlying epoxy primer began to turn yellow and tan. I have re-painted my port frames several times over the years. Masked each time. Paint never pulled away before. I am still thinking a chemical breakdown of the epoxy prime-kote has happened as the years rolled on.

  7. rardiH36


    Joined Jun 21, 2007
    2,082 posts, 50 likes
    Hunter Cherubini 36_80-82
    US San Francisco Bay's "Hurricane Glitch"
    Wasn't the case on my boat. These are the original ports from 1980. When I did my original prep work, the old gelcoat around the ports "dusted" away easily down the the fiberglass mat layer. I cleaned liberally with solvent before applying the epoxy prime kote. The primer is still attached to its substrate. I have never waxed the cabin top. As I just responded to Sumner, I have painted my port frames several times over the years. This is the first time the masking tape pulled the surface paint away from the primer. Bummer because I am now expecting that over the next few years, the 2-part polyurethane will began to randomly flake off on its own as the primer layer continues to degrade.

  8. agprice22


    Joined Aug 3, 2012
    2,221 posts, 472 likes
    Performance Cruising Telstar 28
    US Watkins Glen
    If the epoxy was allowed to cure, it leaves a blush which requires cleaning and sanding. Awlgrip (sounds like your product) and other 2 parts can be difficult to use. Using reducer makes it like 3 part. The high build and sealer primers as well as the top coat need to be recoated quickly, depending on temperature, within an hour, for optimal adhesion. Left to cure too long, and they will set and blush. To switch to the next product, you must clean and sand and clean to remove chemical residue, smooth the surface, and remove dust prior to the next product. Reducing requires choosing the right speed reducer and the right reduction amount. Further, the reducer evaporates over time, so you have to add reducer as you go. Reduce and test for proper leveling. Watch your brushing. When it stops leveling, add reducer , and reroll / rebrush the recent section. It will rewet and level. Wetsanding and polishing may be necessary in any case. Horizontal sections will be easier and more level. The awlgrip 2000 can be polished. Others may not. Check your product.
    Also, 11 years is not short. That seems like a good lifespan. It is not gel cote.
    I doubt you were too far outside the parameters. Flaking usually indicates a contaminated surface. Did you dewax before sanding? I know it sounds crazy, even grinding down to the fiberglass can leave residue.

  9. rardiH36


    Joined Jun 21, 2007
    2,082 posts, 50 likes
    Hunter Cherubini 36_80-82
    US San Francisco Bay's "Hurricane Glitch"

    You provide a lot of good observations. Should be required reading for anyone embarking on a multi-step painting project!

    Yes, I agree that 11 years on before failure is a pretty good outcome. But I had expected that with time it would be the actual top surface that would begin to fade/oxidize. And it would "simply" be a matter of a good cleaning, sanding, wiping clean with the recommended solvent, and then applying a new surface coat. On my boat, I have never-ever waxed the cabin top. Just for the reason to avoid the risk of wax residue complicating a future paint job. What has happened, as I described, is whilst the epoxy prime-kote still remains firmly adhered to the substrate of the original OEM cabin top, it is the outer surface of the prime-kote that has turned yellow and no longer hard. I can only think that over the years, UV cumulatively has penetrated through the 2-part polyurethane and had degraded the epoxy primer underneath thus destroying the bond between the paint. (Just occured to me that I haven't yet thrown away the masking tape the pulled off the surface paint ... still in my boat's trash bin. I should take a look and observe what color the white 2-part is on the underside. Might offer up another clue. If white, then a clean separation. If yellow, then the paint is still adhered to the prime-kote -- and its the prime kote that has failed.)

    I also used the same 2-part polyurethane for my non-skid ... done about two years after the smooth "white" paint project. The OEM non-skid was still in great structural condition. Just looked old and stained after 27-28 years. It also had never been waxed. For surface prep, I just gave it a good deep cleaning with a strong cleaner. Rinsed well along with lots of scrub brush effort. Then just applied the 2-part with a paint brush -- mixed with non-skid granuals and flattening agent. 8-9 years on, the job looks much the same the day I painted it. Nowhere is it flaking off. Glad that I didn't epoxy prime-kote first! Showing the non-skid, attached is a photo from a few years ago which I took for a post about leaking chain-plate covers. I masked around the non-skid over the now failing 2-part polyurethane surface. Back then, nowhere did the masking tape pull anything away when I removed it.

    Attached Files:

  10. agprice22


    Joined Aug 3, 2012
    2,221 posts, 472 likes
    Performance Cruising Telstar 28
    US Watkins Glen
    How many coats of topcoat did you apply? The topcoat has a minimum required thickness to provide complete protection, and Awlgrip says, depending on application method, that 3-4 coats may be required and should be done no more than 12 hours apart without sanding. I think 45 minutes is the minimum. It is kind of hard to paint a deck without walking on it!
    It honestly sounds like you found the Achilles Heel: the sealing primer was not made UV protected.
    The sad thing is that we eventually come to the day when we will not embark on a major overhaul. I do not know when my last will be, but there have been moments when I have seriously considered taking a reciprocating saw to my boat!

  11. rardiH36


    Joined Jun 21, 2007
    2,082 posts, 50 likes
    Hunter Cherubini 36_80-82
    US San Francisco Bay's "Hurricane Glitch"
    Hello again agprice:

    Thanks your continuing interest in the discussion.

    Initially the cabin top was done with three coatings of 2-part. Then about 4-5 years later, when I first noticed the dis-colorization that seemed to be showing through from underneath, and when I first considered possible UV caused decomposition of the epoxy primer, I added two more coats. At that point I just thought it was a dis-colorization issue. Rather than it escalating into a failure of the bond between the top paint and the primer.

    Today I did check the underside (sticky side) of the masking tape that pulled away the two part top paint from the primer. A couple of pictures attached. Nice and white. Another indication of a primer bond failure.

    Back 11 years ago when I did the original paint project, I also had a few small spots where the gelcoat had chipped away from the underlying FRP due to impact by the PO's. On the transome. And at the bow near the water-line. As an afterthought with only a 1/4" already mixed 2-part at the bottom of my plastic paint "can", I dabbed over the chipped spots with an artist brush. Didn't sand. Didn't solvent wash. No primer. I looked at these areas today. The 2-part is still firmly attached and in fine shape. Another indication that on my cabin top, it is a bond failure between the epoxy primer and the 2-part.

    Yes, I agree with you that at some point, I will not bother with the super-major effort/expense of a significant project on a 40 year old production boat. Plus I am a 66 year old owner who unfortunately probably will begin to lose interest and/or ability within the next 10 years or so anyway. A major cash outlay won't yield anyway near the $'s spent when the boat is sold. So not much point is there? Don't get me wrong. I have always been pleased with my choice of the 1980 Cherubini Hunter 36. If I hailed from the east coast where boats are hauled out every winter, and I also lived close enough to have it transported to my property that might also be large enough not to bother the neighbors, then yes I would undertake the project of grinding/sanding off all of the existing paint and primer. And start anew. But we don't haul out here in California except for the periodic bottom job. And homes are close together. Even with a vacuum sander, noise, dust and paint chips wouldn't be tolerated by neighbors. And would violate city/county ordinances.

    Attached Files:

    Last edited: Aug 10, 2018
  12. agprice22


    Joined Aug 3, 2012
    2,221 posts, 472 likes
    Performance Cruising Telstar 28
    US Watkins Glen
    Interesting situation. I will watch my boat with interest. I used High Build Primer over glass and filler, sealing primer, and Awlgrip 2000, sprayed. I also have brushed Awlgrip 2000; although, awlgrip says it is for spray only. It turned out great.
    The boats I have seen fail have failed in several seasons, not 10 or 11. The failures have been due to moisture and poor surface prep.
    I am on the East coast. We pull our boat yearly, have 6, long, boring months waiting to work on them. We end up rushing our work in April and May. This season, I will finally have my workshop, so I can work indoors!
    Take care.

  13. JetLaggedChef


    Joined Jul 9, 2018
    64 posts, 23 likes
    Catalina 25
    US Lake Monroe
    Hi radiH36. Tomorrow, I am looking at an '81 Hunter Cherubini 36 here in Florida. It seems to be well maintained (and of course I'll be getting a surveyor if I like what I see on my initial walk through.)

    I'm going to surf through all your threads to see what kind of things you've encountered with yours, but since I'm short on time I was hoping you might be able to quickly point out any major issues that you've had with yours. I already know all the standard things to look for, I'm really looking for issues that this particular boat might be known for. (E.G. - the chain plates tend to leak badly, etc.)

    Thanks in advance!

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