Refinishing - Hairline Cracks

Discussion in 'Boatbuilding' started by savagescout, Jan 6, 2015.

  1. savagescout
    Joined: Jun 2009
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    savagescout Junior Member

    Hi All,

    I am now at the stage of my project where i am going to repaint my hull. The hull has original gelcoat (circa 70's era) and i intend to dewax the hull, followed by sanding back with 80-120grit (filling as required) prior to priming with International brand Interprotect.

    Obviously major scratches and holes will be filled but i have plenty of hairline cracks in the deck/cap of the hull as shown in the photos below.

    [​IMG][/URL][/IMG]


    [​IMG]

    What is the best way of treating these? Really appreciate any advice that can be offered.

    Thanks All.

    Nick.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Looking at all that crazing, you may go craze-zee getting a good finish. I'd say a sandable undercoat with good filling properties, as part of the paint system, would be the order of the day, might even be best brushed in.
     
  3. ondarvr
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    ondarvr Senior Member

    That gel coat looks like it was applied incorrectly when the boat was built, so it's basically trash stuck to the outside of the boat. Crazing like that is normally from being over or under catalyzed, and possibly a little thinning with acetone thrown in to help it fail.

    You have a couple of problems trying to cover it.

    As the cracks increase and decrease in size due to temperature, stress, etc. whatever you put over it tends to crack also. Some times right away, sometimes a little while later, but the chances of it failing again are very good.

    Second, the gel coat is very weak due to whatever they did to it during application, probably thick too. So it makes a terrible base for anything to go over it, chunks could start falling out from the new stresses from a top coat.

    The correct fix is to remove all the crazed gel coat down to the glass and rebuild the surface.
     
  4. dinoa
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    dinoa Senior Member

    I second ondarvr. That gelcoat is gone. It is a bad foundation to put anything on. It also exposes the underlying laminate to water and aerosols which slowly take their toll. Is the underwater gelcoat and bootop also effected?

    Dino
     
  5. savagescout
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    savagescout Junior Member

    Thanks guys, not the answers i was hoping for but i guess deep down i had them already.

    Luckily the crazing is only limited to the top deck and is not existent on the hull sides or beneath the water line. don't get me wrong, there is a couple of spider cracks here and there but nothing like the consistent hairline cracking shown in my other photos.

    Once i have removed the gelcoat (presume by dual action sander?), how would one typically go about repairing these areas?
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    We are likely talking about a boat several decades old that has seen much sun exposure. To hell with sanding off the gelcoat, that is just making a mountain of work that is easy to counsel someone else to do, but realistically paint can hide a multitude of sins, and that is the way to go, imo. Whatever is going to crack, has already cracked. In any case, it is not structurally vital, more cosmetic. Paint and forget ! ( Except maybe remember to keep the boat undercover more)
     
  7. ondarvr
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    ondarvr Senior Member

    While age is part of the issue, the gel coat was not applied correctly, old gel coat does not craze like that unless there are more underlying issues. Painting over crazed gel coat leads to crazing in the paint. Why even go through the hassle of painting if there's a good chance it's going to look like crap again soon
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    You will have a freshly crazed finish, rather than the "antique" crazed finish, if the worst happens! I doubt there is a solution that makes any sense to get involved in, the gel coat may have been too thick and the underlying laminate too thin, and hot sun and flexing etc did the rest. Sanding it off, and then re-finishing, is going to be a nightmare. I'd rather paint it with a flexible topcoat, even acrylic house paint, that will look much better than the current eyesore, and likely won't crack. Life is way too short to invest countless hours in doing it the "purist" way. And you'll never get paid come time to sell.
     
  9. Jim Caldwell
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    Jim Caldwell Senior Member

    How about scuffing the gelcoat with a sander then sealing with a coat of epoxy then paint?
     
  10. tom28571
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    tom28571 Senior Member

    People who have attempted to paint over such cracks are the ones you should listen to. No thin coating ever succeeds in permanently covering such cracks. Extremely difficult to get any coating to actually penetrate the cracks and the cracked gelcoat will continue its devilish work. Thin coatings like paint hate sharp edges and will pull back from the edge and not enter the cracks because of surface tension, or more accurately surface free energy. Removing all the gelcoat is a considerable job and you still have to recover with something.

    Sand the gelcoat fair with an aggressive sander. Vacuum the dust out and squeegee on thickened epoxy which will at least partially fill the cracks as you force it in. Then sheath with 6oz fiberglass and then paint. This works well as many who have covered checked fir ply decks can attest.
     
  11. ondarvr
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    ondarvr Senior Member

    Sometimes a coating of just epoxy works, sometimes it doesn't, it depends on how bad the crazing is and cause of it.

    In his first post he asked "what is the best way of treating these".

    The best way is to remove them, once that's been done the problem is gone with no chance of it returning, other methods leave the possibility (some guaranteed) of them returning.

    Crazing means the gel coat didn't crosslink correctly and the physical properties are low, that's why it cracks in the way it does. It also normally means it's too thick, thinner sections tend not to craze as often even if they have the same under cured issue because the stresses are lower in a thinner film.

    If the affected area is huge, and I've seen entire decks on larger boats crazed, then the idea of removing all the gel coat and re fairing the surface can be cost and time prohibitive, but on smaller areas when it appears only certain portions are crazing, it's not that difficult to grind it down and build it back up. If I'm going to go to through the time and expense of painting a boat I don't want defects in the surface showing up on day one, or 2 years down the road.

    The sheathing method works well, it gives a new solid surface to work with. Sometimes I've found the gel coat to be up to 3/8 of an inch thick and it often requires glassing (with epoxy or polyester) to get it right again.

    The repair method chosen is totally up to the owner, he can decide how much time and money he wants to invest in this project, and he is the only one that needs to be satisfied with the end result.
     
    Last edited: Jan 8, 2015
  12. pescaloco
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    pescaloco Senior Member

    You should look into having the deck Soda blasted to remove all of the old gelcoat
    I think you would be wasting your time to overcoat with out removing the crazing
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Any paint that acquires a degree of hardness will likely crack, hence my "bodgie" suggestion to use an acrylic house paint. Sure, light colours would just get too dirty, but I'd rather have that finish than the current look.
     

  14. gtcway
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    gtcway Junior Member

    Is that a Boston Whaler? I've seen lots of early 80's and older Whalers that have been in the sun most of their lives that look exactly like that. Some worse, some not so bad, but it seems like every one that has been in the sun most of it's life is like that.
     
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