Paint peeled off hull

Discussion in 'Materials' started by creativers, Oct 4, 2013.

  1. creativers
    Joined: Oct 2013
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    creativers New Member

    I would appreciate any suggestions as to why my paint peeled off the bottom of my boat.

    My story: Four years ago I bought a 1970 16' Sleekcraft (low-profile ski boat). It had been painted black. I'm pretty sure I sanded the entire boat down to the original green gelcoat. I sprayed primer (I don't recall what kind now). I even used a wax remover/cleaner. Then I sprayed the entire boat with a base-coat/clear-coat polyurethane, with a lot of metal flake in the base-coat.
    I acknowledge that my compressor was way too small, and so I both sprayed a lot with too little pressure, and had to wait around a lot for it to re-pressurize. I blame this for the fact that I couldn't get a very good all over wet shiny finish, even with the clear.
    Anyway, we only take the boat out to fresh water lakes, maybe half a dozen times per summer, for day trips only. But by the end of the first summer, I noticed that paint was peeling off the bottom of the boat, leaving just the primer.
    Given the above, I am mustering up the ambition to strip the entire boat down and paint it again. But I would sure appreciate some advice so it doesn't peel again.
    Do you suppose it has anything to do with the heavy metal flake in the base-coat? I have been reading that it is better to lay a straight base-coat and only use metal flake in the clear coat. But I don't even care about metal flake on the bottom.
    Or could it be because of my periodic low air pressure? (I have access to a 210 volt compressor now. Although I don't know the CFM on it.)
    Or could the type of primer matter? I was under the impression that that shouldn't matter.
    I appreciate your suggestions.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Maybe the primer and the finish coat were not compatible ? Most manufacturers are at pains to point out that you should follow a "paint system", not mix them, which makes sense unless you specifically know there is no problem. Of course that suits their desire to sell you more paint, but in some cases you have to strictly adhere to the stipulated coatings for reliable results.
     
  3. Herman
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    Herman Senior Member

    I never had good luck with PU paints on Bottoms.

    I would plan for a bottom coating of some sort. Tape up the waterline, sand back to gelcoat again, and roll with an epoxy based coating or a hard anti-foul. (do not bother with anti foul if you do not keep the boat in the water for more than 2 consequetive weeks)
     
  4. PAR
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    PAR Yacht Designer/Builder

    Obviously prep is in question. How fine a grit of paper did you use between primer and base coat? What where the brands of primer and base coat? Heavy flake is best over a solid base or in the clear or both. Flake can screw with the bond if they're fairly big and you used a bunch. Does it look like a 1960's dune buggy? If so, and the flake is directly on the primer, yep, you probably know what the next steps are.
     
  5. michael pierzga
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    michael pierzga Senior Member

    As Herman says...Dont use topcoat paint below the water line . Ive seen it bubble off well prepared boot stripes that are submerged.

    For general painting, the two component primer needs a good sanding with fine paper before topcoating . once sanded the surface should be carefully washed with a fine bristle yacht type scrub brush, soap and lots of water to remove dust and contaminanates.
    Contaminantes and dust are the typical cause of poor bonding to a well sanded surface.

    I dont like clear coat...avoid if possible. I have no experience with flake paint
     
  6. mastcolin
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    mastcolin Senior Member

    the single reason for the failure doesn't exist. You unfortunately have multiple reasons it failed.

    1) your compressor is too small. A single phase ie 210(?) volt is never big enough. This will mean you will spray "wet" ie too much solvent will be applied to surface which will get trapped in film.
    2) don't mix primers and topcoat systems. No-one will guarantee work. Some primers and topcoats are incompatible for variety of reasons
    3) you can sometimes use topcoat PU immersed. Some systems don't like it at all. Auto systems are least likely to survive (by and large they skimp on curing agent) it even for short immersion times. Yacht systems increase your chances In combination with 1) and 2) above you are asking for trouble.
    4) what colour did you paint? dark colours are worst for problems. It gets hot and the heat finds the weak link eg adhesion loss due to film expansion and shrinkage due to heat...and the trapped solvent wants to get out blowing the scheme off perhaps?
    5) sorry for asking but did you follow the instructions for application of basecoat and clear with regards to overcoat times, drying temps and humidity, thicknesses, thinners etc? The instructions are very specific for a reason. Working outside suggested parameters increases risk of failure.
    6) did you add a small amount of curing agent to the metallic basecoat? this will increase water resistance and increase your adhesion if you are crazy enough to repeat idea.
    7) the basecoat metallic was metallic out the can or did you add your own metal flake? (don't. It ruins almost every basecoat. Buy the colour with flake added by supplier)

    Cut your losses. Sand the underwater area, Paint it with a black underwater primer. International used to do one (VC Tar2 I think it was called). Or some other epoxy matt black. This will be hard enough for trailer and matt black looks cool against the topside area.

    ps pray the topside paint doesn't fall off.
     
  7. PAR
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    PAR Yacht Designer/Builder

    I agree with most of Colin's post, though with some research, you can mix and match primers and top coats with great success. I also don't agree that adding flake isn't good idea. It's done all the time, I've done it and not had any issues, though I'd never use it straight over primer, as I mentioned only over a solid base coat, likely two. I also don't think an underwater primer is necessary on 16' trailer borne boat with occasional short term immersion.

    The problem we have is we don't know what products he used. Was it a two part polyurethane, for example. I suspect, as Colin does it's a spiraling combination of things, all conspiring to screw with this paint job.
     
  8. creativers
    Joined: Oct 2013
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    creativers New Member

    Thanks to all of you for your comments. I have had a busy weekend, heading back into a busy work week, so I haven't had a chance to pull out the cans that I actually used to give you more specifics. But I can tell you it was a 2 part (that means you add hardener, doesn't it?) It was premixed metallic, with extra metallic, intended for autos. And I sprayed that directly onto the unknown primer.
    So yes, it was probably a combination of several factors. Although I tried to follow instructions, being a novice, I probably improvised where I wasn't sure. There seems to be more info available than I found 4 years ago. So if I take this on again myself, I will be more thorough from start to finish. Thanks again.
     
  9. ondarvr
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    ondarvr Senior Member

    At what level (bond line) did it start peeling at? This will tell you great deal about why it failed.
     
  10. creativers
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    creativers New Member

    Did I forget to clarify that? The paint peeled away from the primer. The primer still holds firm.
    It is clearly from the pounding of the water that the underside has peeled off. But also on the top side and sides, wherever I've bumped up against docks, etc., it has tended to peel or scratch back to the primer.
    So, my hope is to sand the entire boat back to the gelcoat and start over, over the winter.
     
  11. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    If you have a good primer bond, why sand it off? Most primers are compatible with most top coats, it's the nature of the beast. You top coat prep or the top coat itself are the issue.

    It could be as simple as too fine a grit, prepping for the top coat. There has to be enough "tooth" for the top coat to grip. Too fine a grit will prevent this. You could have left a residue when you cleaned the primer, before the top coat. It could be an compatibility with the primer - was the primer an automotive version, like the top coat? Lots of things it could have been. You can start from scratch, using compatible products, which would be the safest bet, or knock of the top coat and do some test patches to see what works, which would be the cheapest.
     
  12. mastcolin
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    mastcolin Senior Member

    The point about mixing and matching primers and topcoats "with some research" means basically trial and error. Sticking with one supplier means someone else did the trialling so you don't get the errors.

    The cost of any job is way more in labour than material. Think 70/30 or there about. If you go experimenting and it goes wrong you lose big. if your experiment is successful your gain is minimal. So where is the benefit?

    It is purely a commercial/game theory decision. Obviously there should be no risk in using some primers and some topcoats. But when it goes wrong you end up paying the bill.

    The history of the world is littered with failures caused by people assuming that the unproven is acceptable risk.

    I agree, he doesn't need paint on the bottom, but I presumed he wanted to cover up the sand original green gel/primer. Also if the gelcoat is exposed whilst sanded and left it will get very dirty and you won't keep it at all clean. Paint it with something tough and black. Forget about ever even cleaning it again:)

    Best of luck next time.
     

  13. jimmy wise
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    jimmy wise Junior Member

    ok i can chime in on this, 32 years painting auto and truck. the reason its delaming from the primer is your primer choice needs a sealer coat for impact resistance. thats why its coming off so easy. im guessing you used an economy primer. there is no chemical bond between the base coat and the primer and the mechanical bond isnt there. that is why you need to use a system. always ask for a product data sheet. clear coat is not good in the water. mold can grow under it if the boat stays in the water. paint is expensive you get what you pay for
     
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