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Thread: How do I Paint A GRP Hull

  1. #1
    Join Date
    Jun 2009
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    Preston, Lacashire. (Unlike Bolton..........lmao)
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    Default How do I Paint A GRP Hull

    Hello to all you paddlers.

    I have recently bought a couple of cheap and tatty looking kayaks. One is worse than the other.

    Kayak 1.

    The bow & stern have been slightly damaged and a poor repair has been done to these areas. The hull and topside are in good condition without any damage but the gelcoat is looking scratched and worse for wear. The seam along both sides is looking a little suspect.
    My intention is to rub down the entire structure and and to scrape out (not to seperate) and re-seal the seams with 2 pack resin. (Stop me if you think this is a bad idea)
    My main issues are with what paint systems would be best for both durabilty and looks.
    I have searched the net and information seems sketchy to say the least. I have looked at some posts here and have found some helpful hints but nothing too comprhensive.
    I think I will be going down the 2 pack route, but I'm unsure of which product to buy and where to buy it from.

    Kayak 2
    This one is generally in good condition without any damage. The Gelcoat on the hull has a few hairline cracks but they are only to the gelcoat and not the GRP. I am a little worried that if left these will allow water to penetrate and cause further damage. My intention is to rub down the hull and recoat using a 2 pack system. (Same problems as above) What to use and where to get it from.

    For both kayaks I would like to fit a durable PVC/Nylon type rubbing strip to cover the seams and give a little protection. Are items like this availble and if so where could I get hold of some?
    Regarding the fixing of this, would I glue and rivet this or would there be a different method?

    Many thanks to you all for taking the time to help out and pass on your hard earned knowledge.
    I'm looking forward to getting out on the water soon. I have never had a single cockpit kayak before so it's going to be a learning curve. I might just tow my coleman along behind just in case I need to bale out........lol

  2. #2
    Join Date
    Jul 2007
    Location
    Robin Hood's Bay,Yorkshire
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    2,067

    Default

    I'd go to a boat yard, or if there is none around you then try a good car respray shop. This is bread and butter to both of them. They'll gladly help you.
    http://www.davidwperry.blogspot.com/

  3. #3
    Join Date
    Feb 2008
    Location
    Kenilworth
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    72

    Default

    The seams are normally done with fibreglass tape and then covered in gel coat. The hull should be similar with a thin layer of gel coat covering fibreglass. You can certainly colour gel coat so if you want to paint the hull that would work and stick properly. The problem with paint is that it flakes off, I painted a kayak deck with car paint and it didn't stick well. If gel coat is too expensive I would try car bumper paint, it's intended to paint plastic rather than metal so it sticks better and stays flexible. If you need to find a local supplier look through this web site http://westsystem.com/ss/
    Last edited by JS1; 30th-March-2010 at 09:05 PM. Reason: Link added

  4. #4
    Join Date
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    Default

    You´re facing one of the big problems in the fiberglass world. Most of the grp products that you probably know are made with an external coat of gelcoat. Gelcoat is a coloured resin (usually polyester with pigments and other aditives), sprayed over the mold. When partly cured, fiberglass with resin is aplyed over this gelcoat layer, creating a very strong bond. As you can see, grp products are usually made from the outside to the inside.

    Gelcoat, as a plastic, suffers a lot with UV. Also, it usually does NOT follow the bending properties of the structural layer with fiberglass beneath, generating small cracks on the surface when submited to bigger stress. Don´t worry about these cracks on your small boats that don´t stay year after year IN the water. The structural layer (grp) beneath will outlive your grandchildren in this case. Gealcoat small cracks are a concern just in big boats that are always in contact with water.


    One of the main advantages of using a gelcoat is that the colour is literally part of the laminate, not just a thin skin over it (as a painted surface). One of the main disadvantages is that the gelcoat does not take very well any kind of repaint after. Their formulations are exactly to be as closed as possible, and many aditives as neo-pentil-glycol are added to close the molecular structure as much as possible.

    In the GRP car/truck industry the process is quite different, as painting is the final coat. They apply a different kind of gelcoat, that works as a primer (in true, it´s called primer gelcoat!!! ) And, as you can imagine, this primer gelcoat is based on polyester resin plus aditives to open the surface structure, such as minerals and glass micro spheres. The cure is a bit different too, leaving a porous surface that will anchor the paint quite well.

    OK, so what can you do? Sanding the original gealcoat is the most basic way of opening it´s surface to a better bonding of the next coat. Something as coarse as 180 grit! Wash the sanded hull with water and neutral detergent. Do NOT use any chemical to wash the surface, as this will melt the plastic surface and close the pores again (many people don´t understand this and waste time and money by loosing the initial sanding! Quite stupid, I know...) . Dry the surface with compressed air or leave for two or three days in a dry shaded area. I do NOT recomend trying to paint with gelcoat. This is a very difficult job and gelcoat is usually 100 times mores viscous than paint! Thinning gelcoat is a risk bussiness. And the curing process will change dramatically. Small gelcoat reapirs are ok, but painting an entire hull is completely different (not to say impossible in a homemade basis).

    Go for an automotive "nitro-laca" (paint) over an automotive (nitro-laca) primer aplied over the sanded dry hull. The primer coat is essential, as it is THE bonding layer between gelcoat and paint. Some people skip this step and complain later about the paint stripping in large pieces from the hull. You may end up your beatifull job with an automotive transparent varnish (may be epoxy or laca!).

    Now just remember that all you have is a micrometric layer of paint there, so scratches will happen and may reach the gelcoat layer again.... Just like in your car! BTW, what gives real resistance to your car paint is the varnish, not the paint..... More expensive models always have a varnish coat over the paint. Average models may have it or not.... Cheaper model almost never have...

    well....what else? What were we talking about?
    Tony BR
    www.companhiadecanoagem.com.br
    www.canoacanadense.com.br/english.htm
    Past 20 years teaching Biology!
    Next 20 building Canoes!!!

  5. #5
    Join Date
    Aug 2009
    Location
    Portsmouth
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    241

    Default Paint grp hull

    Epifanes two part paint was the paint of choice for the boat repair company I used to work for. A first class product for painting G R P. All the info you require below.

    http://www.epifanes.com/home.htm

  6. #6
    Join Date
    Jun 2009
    Location
    Preston, Lacashire. (Unlike Bolton..........lmao)
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    54

    Lightbulb Thanks people

    Thanks for the replies guys and/or girls.

    I have been ispired by some work Pete Thomson has done on his canoe. His entry is here.

    http://www.songofthepaddle.co.uk/for...ng+fibre+glass

    I have decided to go down his root of sanding, washing, sanding, sanding. I am going to polish then wax after I have done all the necessary repairs.

    Many Thanks to Tony for his help too. A very well informed and helpful guy.
    I will probably be doing a piece on it on here as I have already begun this weekend.

    Cheers all

  7. #7
    Join Date
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    Good sanding DogBoy.....

    Some people say that boatbuilding is "just" about 90% sanding! By experience I would say that boat repairing is "just" about 99.9% sanding!!!!

    If you´re going this way, sanding from 360 up to 600 or even 1200 grit may be necessary, than polishing through 3 grades of paste for a final waxing. Just remember that the gealcoat layer on small boats is just 1/2 milimeter thick (some old fiberglass boats used to have 1 to 2mm thick layers) .

    Waiting for the pictures!
    Tony BR
    www.companhiadecanoagem.com.br
    www.canoacanadense.com.br/english.htm
    Past 20 years teaching Biology!
    Next 20 building Canoes!!!

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