Pinholes in the gel coat problem.

Discussion in 'Fiberglass and Composite Boat Building' started by Seb790, Aug 29, 2009.

  1. Seb790
    Joined: Aug 2009
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Europe

    Seb790 New Member

    Hi everybody, it's my first post here. Sorry for my English.

    I'm a regular member of various aviation forums, in the part time I'm into cars, I would also like to have a nice power boat one day too.
    Currently I have a little problem with pinholes in a gel coat. I'm prepering my car for sale pic1 (I need some money for other projects), and I have to make one more part pic2. In the past sometimes I had problems with those pinholes pic5, and I really don't want to have those problems again. So I asked guys at aviation forums but probably they have very little experience with it, because I got very little feedback. So I decided to ask here because you guys deals with gel coat regulary.

    I'll try to describe my technique so it will be easier for you to judge what I'm doing right what wrong.
    The gel coat which I use is already accelerated, so I'm only adding a hardener to it about 1%.
    I'm apllying it with a brush for a few reasons, don't have a proper compressor at the moment, don't have a proper spray gun, and "spraying' black gel coat is unavailable localy unless I buy a small barrel probably 20kg, but I need only about 1.5kg.
    I was using different tools for mixing from wooden strips to steel rods, at the moment I mix it with a electric drill pic3 and a small "tool" (pic4), I believe I have the best results with it.
    I'm also "warming up" gel coat a little bit usually with a warm/hot water pic3.
    After applying a layer of gel coat sometimes I also use a heat gun (I was trying also a hair dryer) I believe it help me to remove "invisible" air bubbles, seems like it works.
    Parts aren't painted (that was probably the bigget mistake) pic6, polished gel coat surface.

    The main question is ,is it anything what I can do with that potentical pinhole problem.

    Seb
     

    Attached Files:

  2. Itchy&Scratchy
    Joined: Jul 2008
    Posts: 140
    Likes: 3, Points: 0, Legacy Rep: 117
    Location: Oxford & South Africa

    Itchy&Scratchy Senior Member

    Hi Seb

    1.Dont electric mix your gelcoat
    2, Dont heat it
    3.Dont use a heat gun to set it off.
    And you will have no pinholes
    Dont mix too vigourously and remember gelcoat is technically not supposed to be more than 1.5 mm thick so that it can flex with the laminate. Dont be afraid to properly brush it out against the mould wall. Its quite acceptable to use a second coat followed soon after the first has gelled.
    Have fun
    Justin
     
  3. Itchy&Scratchy
    Joined: Jul 2008
    Posts: 140
    Likes: 3, Points: 0, Legacy Rep: 117
    Location: Oxford & South Africa

    Itchy&Scratchy Senior Member

    Oh and up your catalyst to two percent and heat the room rather than direct heaton your moulding.
    You also want to keep moisture away from your work area.:)
    J
     
  4. Seb790
    Joined: Aug 2009
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Europe

    Seb790 New Member

    Hi Justin, Thanks for help.

    Ok, I'll make the second half of this mould without warming the gel coat up, and without a heat gun, we'll see. I was warming it up, because unfortunately the gel coat which I have is very dense, I think it's "flows" better when it's warmer. The idea with a heat gun wasn't mine, I've noticed that some people use it because it's easier for them to wet-out glass/carbon cloth, pic1.
    About mixing with a driil, I use slow rpm, I made some experiments and always have less air bubbles, when I mix with a drill than when I mix by hand, I'll try to mix it by hand for a second half, but less vigourously.

    Thanks again.
    Seb
     

    Attached Files:

  5. Itchy&Scratchy
    Joined: Jul 2008
    Posts: 140
    Likes: 3, Points: 0, Legacy Rep: 117
    Location: Oxford & South Africa

    Itchy&Scratchy Senior Member

    Hi Seb
    The secret is to move quickly when coating the mould surface, this will allow the gelcoat to flow . The gelcoats that we use in europe/UK are a lot thicker than the American gelcoats that are usually sprayed. Move quickly and then leave alone, dont go back over it with your brush.

    Gelcoat was originally designed to be hand applied and in most cases of limited moulding runs , usually is. Most often larger articles like boatmoulds are sprayed, and these are sprayed with a specific spray gel which has added styrene to thin it out.

    Also make sure your gelcoat is fresh. As it gets older it gets thicker.
    If you are in the UK let me know and Ill send you my number if you want any other advice.
    cheers
    Justin
     

  6. Seb790
    Joined: Aug 2009
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Europe

    Seb790 New Member

    Justin big thanks for your help:)

    Sometimes I was going back with my brush, if I wasn't happy about coat quality, and that probably was cause of my troubles. I use Enguard GE gel coat, probably made in Italy but I'm not sure about it.
    Thanks again for your help, I'll write a short report when I remove my mould.

    Thanks
    Seb
     
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