Pinholes in my finishes >:O

Discussion in 'Boatbuilding' started by Carbonman, Aug 3, 2009.

  1. Carbonman
    Joined: Aug 2009
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    Carbonman Junior Member

    So first off Im new to the forums and I know I should use the search and I have. But I wanted answers specifically to mysetup. It woudl make me feel at ease :p

    So heres a quick runup of how I layup my parts.

    I have a clearn taped and prepped mold. I lay over 3 layers of carbon fiber fabric followed by peel ply, green mesh flow media, peel ply again, and a boarder of breather. spiral wrap with vacuum at one side and a small tube that lets the resin in from the opposite side.

    I start off by turning the vacuum on for at least an hr before letting in the resin and when I do let the resin in I do it slowley to saturate everything well.

    I do check for leakes and double bag the product to secure myself from any air leakes.

    I let the resin in and all goes well. I see tiny air bubles and try to push Them to the edge but nothing goes.

    I let the part cure before I pull it out and when I do BAM a few to a dozen pin holes :(...

    I tried epoxy resin thinned with laquer, epoxy resin straight but its kinda thick, and I tried polyester resin.

    The surface has to be clear so I cant use any kind of colored gel coates. But if I try a clear gel coat I am certain I will still have air pockets with in the visible top coat instead of pin holes. At least pin holes I can fill them in with clear. Although that does take extra time. I think why not just deal with filling each one in afterwards and just clear coat over it then sand it smooth. Well Id like to have the parts come out nice the first time to speed things up.

    If anybody can help me Id much appreciate it :D

    Look forward to spending hrs and hrs on these forums!
     
  2. Carbonman
    Joined: Aug 2009
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    Carbonman Junior Member

    It also just hit me. Can I dip my products in clear? I was thinking of that but the amount of clear Id be wasteing... Then again I could just brush it on thick? What kind of clear should I use? Will urathane clear fish eye?
     
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Are you using a low viscosity laminating resin?
     
  4. Itchy&Scratchy
    Joined: Jul 2008
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    Itchy&Scratchy Senior Member

    A lot of carbon product manufactures spray their finished articles with clearcoat which also helps with uv protection to stop yellowing, it should also help with filling small bubbles.

    Some folk advocate using a 'gelcoat' of epoxy before laying in the cloth. This could be either straight epoxy or thickened(which can end up milky), which should eliminate bubbles. Dont mix too vigourously though, this will also result in bubbles.

    Hope Im not underestimating your skills- its difficult sometimes to judge just how much experience people have when posting and i dont want to offend.

    cheers:p
    Justin
     
  5. Jimbo1490
    Joined: Jun 2005
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    Jimbo1490 Senior Member

    You can't thin epoxy with a solvent in a closed mold system! The Epon SU-3 system used MEK but then that was intended for prepreg manufacturing on heated open rollers. If your resin is too think, you need to use a different formulation.

    Neat epoxy resin is available in partially cured sheets (stored frozen like prepreg) if you want to add a clear epoxy without screwing up the fiber fraction. You could lay these in the mold first then lay the cloth over them, infuse then cure. These have to be cured at elevated temperature, of course.

    Jimbo
     
  6. aboyd
    Joined: Jul 2009
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    aboyd Junior Member

    I was watching a tv show not to long ago, about building C.F. auto parts all of there mixing was done under vaccum. They said it was to prevent bubles in the resin. Might be something to consider.
     

  7. mastcolin
    Joined: Jun 2005
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    mastcolin Senior Member

    i imagine the pinholes are where the resin doesn't wet the cloth out good.

    You have a vacuum, you don't have zero air in bag (think about how much air would take to make a pinhole- it won't be much). Even if you have a 100% vacuum then i suspect the pinholes can just be caused by the resin not wetting the cloth completely-a pinhole of zero air ie where something causes the resin not to flow.

    I'd suggest the only solution is to topcoat after taking it out the bag (failing trying differing combinations of cloth and resins to see if this wets/lows better)

    ps "epoxy thinned with lacquer" ??? this sounds bad idea. thinning with anything sounds bad idea. The solvent will evaporate at room temperature under a vacuum casuing bubbles as it cannot escape. Which now has me thinking that under vacuum all sorts of stuuf may be evaporating out of the resin mix. eg water boils at 100c at 1bar atmosphere. At lower pressures it boils at lower temperatures. In reverse think LPG. (p=v/t...i think from 20 years ago chemistry degree) Do you know you cannot boil an egg on top of mount everest...and that is not because it is cold:)
     
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