Gel coat spray systems

Discussion in 'Boatbuilding' started by Synapse, Mar 11, 2008.

  1. Synapse
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    Synapse New Member

    Hello all

    I am a tutor within the design department of London South Bank University; we are looking to expand our plastics capabilities;

    We could achieve some much finer finishes to projects with a gel coat spray system.

    Does anyone have any recomendations as to good air-fed gel coat spray systems?

    Thanks
     
  2. tinhorn
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    tinhorn Senior Member

    I presume you're brushing gelcoat into the molds now. Until you get your new spray system, you'll find that adding a bit of gelcoat to the first layer of laminate will hide the inevitable streaks. Doesn't take much - maybe 10% gelcoat to resin.

    Your supplier could turn you on to new equipment, but I liked my cheap, home-brew system -- a 2-1/2 gallon pressure pot connected to a primer paint gun with about six feet of hose. Pressure regulators on both pot and gun. This allowed me to use one-gallon plastic milk jugs so that I didn't have to clean the whole pot. For larger projects, I just lined up gallon jugs (up to five or six) and when one ran out, I'd catalyze the next one, put it into the pot, and keep on spraying. This would work for dinghy-sized projects, but not a yacht.
     
  3. Synapse
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    Synapse New Member

    Thanks Tinhorn,

    You're right, we are just brushing it on at the moment. Not ideal, especially with regards hairs falling out of the brushes and getting set into the coat!

    We have a pressurised air line to run air tools off, so can use spray guns with that. Is any old air-fed gun ok to use with gel-coat, or do you need a particular type of nozzle? or a particular type of gel coat that sprays more easily?
     
  4. the1much
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    the1much hippie dreams

  5. tinhorn
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    tinhorn Senior Member

    Cup guns are okay for touch-up, but to spray a mold of any size, you'd spend all your time replacing the cups!

    You can use your current air line, but install a moisture trap so that water or oil won't get into the spray gun. You DO need a gun with a larger tip than is used for paint. I bought a primer gun with a larger tip and it worked beautifully. If my shop was too cold and the gelcoat was too thick to spray nicely, I thinned it just a tiny bit with acetone even though anybody worth their stir stick will insist you should never do this.
     
  6. the1much
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    the1much hippie dreams

    hehe,,,,we used ta spray out 55' and bigger,,,,bosses said it was cheaper getting an extra guy to mix for ya then it is to buy a spray systems themselves were worth,,,and i always like having "moral support" so is what i've always used,,hehe ;)
     
  7. waikikin
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    waikikin Senior Member

    Synapse, I use a Polycon "cup" gun, but the tubs it uses hold up to 2kg although wth 1.6kg it goes better(less weight to hold up), it has a 6 or 8mm tip & the gelcoat passage is only 25mm long & strait so easy clean in a small tin of acetone- the spray head dunks right in & a pipe cleaner or similar swipes the gel out. I've shot up to 25m2 using multiple tubs preped up before & catalysed as you go, about 110 grams of gel hangs back in the tub so you gotta factor that in your prep & I tag up the perimeter of the job to set the meters squared per tub. It cost about $300A maybe 10 years ago, also be aware that your gunna get heaps more styrene stink when you spray so there might be some issues there, if the jobs are small you can make a little gelcoat "puppy" out of an air blow down gun with a T on the front & venturi the gel up a short pipe(depth of cup)& hold the puppy & cup in syncronicity as you blow it at the job.You can also use a gravity style(cup on top) conventional spray gun, I got a Star brand(Asian Iwata copy) with 2.8mm tip, it goes good but slow & you gotta rush to clean before the gel sets inside it. All the best from Jeff.
     
  8. Landlubber
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    Landlubber Senior Member

    Most any putty gun will spray gelcoat quite well for small to medium work. Thin with styrene.
     
  9. the1much
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    the1much hippie dreams

    i was thinking,,,,since their using a brush now,,,,they cant be doing anything with any size to it,,,,so maybe they should get a cup first,,(its better to ruin your first gun if its cheap) and try it all out,,and if it works for them,,,,move on to a bigger "system"
     
  10. tinhorn
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    tinhorn Senior Member

    I developed a dislike for cup guns after dribbling over the top of the cup a few times. Nothing spoils a nice spray job like a big glob of gelcoat. If you don't need to be a contortionist to gelcoat the mold, they might work okay.
     
  11. the1much
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    the1much hippie dreams

    and not spraying the gel onto the project "last" helps,,,,,if you got a mould,,and spray first,,,then dribbles shouldnt be a problem,,,but he isnt very clear on his situation,,so i think he just wants us "guessing",,,hehe ;)
     
  12. SamSam
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    SamSam Senior Member

    What's a putty gun?
     
  13. the1much
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    the1much hippie dreams

    i was wondering same thing,,,but didnt want you guys throwing crap at the "old hippie" hehe ;)
     
  14. Roly
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    Roly Senior Member

    "Most any putty gun will spray gelcoat quite well for small to medium work. Thin with styrene."

    Hey LL,
    Do you have any problem with gelcoat yellowing with Styrene?
    We had a yellowing problem (clear resin & styrene) with surfboards years back. Is there any alternative?
    Cheers
     

  15. Fanie
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    Fanie Fanie

    Hi Roley, what's a putty gun ? Gravity feed spray gun with an oversize hole ?

    The idea of gellcoat is to go on thick, if you spray it on you may not get the cavities (finer ones) filled better, I tried it once and I wasn't impressed. You get better results by giving more attention to the special areas.
     
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