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Thread: Spraying Gel Coat

  1. #1
    Senior Member Don's Avatar
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    Spraying Gel Coat

    I have a question, for you fiberglassing experts out there.

    In all my fiberglassing experiences with the car to date, I have been laying gel coat down with a brush. It has been easy enough to do it this way but it doesn't always produce a nice even coverage on the final piece. Never been an issue till now as I have been sanding and working all the pieces after the fact anyway.

    I now want to try my hand at spraying the gel coat in to the molds I have to see how much different of a result I get. I am expecting to be a much better finish since I will have more even thickness and coverage than with a brush.

    OK, now finally to my question.

    When spraying gel coat, what size nozzle is best to use? I have a small finishing air spray gun I want to try to use but I am not sure on what size tip to go get for the gel coat.

    Do I also reduce the gel coat down? I would think not just a larger nozzle to handle the thicker liquid. If I do need to reduce the gel down, with what do I reduce it?

    Any help would be greatly appreciated.

    Thanks
    Don
    308 Ferrari replica
    Prova Countach 5000QV

  2. #2
    Senior Member jdorr2002's Avatar
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    Re: Spraying Gel Coat

    large tip yes, or a cup gun, reduce with acetone @ 25% for spraying

  3. #3
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    Re: Spraying Gel Coat

    theres gel coat that you can buy that is ready for you to spray and you dont have to reduce.

  4. #4
    Senior Member MacGyver's Avatar
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    Re: Spraying Gel Coat

    Don,
    You could use a regular spray gun with about a 2.0 tip. The drawback is spending an hour cleaning the gun when you are done. If the gelcoat hardens before you can clean the gun. You might as well throw it away or spend all day clearing up the passages.
    i would recommend The ES G100 gelcoat spray gun. Designed to hold one quart throw away cups. I ordered mine for 119.00 + shipping from http://www.uscomposites.com



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  5. #5
    Junior Member Enjoi's Avatar
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    Re: Spraying Gel Coat

    Don,

    The ES100 dump gun suggested above is a great recommendation, it will give you a good, even amount of material coverage. In regards to reducing however, use a product called Styrene and reduce your gelcoat to about 15% per volume, not acetone.

    Acetone is great for cleaning your equipment when you're finished because of how harsh it is. Using it to thin the gelcoat so that you can spray it will work, but it actually corrupts the chemical properties of the gelcoat and produces a weaker end result. Styrene however acts with the chemicals that make up polyester gelcoats and resins instead of against them, so Styrene actually allows the purpose built chemical makeup to remain... just in a thinner, more sprayable form.

    Hope that helps.

  6. #6
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    Re: Spraying Gel Coat

    Quote Originally Posted by MacGyver
    Don,
    You could use a regular spray gun with about a 2.0 tip. The drawback is spending an hour cleaning the gun when you are done. If the gelcoat hardens before you can clean the gun. You might as well throw it away or spend all day clearing up the passages.
    i would recommend The ES G100 gelcoat spray gun. Designed to hold one quart throw away cups. I just ordered mine the other day for 119.00 + shipping from http://www.uscomposites.com



    I have a regular Magnum Venus gel coater but I usually just grab this same GS gun Mac has here. I don't reduce. I like the way the "dump" gun puts it on unreduced.

  7. #7
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    Re: Spraying Gel Coat

    A poorman's method is to spray unreduced gelcoat through a schultz [or undercoating] gun. It really wacks on a heavy coat so be careful not to allow it to build up too thick or it may crack or lift.
    I never liked reducing gelcoat. I feel you are taking away from its high viscosity positive characteristics.
    I have sprayed it unreduced through a regular auto paint spray gun but only with the use of a pressure pot. [Air line pressure at the pot and air line pressure at the gun]
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  8. #8
    Senior Member Don's Avatar
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    Re: Spraying Gel Coat

    Thanks for all the great help guys. I think I will go see if I can find that gel coat gun locally and have a try at that.

    I just wanted to see about getting nicer coverage for the headlight buckets as I am done the first mold and pulling a piece out shortly to see how it all turned out. I plan to just do the brush method for my first pieces and I sort the molds and end pieces out before getting into it.


    Thanks again.
    Cheers
    Don
    308 Ferrari replica
    Prova Countach 5000QV

  9. #9
    Senior Member MacGyver's Avatar
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    Re: Spraying Gel Coat

    Just an added note on using the Es 100 gel coat gun. I found that Using yogurt one quart plastic containers works like a champ. Obviously, without the yogurt!!! :
    Once you use the container with the gelcoat. Let it harden in the container pop it out and reuse the container again. That way you don't have to keep eating all that yogurt.

  10. #10

    Re: Spraying Gel Coat

    1.8 to 2.2 tip will work good with a conventional or hvlp spray gun.&#160; I wouldn't recomend thining 25% with acetone.&#160; IMO that is way to much acetone and will change the properties of the gel coat.&#160; Thin with 5 to 10% acetone.&#160; It will still spray out good.&#160; Clean your gun with acetone when done... quickly.&#160; I only mix about 1 pint of gel coat at a time so it doesn't start curing inside the gun.&#160;

    In between filling up the gun spray a little acetone thru it.&#160;

    Also if your doing fiberglass work try using vinyl ester resin as it is much more dimensionally stable resin than polyester which shrinks too much.&#160; I even use vinyl ester for mold building because it holds it's size very well without shrinking.
    Vinyl ester works the same process as polyester resin ... uses mekp , fiberglass rollers and brushes. It cures at the same time rate also.

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