Spraying gelcoat over gelcoat

Discussion in 'Fiberglass and Composite Boat Building' started by alexhiguera, Jan 27, 2005.

  1. alexhiguera
    Joined: Dec 2004
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    Location: Puerto Rico

    alexhiguera Junior Member

    Hi everyone, I know some of you that have been working with gelcoat have my answer, and I am sure many others will be helped also. I am new to the forum ....
    I want to spray on a coat of gelcoat to the entire outside and inside of my 88' Boston Whaler outrage 18'. I have been shooting automotive coats for a while now (emamels, urethanes, polyurethanes etc) but never have tried to spray gelcoat, only to fill up scrapes or dings. Two part polyurethanes is the easy way out recomended by many and the finish is amazing...I know!

    This is all my guess: correct me if I'm wrong!!!!!!
    No prep work over original gelcoat other that fairing and scuff with 200 grit or so?
    MEK with a cloth wiped over old gelcoat will reactivate gelcoat and provide a better bond with the new gelcoat?
    Use a 2.0 to 2.4 nozzle for first two coats providing buildup?
    Final coat with a 1.4 nozzle and at a higher ratio of thinning?
    Air psi from 40 to 80. (less is better to avoid orange peel)?
    Styrene as thinner with wax if gelcoat is laminating or styrene without wax if I have finish gelcoat (that has wax in it already)?
    Wax will rise to surface and block air so it cures?
    First two coats without wax so it remains tacky final with waxed styrene or finish gelcoat?
    Spraying PVA over gelcoat is tricky, better to use waxed styrene or finish gelcoat for final coat?
    Polish with 400, 600 etc all the way to 1200 and then buff with fine rubbing compound?
    There is an additive that allows to spray gelcoat as any other paint and only a buffer is needed to shine after hardening, no sanding required as said before?

    I live in Puerto Rico and this is all a "well kept secret" as not many people do this and those that do don't give many tips or explanations and charge a lot for this kind of work. I found a local gelcoat supplier that color matches gelcoat with any part that you take them. (thats a plus)

    Should I ask for waxed or unwaxed gelcoat giving me the option of waxing it after for final coat with waxed styrene?

    All of this should serve as a outline for those wanting to try spraying gelcoat.

    Alex Higuera
     
  2. DGreenwood
    Joined: Aug 2004
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    Location: New York

    DGreenwood Senior Member

    All looks pretty good...you left out:
    Do not even think about spraying below 65 Degrees F or over 80.
    I say use unwaxed and learn to adjust for temp and humidity with a single type of gel.
    I also think that having the wax seperate from the styrene is better because I use as little styrene as possible. Mostly personal choices.

    Good luck
     
  3. alexhiguera
    Joined: Dec 2004
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    Location: Puerto Rico

    alexhiguera Junior Member

    Spaying gelcoat over gelcoat

    DGreenwood thanks!
    One more thing..I didn't know wax came separate from styrene (parafin right?)
    At what ratio styrene to gelcoat for the buildup sprays?
    At what ratio wax to styrene to gelcoat for final spray?

    I live in Puerto Rico and it is never bellow 80 degrees, ok maybe in the mountain region in "winter" (we don't have winter) meaning December. Is this a problem?
    I live in the coast, 85 degrees at night and up to 100 or a bit more in the day.
    How do I adjust to this, with more styrene to gelcoat ratio?

    Alex Higuera
     
  4. Corpus Skipper
    Joined: Oct 2003
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    Corpus Skipper Hopeless Boataholic

    If that were true, I'd only be able to shoot 8 days out of the year! You can spray over 80, I switch to a slower kicking catalyst, and mix in the lower end, say 2%. No problems. :D
     
  5. alexhiguera
    Joined: Dec 2004
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    Location: Puerto Rico

    alexhiguera Junior Member

    Thanks Corpus Skipper!
    Lets see what others have to say about temps and catalysts...

    About the parafin wax being separate from the styrene, haven't seen it!

    Here it goes...:
    What are the ratios of parafin to styrene for gelcoat to cure properly if I was to add it to the styrene instead of using the waxed styrene?

    Or should I buy a can of regular styrene for initial sprays and a waxed styrene for final spray?

    So you recommend 2% styrene thinning to gelcoat by vol?

    Opinions on spraying PVA over final coat instead of using waxed styrene?

    Alex Higuera
     
  6. Corpus Skipper
    Joined: Oct 2003
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    Location: Corpus Christi TX

    Corpus Skipper Hopeless Boataholic

    2% was for catalyst. Depending where you get your gelcoat from, it may already have wax in it. I don't really thin gelcoat, I pressurize the cup on my gun and it goes through fine. I add a dash of laquer thinner to help it go through also. Comes out great. If you need wax for the top coat, I usually go about 5-10%, but I just eyeball it, no measuring. I don't use PVA so can't tell you anything about it.
     
  7. TrendSetter
    Joined: Dec 2004
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    Location: Annapolis

    TrendSetter Fume Huffer

    Your pretty close for what your talking about. the tip size sounds about right. If it where me doing this in my yard... here is a break down of what i would do

    I would sand down the hull sides with 120 then follow up with 220 and then whipe down the hull sides. its ok to use a DA for all of this and will make the job go quicker. Then once you have all whipped down and ready to go assuming you have it all taped off

    Mix up some gel coat with the wax already in it, add a reducing agent, some times called patch aide or the like.. your local Gel coat place should have this. it will slow down the cure time and still allow you to use the right about of MEKP to cure it off. I would do just one hull side at a time buy the time you get from bow to stern, go back and slap on the second coat. repeat for the other side.

    Let it sit and fully cure since its wax based it will cure up tack free. now comes the fun part get a block or a hard back DA and some 400 and go to town sanding (your gonna have orange peel dont waste your time trying not to) after blocking it all down, get some 600 and 800 for a DA, use both of those.. then finish up with a product from 3M made just for this job, it is a very course polish that removes 800 and up sander scratches.

    It is labor intensive, it would be cheaper to just buy some Awl grip and be done in a day but if your gung hoe for gel coat more power to you. I also dont use PVA anymore using gel coat with a wax addative already in it is hands down way better. If you have any more questions feel free to drop me a line
     
  8. DGreenwood
    Joined: Aug 2004
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    DGreenwood Senior Member

    Yeah Corpus Skipper you are right it is possible to adjust for the higher temp...I was just trying to eliminate as many variables as possible for a beginner. I didn't realize he had such high temps there. Big spray job for a newbie and I would hate for him to have it kick in the gun!

    alexhiguera
    Try spraying some smaller things or practice panels first before you spray your boat.
    Get waxed Gel---forget about PVA
     
  9. Corpus Skipper
    Joined: Oct 2003
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    Corpus Skipper Hopeless Boataholic

    Good point! Refrigerating the gelcoat can help slow this down, but makes it harder to spray. Mix everything else first, and don't catalyze until just before you shoot, and you should be o.k. I tear the gun completely apart after spraying and flush with acetone. My gun lives in a bucket of acetone, only coming out to shoot, then right back in.
     

  10. Kyle
    Joined: Mar 2004
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    Location: Tulsa Ok

    Kyle Junior Member

    Alex,

    Haven't been on the forum in about 6 months, and really jumping in way late. I just shot a 23' with gel coat. It is now late august in Oklahoma. We've had a string of 100 degree plus days. I managed to shoot @ 8 to 12 oz with aprox. 5cc of MEKP. It's all eyeball. no real science. Blasting a bit of acetone thru the gun and wiping the tip off between each round with my left hand, and mixing hardner with my right. My gel coat was already pre-mixed with styrene and wax. I could shoot 2 to 3 cups safely with out it kicking in the gun. After the third, I hauled butt to the acetone bucket to scrub the gun cup and insides. Evrything was all layed out and I had a plan of how I was going to tackle it.
    Now if I only had help with the hard part, sanding.

    good luck,
    Kyle
     
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