more gelcoat spraying-specific to gun/setup

Discussion in 'Materials' started by ianmoore, Nov 17, 2021.

  1. ianmoore
    Joined: Nov 2021
    Posts: 5
    Likes: 0, Points: 1
    Location: Vashon, Wa

    ianmoore Junior Member


    Don't mean to cross post, so figured i would post a more general query.

    I am in that weird zone of rarely gelcoating, thus not wanting/able to have top notch equipment. I have a little bit of experience, having sprayed my top hull a few years ago. I would give myself a "fair" in outcome. I was a little loose in the way I did it, and had the respected results.

    This time I am set up better. I have the boat in a garage where I can control temp and humidity. The challenge will be that I am spraying the bottom of the hull. The boat is on blocks and stands. I can't flip it.

    I bought a cheap, but more appropriate gun. It's a chinese gun, similar to many of these type. It seems to be decently made. It has a 2.5mm tip. I'm running it off of a comp that delivers 6.4 CFM at 40. The gun needs 35-50 PSI and uses 2.5-3.5 CFM. I have a couple of filter/driers, including one right at the gun.

    I initially posted about a patch i was gonna do. I needed to do the patch, but also wanted to use the area to dial in the gun. I tried the first pass at around 40PSI. I shot 6 oz, thinned with 10% MEK. I added 2% wax and 2% catalyst. Temp was around 68-70 and humidity was 55%. I had the spray control valve about halfway open and the fluid control valve mostly open.

    The material went on reasonably well. The pattern looked good. I did notice a decent amount of orange peel. I got a message from the Fiberlay guys(after I shot it) that I should only thin to 5% if possible.

    I am wondering if there are any obvious changes you would make in terms of conditions or mixing to try to get a smoother layup?


  2. ianmoore
    Joined: Nov 2021
    Posts: 5
    Likes: 0, Points: 1
    Location: Vashon, Wa

    ianmoore Junior Member

    I don't know if the pics will be helpful, but here is a closeup and another for scope IMG_1313.JPG IMG_1314.JPG
  3. ondarvr
    Joined: Dec 2005
    Posts: 2,739
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    Location: Monroe WA

    ondarvr Senior Member

    The cheap guns work fine for gel coat, a good one with the a 2.5mm tip on Amazon is about $35.

    Gel coat isn't formulated to work like paint, so getting it to flow and level well isn't something it's going do without some help.

    Duratec clear additive will help you get closer to a good finish, the more you add the better it will level and flow. You risk losing some of the gel coat's ability to hide underlying colors if you add too much though.

    This amount will change with every color and brand of gel coat, so test it first.

    It still won't be perfect, but much closer to what you want, so far less sanding is required.

    Gun adjustment is something you need to play with, there are no exact right or wrong settings, it's just what works for that specific spray job.
  4. ianmoore
    Joined: Nov 2021
    Posts: 5
    Likes: 0, Points: 1
    Location: Vashon, Wa

    ianmoore Junior Member

    I went ahead and sprayed the boat without Duratec. It's an imperfect situation, but overall pretty happy with how the gelcoat sprayed. I have the boat up on stands(couldn't flip it) so am having to spray at some weird angles. I'm not gonna do much sanding on the bottom, focusing more on where it is visible, like coming up the bow line. I had the best luck with the fluid control open, the gun around 45 psi(max is 50). It shoots pretty well to my limited experience, and the biggest challenge was trying to shoot upwards.

    I have a couple of funky spots where the cup of the gun grazed the wet coat. I tried sanding it out in one spot and got back to the fiberglass. One spot looks like a long shallow gouge. Should i just use a gel-paste in these spots? Seems weird to spray for such a small area.

    Speaking of sanding, I have a DA(on a GFCI) with a soft backing plate and a bunch of wet/dry sandpaper. I experimented along the bow line with some 600G. Was trying to see how long it would take to get any imperfections out. I found the 400G seems like a better starting place to macro, then switching to the 600 when i can barely see the shadows. Still a lot of work

  5. KD8NPB
    Joined: Mar 2018
    Posts: 106
    Likes: 20, Points: 18
    Location: South Carolina

    KD8NPB Senior Member

    Use PPS cup system, it will spray at any angle.
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