Gelcoat thickness question

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PostPosted: Wed Sep 03, 2014 9:06 pm
Just recovered an old seadoo boat (1997 challenger). I started with 600 wet and worked up to 1500 to remove oxidation before buff and polish.
After I removed the factory decals, I noticed yellow outlines where the decals used to be. The 600 wet would not make the lines go away. I then tried 400 and it didnt work. I eventually went down to 150 and after someone heavy sanding the yellowing decal outlines still did not go away! This has led me to believe the yellow stains are fairly deep but im affraid to go to far with the sanding.
How thick is average gelcoat ? Is it possible the gelcoat is stained all the way thru? Any advice on getting rid of it?

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PostPosted: Wed Sep 03, 2014 10:03 pm
Gelcoats, unfortunately are greatly different in thickness from manufacturer to manufacturer. I've seen them as thin as about 6 mils and some past 20 mils in thickness. You are not going to win the battle on this one. The decals prevented the sun from changing the chemistry of the gel coat underneath while all the surrounding gel coat changed completely through itself. This is why most people give up on trying to save the "look" of the factory gel coat. You either end up doing new gel coat or switching to a paint system combo. Guys will do automotive systems above the water line and use some type of "bottom" rated paint below the water.
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PostPosted: Wed Sep 03, 2014 10:34 pm
Great thanks! Ill just have to incorporate the old measurements into the new graphics.
Is there an under water paint you recommend? Boat will never see salt water and never be in the water more then a couple of hours every few weeks in the summer if that makes a difference with automotive paint.

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PostPosted: Wed Sep 03, 2014 11:06 pm
Well, unfortunately I'm not much of a boat guy. Even with that little of a run time I don't think regular auto stuff is going to hold up under that kind of water pressure. A few of the more knowledgeable boat guys had talked about "bottom paints" on here at one time and mentioned some brands. Try it in the search on this page. I'm sure that any local marina could set you up as well.
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PostPosted: Wed Sep 03, 2014 11:21 pm
I did remember the one brand that came up over and over, it was Awlgrip. I did find another site that has some specialty marine paints and had a bottom paints page.... try this....
http://www.bottompaintstore.com/boat-bo ... 3a22b3c39e
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PostPosted: Fri Sep 05, 2014 8:48 pm
Ok so I have been reading about applying gelcoat from a company like fiberglast.com. I want to change the color of the hull from green to blue. I dont quite understand the process of re gelcoating a boat.
From what ive gathered all I will need is a a colored gel coat, then a clear gel coat. Reduced enough to spray out of my gun. Then I can proceed with wetsand and buff/polish like ive been doing. Is this correct?

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PostPosted: Fri Sep 05, 2014 9:30 pm
Yeah, everybody makes it sound pretty easy, huh? First, yes, you went to a good source for gel coats which is fiberglast.com They are a little pricey however they have good tech. support for their products. Putting a gel coat through a regular gun? Not such a good idea if you care about the gun. If that gel coat kicks off in your gun you'll have an expensive paperweight. (Don't laugh, it happens.) There are special gel coat cup guns that lay it on thicker and don't allow that kick-over to happen in the gun itself. Gel coat guns have like a 3/16 inch or larger nozzle for application. Thinning gel coats is not a good idea. For proper performance the stuff should always go on in one shot.
And then there is the cut and buff process, like car paints, uhhh, no. You'll start down at 400 and work your way up. Gel coat is rock hard compared to auto paints so you'll want aggressive compounds and probably twisted wool pads to get the gloss up.
And, yes, when you are all done you will indeed have a nice thick tough coating that still.... wait for it.... fades in sunlight just like the original gel coat did....
I've been buying and restoring kit cars for 42 years now. I've restored gel coats, removed gel coats, but mostly I've just used them as a nice platform to build my new paint system. One of my favorite kit cars, my Bremen Sebring, had one of the best gel coats ever put on a car. It was 20 mils of the brightest glossiest red you'd ever see. Well, that was just after I polished it on a Friday (6 to 8 hours with twisted wool on a buffer) before a car show.... then next day.... hours of bright sun and you could see it "chalking" as the day went on. Gel coats do have a lot of great attributes but sunlight pretty much kills them all over time.
I know you are doing just a jet ski here but I'd go bottom paint below the waterline and auto stuff above....
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PostPosted: Sat Sep 06, 2014 8:08 am
Is it correct i will need a clear over the colored gelcoat? Or ia the color glossy itself? Are there any good waxes you recommend to prolong the shine?

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PostPosted: Sat Sep 06, 2014 10:20 am
Okay, you first have to understand what gel coats were originally intended to do and how they work. They are the first layer sprayed into a mold. A clear gel coat may be sprayed into a mold FIRST because there have been UV inhibitors and blockers added to the newer formulations to help with the known sun problems. Next the color is sprayed into the mold. Notice, we are talking about using the gel coat in a mold? Gel coats were never designed to "air cure" like paints. They must cure in the mold OR you must change these curing properties by adding stuff to make them air catalyze. Fiberglast recommends their Duratec gel coat additive. Your other option is to seal off the gel coat from air with a PVA wax. See, this gets complicated.... that's why I keep coming back to auto stuff.
Nope, no free rides on the wax, not even the polymer sealants will be of much help especially if the gel coat already shows signs of sun degradation.
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