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PostPosted: Tue Dec 11, 2012 9:10 am 
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Location: Durham NC
I know I know. Most of these questions have been answered but I want to be absolutely sure before I start spraying. I'm sure most of you understand the reassurance of having others verify what you've learned.

Hull has been completely sanded (Doing one at a time). Chips, dings, and small holes have been filled in with resin/fiber and then sanded down. I'll wipe it down with acetone right before I spray. Room will be in the 70's, ventilation in place, full body toxic suit and respirator, spray gun will be tested to check for good spray. Pressure on gun somewhere between 60-80psi. I am spraying straight gelcoat as my gun has a sufficient nozzle size without thinning. Tested this yesterday with no problems and had a great spray pattern. BTW the Carolina Blue from Fibreglast.com is perfect.

So my spray approach is as follows:
1. Fill two of the 32 oz paper cups with 20 oz of gelcoat.
2. Add MEKP to one of the cups only and mount the cup to my spray gun.
3. Do a quick test spray and then start spraying the boat about 18" away, overlapping on the edges to blend.
4. Do this until I am completely out of gel in the cup.
5. Mix MEKP in the second cup and then finish up the boat with the first coat.
6. Let the first coat dry (a couple of hours maybe) and clean out gun.
7. Repeat for a second coat
8. Third coat will be about 40% Duratec and 60% gel and of course MEKP.
9. Repeat steps above for Duratec/Gelcoat mix.
10. Let that completely dry.
11. Later on wetsand (600 grit?) and polish/buff.

My only real question is, can I lay a coat down and walk away for an entire day? If so I can do a coat a night and it will be easier for me than trying to find an entire day that I can devote to this, although I'll have that soon with the holidays coming up.

Anything I'm missing?

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PostPosted: Tue Dec 11, 2012 9:56 am 
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If it's 70 degrees, and you mix the full amount of MEKP with the gel, then you won't have to wait a couple of hours for it to set up. More like a half hour to an hour - if that.

Only mix what you can use in 10 minutes. You can run successive batches through the gun without cleaning it in between (up to a point). If the gun starts to sputter - stop and clean it immediately.

Shoot one hull, then clean the gun thoroughly with acetone before starting on the next.

Your pressure is a bit high, but it depends on the gun. If you get good results with that gun, stick with it.

Here's a good reference: http://www.evercoat.com/imgs/pis/gelcoat.pdf


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PostPosted: Tue Dec 11, 2012 9:02 pm 
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The manufacturer of Duratec recommends a 50 / 50 mixture of Duratec and Gel coat, and only on the finish coat unless you want to sand between coats :cry:

Remember, when you spray successive coats, let a coat cure to a tacky texture before you apply more, otherwise, you'll have too much wet gel on your hull and it will run. In my limited experience, I've found that more thin coats are better than fewer thick coats. Be patient and don't try to get the job done too quickly. I think if you went straight from one 20 oz cup to another, you'd likely end up making a mess, too much wet gel at once. I'd go with one 20 oz batch at a time. Of course the downside is that applying more thin coats and letting them cure to a tacky finish means that you'll have to clean your gun more often, but that's much better than having to sand the runs out of hardened gel-coat and filling in the thin spots. If you allow 30-40 minutes between coats for the gel to get tacky, you'll have enough of a gap to clean the gun and mix the next batch during the interim period.

What do the rest of you guys think?

I agree with M Bounds that 60-80 psi seems like a lot of pressure for an HVLP (High Volume Low Pressure) system. On the other hand, I don't feel like I ever got the optimal combination of pressure and nozzle size right, so if it's working for you, go for it. What size nozzle are you using? I look forward to hearing what you ultimately decide to do and how it turns out.

Good luck. BTW, Tennessee orange would have been a better color.

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PostPosted: Tue Dec 11, 2012 9:20 pm 
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Location: Durham NC
Thanks for the insights. I'm using the g100 gelcoat cup gun not an hlvp gun and the recommended pressure is 60-100psi. Jeremy? from surf city catamarans recommended 40% on the duretec and I have a feeling he's probably sprayed way more of this stuff than most, so I think I'll go with his experience. And as I stated above that will only be my last coat. I am only going to spray what I need to get one coat down. I wasn't sure if 20 oz would be enough for one coat and that's my thinking of having the second cup ready to go, if I need it. I'll just spray until the coat is finished and then stop.

So it sounds like I need to find a day where I can do all three coats back to back. Is that best as opposed to doing one coat one night, coming back the next night and doing the second coat, and doing the final coat on the third night. Any thoughts on that considering the bottom two layers will be strictly gelcoat? Would I need to lightly sand between coats if I let it sit one whole day even though I've only sprayed gelcoat without wax or duretec?

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PostPosted: Tue Dec 11, 2012 9:34 pm 
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One more thing. After your finish coat has hardened and you've sanded down to 600-800 grit paper, you'll still need to polish the hulls. This stuff from Fiberglast works great: http://www.fibreglast.com/product/Step_ ... ding_Tools. It's a two step process, the second step, 1103 polish, removes the fine imperceptible-to-the-human-eye scratches left by the first step, 1102 compounding paste. Although we are talking about very fine finishes, you can feel the difference between the coats with your fingers.

You'll need a buffing wheel to apply those products. Remember not to use the same pad for successive finer polishes or the residue from a previous application will mar the finer finish that should be left by a subsequent polish. You should find pads specifically for compounding (1st step) and polishing (2nd step) at a good auto body supply or boat shop. Afterwards, give it a good waxing with a quality boat wax that will inhibit oxidation. I use Starbrite waxes with PTEF or McLube Hullcoat. In my opinion, Starbrite is more durable, McLube yields a slightly slicker finish.

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PostPosted: Tue Dec 11, 2012 9:40 pm 
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I would do all the coats in one day. If you leave a tacky gel coat finish to sit all day and night, it will collect contaminates for one thing, but I really don't know what will happen to the finish. My hunch is that it won't be good. I doubt that it would harden all the way even over 24 hours. Sanding would probably be a mess, doubt it would work. Although it might feel hard to the touch, I think that even with slight pressure from the sanding, it would get gunky.

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PostPosted: Sun Dec 16, 2012 10:33 pm 
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Location: Knoxville, TN
Heelcat,

Look at the Division 9 section of the Hobie Racing forum. There's a thread there called 2013 Regatta Dates. Take a look at it and you'll see that several of us in your region are talking about trying to get a bunch of Hobie 16's to show up at one of two regattas held by the Keowee Sailing Club in South Carolina (http://www.keoweesailingclub.com/). It's near Clemson.

If you haven't raced before, don't be intimidated. It's all about having fun and new guys are always welcome. It's a great way to meet other sailors and talk about setting up your boat and discuss sailing and racing. It's an opportunity to learn a lot.

I hope you'll consider joining us and showing off that Tarheel blue boat!

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H14T #47787
H20 #647 (sold)


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PostPosted: Tue Dec 18, 2012 2:09 pm 
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I haven't been on these forums for while, so I just saw this. If you wipe down with acetone, give PLENTY of time for it to evaporate, or you will have pinholes all over it.

When spraying gelcoat, I always liked to thin with Styrene for good flowout, and less buffing.

For buffing, I always used 3M products, and finished with PerfectIt and the 3M convoluted buffer pad. http://solutions.3m.com/wps/portal/3M/e ... QK7NZ8TZgl


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PostPosted: Wed Dec 19, 2012 8:56 pm 
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So I finally got around to spraying with a decent temp outside and the temp inside around 68-72. My first time spraying gelcoat and got a lot of orange peel. Part of the learning process I guess. I assume from here I can save the coat with some sanding and buffing. What grit should I start with and how soon after spraying should I start sanding? Wll it make a difference if I start sooner rather then later? At least it's only one hull.

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PostPosted: Wed Dec 19, 2012 10:24 pm 
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The first boat I did was my Hobie 20 two years ago, I had minimal orange peel and minimal sanding. The second boat, just this past summer, was my 14 and although I did everything the same, as far as I could tell, the 14 had a significant amount of orange peel. But a lot of sanding followed by compounding and polishing made her just like new. You can recover from fiberglass issues with enough time and sand paper.

Now to your problem. If the first coat had wax or Duratec in it or was covered by PVA, then let it harden all the way before you sand. I allow 24-hours before sanding, although that may be overkill. The last thing you want to do is attack gel-coat that isn't fully hardened with sandpaper. It'll make a gummy mess. If your current coat hasn't been mixed with a hardener and will only harden to a tacky finish, I'd spray it again, and put a couple more light coats on it, with a 30-45 minutes between applications. Mix Duratec into the last coat. This will allow you to have a thick coat under the orange peel so that when you do your inevitable sanding, you can sand it smooth and still not go all the way through the new gel-coat. If you go through, it isn't a big deal, just spray on a little more gel for a patch, let it harden, then fair it back in with more sand paper.

For smoothing out orange peel, I used an orbital sander with 200 grit paper and whet successively finer from there.

When you start wet sanding at 400 grit or finer, run an air driven sander off your compressor. You obviously don't want to use an electric sander for wet sanding unless you like getting zapped. I got a cheap one from Harbor Freight and it worked great.

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PostPosted: Wed Dec 19, 2012 10:38 pm 
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I've already sprayed all three coats and the last one with duretec. So should the 200 be dry? And then wet sand at 400 and work my way up?

Cool another toy to buy. Don't tell my wife.

Any ideas on not spraying orange peel on my second hull? I'm using the g100 gelcoat cup gun with a 4.5 nozzle. The 2.7 was way to small and wouldn't spray even with the duretec. Gun says to use 60-100 psi. It is not an hlvp gun. I seemed to have less orange peel around 80 than 60. Didn't try 100. Might order the 3.5 nozzle to see if that helps.

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PostPosted: Thu Dec 20, 2012 5:20 pm 
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Orange peel can be from acetone not dissipating away, if you wipe with it. Also, it can be from the gel kicking before it flows out. Thinning with styrene not only lets it flow more freely, but it postpones the kick a bit, allowing it to flow out really nice. I can't tell you what percentage to thin. I just do it by feel.

I have all sorts of spray guns, but get my best gelcoat results using old style Binks siphon feed guns. They're pretty easy to clean too. I use a supplied air system that I made up from a disposable supplied air tyvek hood, and a medium sized new ShopVac (used only for this purpose) with extra hose. The vac sits outside the shop in clean air, and its of course set to blow instead of suck. I have to tie the hood on my head or it will lift off-keeps your head and face nice and dry too. You do get some mist in the air with this system, but most of the time I don't even have to wetsand heavier than 600, if at all, and it buffs out like a dream.

I cool the shop down to 65 for gelcoating and raise it to 72 to cure after it's shot.

A light mist of water on the floor from a water hose keeps any dust down from feet. I keep polyethylene sheet to enclose a large space to keep the overspray off of everything else.

A set of four small sawhorses that support the boat upside down at a comfortable working height are well worth the little effort it takes to make them. I spray the bottoms first, and then the tops.


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PostPosted: Thu Dec 20, 2012 7:56 pm 
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Well I hand sanded a couple of spots where the gel coat dripped on the boat to see how it would look and it sanded down very nicely The orange peel sands right out. Looks like it will be a fairly straight forward sanding , wet sanding and buffing. Tedious but doable. Gel coat is quite forgiving. I have my work cut out for me!

Here's some more pics with the bottom part sprayed. Still have to spray the top. The blue doesn't come out as well in the pictures as it looks in real life. But it's a pretty good carolina blue.

The white'ish area you see in the second picture is one of the spots I sanded so it looks milky as its only been sanded with 200 grit dry. It is not through the gelcoat.

Image

Image

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PostPosted: Sun Dec 23, 2012 6:55 am 
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I sanded the 200 dry to remove the orange peel, then started wet starting with the 400. A cheap electric orbital sander will cut dry sanding time immensely. Be sure to wear surgical mask to keep from breathing all the dust. Go with a pneumatic sander for the wet sanding - electricity and water don't mix.

I think the differences in my HVLP gun and your setup make comparisons of nozzles like comparing apples to oranges. When I shot my Duratec mixture it flowed smoothly through a 2.0mm nozzle. I don't think I can tell you much about how to do it with your system. I'd listen to Tom King. I think he's right on with the advise regarding acetone. On the second boat I sprayed and had orange peel issues, I had thinned my initial coats with acetone. I will never, ever, ever thin gel-coat with acetone again.

The Tarheel blue is looking great. You should consider leaving the decks white. After all, the away jerseys are white. Just clean the decks up and coat with Poli Glow. It flows smoothly over the non-skid and preserves the pattern for a clean factory-new look. That approach will save you a ton of work. I'm a big fan of legacy two-tone combinations. My 14 has blue decks on white hulls.

I hope to see that great looking boat at some Division 9 regattas next season.

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H14T #47787
H20 #647 (sold)


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PostPosted: Mon Mar 18, 2013 8:42 am 
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We finally had a break in the weather here in NC and it got warm enough for me to spray the final section of my boat. I'm finally done gelcoating and now I just need to do the final sanding and polishing. It actually wasn't that "hard" of a job, it's mostly just very time consuming. Get to know and love your orbital sander is about all I can say. The actual gelcoating was the easy part. It's all the prep beforehand and afterwards that makes it a PITA. Unfortunately I am moving when I get back from Mexico so I won't be able to get out on the water until probably May. I also have to get the boat completely back together but that should only take a few hours from here, well except the tramp lacing.

Due to the unreasonable cold weather here I also ended short on time for painting everything except the blades black as well. The new home purchase also is not helping in purchasing a new black trampoline. I guess I'll save that stuff for next year and just worry about getting out on the boat now that the weather is hopefully getting and staying warmer.

Thanks for all the tips and advice. Hope to see some of y'all out on the water soon.

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