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Old 27-08-2013, 19:31   #31
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Re: Gel Coat Color Match

It looks totally different when you do it properly with squares of nice mylar, but heres a pic of a match with cigarrette cellophane, which is what I cadge for matching if I have no mylar handy. I think the top right is the match but you probably have to blow it up to see anything. I'll find better pics later.
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Old 27-08-2013, 19:40   #32
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Re: Gel Coat Color Match

Ooo... I have to try that mylar thing on our next job.

Also, +100000 on the preval sprayers. One thing I didn't see mentioned about those is that you can use a preval sprayer over a couple of times if the canister isn't used up. Clean the bottle with acetone, put a bit in the bottom and screw the sprayer back on, then spray it into a rag with the nozzle covered. The acetone should start bubbling in the bottle, that means it's working. Once you've managed to pass enough acetone through the canister to clean it, it should be safe to spray again later. Not a huge deal, but there's only one supplier of them up here and they take FOREVER to get more in.
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Old 27-08-2013, 19:48   #33
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Re: Gel Coat Color Match

Quote:
Originally Posted by AbaftAndBaffled View Post
Ooo... I have to try that mylar thing on our next job.

Also, +100000 on the preval sprayers. One thing I didn't see mentioned about those is that you can use a preval sprayer over a couple of times if the canister isn't used up. Clean the bottle with acetone, put a bit in the bottom and screw the sprayer back on, then spray it into a rag with the nozzle covered. The acetone should start bubbling in the bottle, that means it's working. Once you've managed to pass enough acetone through the canister to clean it, it should be safe to spray again later. Not a huge deal, but there's only one supplier of them up here and they take FOREVER to get more in.

You'll like it. Make sure you get clear mylar. It's like cheating.



We use a lot of these with a teeny pancake compressor too, barely any air required. Cheap enough to be disposable if you waste one. Sprays a whole lot nicer than a Preval.


Tool Force A-C7 Touch-Up Spray Gun - Amazon.com
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Old 27-08-2013, 19:57   #34
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Re: Gel Coat Color Match

You want the 2 oz. jars of pigment. Yellow oxide, black, bright yellow, pthalo blue, green, and red are enough for the majority of colors. A well cared for tint kit like this will last a casual user a lifetime.



http://www.fiberlay.com/prod-polyest...06&startrow=15
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Old 27-08-2013, 20:22   #35
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Re: Gel Coat Color Match

I appreciate any info on Gel Coat.

My hull/deck is a very light tan/ivory color and the non-skid is slightly darker. I have some spider cracks in the deck and non-skid that I want to try repairing myself. So any info on materials, sources, etc., would be very much appreciated.

Thanks for the info.
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Old 28-08-2013, 08:06   #36
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Re: Gel Coat Color Match

Thanks to minaret & cabo_sailor.
Here is a summury of their Gelcoat color matching.

Matching gelcoat color is an art. Sometimes you get lucky and hit it in 15 minutes and other days it can take more than an hour to get a perfect match.

1) You can get Gelcoat tints from Fiberlay. You can also use Universal tints, but I like to stick with tints designed for gelcoat. Order from Fiberlay or find a local source.

2) Prep and polish a spot near the repair area. I always find a spot that I sand and buff until I've exposed like new gelcoat and use that as my palette. A color can vary dramatically from bow to stern due to less than perfect mix in the drum at the factory. You are trying to restore the original color so you can match to it. Sometimes you can find the inside of a hatch or something which has not been exposed to weather and that can help.

3) Try to do the gelcoat match in the shade and make sure you have had your sun glasses off for at least 30 minutes. Thin the devil out of the new gelcoat your mixing with MEK to be sure that any pigment totally dissolves.

4) Take it very slow because a little pigment can go a long way. On my boat it takes about 6-8 drops of pigment per quart to match.

5) Here is minaret’s secret tip. Once you have selected and prepared your spot, acquire a piece of clear mylar film. Cut it into one inch squares. In a pinch cigarette cellophane works fine. Put a daub of prospective color match onto your prepped area. Then take a square of the mylar and lick one corner to get some spit on it. Put the dry corner onto your daub of gell. You will see a clear demarcation line between the spit and the gell. Gently rub the mylar until the spit line touches the gelcoat. You will be able to see even the smallest color difference using this technique. I can't explain why it works, but iff you try it you will see why this is the deepest darkest secret of the color matchers art. With practice anyone can match better than any spectrograph.

6) Stick to it and you'll get it. Try using yellow umber and burnt sienna. These along with a little bright yellow, red, and black, are the usual suspects for getting most shades of white. Be careful with the red and black. Both generally need less than a drop. I generally use a sliver broken off a stir stick for getting a micro drop. Almost all whites need a hint of black.

7) Since you are not adding any catalyst, the gelcoat won't harden and you can clean your palette from time to time with a rag and a bit of acetone.

Another good tip for the amateur is to do your match and then blow a little tiny patch of it on your prepped match zone, wait for a cure, and polish it to make sure it cures in the direction you expect and is a good match. This can save you from making the mistake of shooting a large repair that doesn't quite match

8) After you have a good gelcoat color match, then fair out your repair area and with a Preval sprayer you can now spray your gelcoat. Add wax in the last coat or finish with a coat of PVA (polyvinyl alchol). Spray the first coat over just the repair and each successive coat slightly larger. You can get a preval at home depot. Buy several, they are cheap. Heat the preval with a heat gun in-between coats and it'll spray better. Hot water immersion works too if you don't have a heat gun. Don't heat the gelcoat though, just the spray canister. Finish with 600 wet then 800 wet. Then polish with 3M super duty. If your color match and prep work is good it'll look like new.

Gelcoat is normally sprayed on in multiple coats to achieve the final cured thickness. You want enough thickness to allow for the initial sanding and polishing process, and still leave enough thickness to last a decade or more of maintenance compounding and polish before getting too thin.

The cured thickness you want prior to initial sanding is a minimum 30 mils & max 35 mils. This will allow for a 5 - 10 mil thickness reduction, leaving around 20 - 25 mils after polish. Any heavier than 25 mils and you'll run the risk of spider cracks in a few years. Gelcoat continues to cure and shrink through out its life span. Standard maintenance will reduce your thickness by about 2 - 3 mils a year if you do a semi annual compounding & polish on top side surfaces & 1 - 2 mils for an annual hull maintenance.

You should be able to spray 10 mils per application & allowing for shrinkage in the initial cure, this would be 4 applications. The application schedule would be as follows:

1. 10 mils gelcoat - little or no additives* & no surfacing wax
2. 10 mils gelcoat - little or no additives* & no surfacing wax
3. 10 mils gelcoat - with additives* & surfacing wax

Allow the gelcoat to harden for several hours between coats. Coat 1 & 2 will be tacky after hardening to the point that you can't put much of an impression in it with your fingernail. Coat 3 should have no tack at all at the same point.

The surfacing wax will migrate to the surface as the curing cycle takes place and create a barrier to air. This is necessary for a tack free surface when cured so that you can sand.


Thanks again to minaret & cabo_sailor
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Old 28-08-2013, 08:21   #37
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Re: Gel Coat Color Match

Nice summary, thanks man. Don't forget to prep extremely thoroughly with 400 well out past the repair to prevent halo.
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Old 28-08-2013, 08:32   #38
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Re: Gel Coat Color Match

Here is another little hint. Take a sample to home depot and get it scanned. They will give you a relative formula which can be a good place to start.

I have never had any luck with those sprayers. Gelcoat is to thick to spray and when I thinned it with acetone it never looked right.
I now use a foam brush.
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Old 28-08-2013, 08:39   #39
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Re: Gel Coat Color Match

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Originally Posted by S/V_Surya View Post
Here is another little hint. Take a sample to home depot and get it scanned. They will give you a relative formula which can be a good place to start.

I have never had any luck with those sprayers. Gelcoat is to thick to spary and when I thinned it with acetone it never looked right.


Thin with MEK and/or styrene monomer. Acetone causes porosity and evaporates too quickly anyway. You can watch the Zahn cup readings change by the minute. Never reduce gel more than 10% with anything.
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Old 28-08-2013, 09:53   #40
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Re: Gel Coat Color Match

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Originally Posted by minaret View Post
Thin with MEK and/or styrene monomer. Acetone causes porosity and evaporates too quickly anyway. You can watch the Zahn cup readings change by the minute. Never reduce gel more than 10% with anything.
MEK is the hardener, yes??? I never found a source for the styrene monomer. I guess I should heve looked harder for it. Also, my gel coat sets up quickly and that is a problem with a sprayer. I am interesed in how you handle these situations. Since posting I did look for some youtube videos on get coat repair and sprayng but to date not much help.
Thanks
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Old 28-08-2013, 09:53   #41
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Re: Gel Coat Color Match

Looking at the Fiberlay website, I can see it could be easy to spend plenty of $$.

I'm looking forward to giving it a try when I work on my boat in the future.
Thanks for the info guys.
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Old 28-08-2013, 09:57   #42
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Re: Gel Coat Color Match

Quote:
Originally Posted by Cotemar View Post
5) Here is minaret’s secret tip. Once you have selected and prepared your spot, acquire a piece of clear mylar film. Cut it into one inch squares. In a pinch cigarette cellophane works fine. Put a daub of prospective color match onto your prepped area. Then take a square of the mylar and lick one corner to get some spit on it. Put the dry corner onto your daub of gell. You will see a clear demarcation line between the spit and the gell. Gently rub the mylar until the spit line touches the gelcoat. You will be able to see even the smallest color difference using this technique. I can't explain why it works, but iff you try it you will see why this is the deepest darkest secret of the color matchers art. With practice anyone can match better than any spectrograph.


8)If your color match and prep work is good it'll look like new. However, your color match almost certainly will not be good.
Thanks guys for all the info, I am a little confused on step 8 and step 6. As per step 8: are you saying that even if we follow these steps the color match won't be good? I thought this was how you color match successfully?

Also, the Mylar trick: So what you are saying is that by putting the film of Mylar over the uncured gel coat and over the original gel coat you are getting a much more accurate comparison of what it will look like cured than you do if you are just looking at a dollop of gel coat on the hull?

Two more questions

Now that you've put all this effort in to color matching how do you transfer the match over to subsequent repair jobs? Do you just try to make the batch big enough that it will last the entire job or do you have to repeat the matching process every time you start a new job?

And finally: is there an issue with doing gel coat outside? You recommend doing it in the shade, but most paint manufacturers recommend painting indoors in a controlled environment.

Again thanks for all of the info.
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Old 28-08-2013, 10:07   #43
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Re: Gel Coat Color Match

Quote:
Originally Posted by minaret View Post
You'll like it. Make sure you get clear mylar. It's like cheating.



We use a lot of these with a teeny pancake compressor too, barely any air required. Cheap enough to be disposable if you waste one. Sprays a whole lot nicer than a Preval.


Tool Force A-C7 Touch-Up Spray Gun - Amazon.com
Do you charge these with a compressor? ie are they reusable?
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Old 28-08-2013, 11:02   #44
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Re: Gel Coat Color Match

Quote:
Originally Posted by minaret View Post
Don't use cabosil, only virgin gel. I prefer Snow White to Pure White (it has a blue hue, but tint, shade, and hue are a bit advanced). Start too light and creep up on it, what you experienced is classic new guy stuff. Happens to everyone. Still happens to me on tricky colors. Patience is indeed key. I figure (for bids) two hours to match a shade of white, 4-6 for cool colors, 6-8 or more for warm colors. For a perfect match, that is, including a test spot.
Thanks for this, Minaret.

The first & only gelcoat repair job I described above involved small, narrow, but deep dings on the deck surface with underlying black laminate showing, mostly around the windlass & normal boarding/gateway areas, as one would expect. The cabosil was recommended by the gelcoat dealer to give the gel some structure I guess, or does it help seal? Do you nevertheless suggest just using gel alone with such small, deep, narrow dings? I did the grinding/Dremel thing first, btw, along with an acetone wipe before laying the gel/cabosil mixture on.

Re: the secret Mylar trick. Am I understanding the procedure right that the dry part of the Mylar square will be against the test patch, and the wet (spit) side against the old gel you're trying to match to?

Probably 'cause I'm such a noob at this, the dealer only sent me a small bottle of what looks like bright yellow for pigment (not labeled). This eventually turned out pretty close for the smooth parts of my deck surfaces, but the nonskid portions are more of a greyish color, although probably still considered 'off-white'. It didn't seem that the yellow was getting me there. Would a drop or two of black be needed do you think, as you suggested above? If at all possible, I'd like to keep my color inventory as simple as possible, esp. when it comes to the nonskid where I assume you can't really use compound or even wax as a follow-up. Or maybe I'm better off with a slightly different shade of the gel, as you also suggested?
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Old 28-08-2013, 11:07   #45
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Re: Gel Coat Color Match

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MEK is the hardener, yes??? I never found a source for the styrene monomer. I guess I should heve looked harder for it. Also, my gel coat sets up quickly and that is a problem with a sprayer. I am interesed in how you handle these situations. Since posting I did look for some youtube videos on get coat repair and sprayng but to date not much help.
Thanks

Hardener is methyl ethyl ketone peroxide, you reduce with methyl ethyl ketone. Totally different animals. Catalyze a small batch for each coat, each coat must be mixed differently anyhow. For really big repairs you can go as low as 1% on catalyst. Styrene monomer really increases flow, I like 5%/5%.
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