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Old 01-04-2017, 03:46 PM   #1
Duffsfromks

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Default Top coat issue

I was provided a top coat, however I ordered it over the phone and there must have been confusion with my request. I'm making body panels and exterior parts out of cf. I of course am desiring the part to have that deep wet gloss look. The top coat I got is for interior, like bar tops, and just doesn't get super solid or protect from uv. I'm in a time crunch, could I possibly just build a barrier around the part and pour epoxy into the dam then sand and buff and result in a similar effect? Otherwise this top coat is going to take about 5-7 typical shipping wait, I don't have that luxury. Any help or advice would be greatly accepted. Thank you composites community.
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Old 01-31-2017, 05:40 PM   #2
fasta

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Epoxy don't have any UV either. Probably worse than an interior paint or varnish.

Lately I have been using the Duratec sunsheild like a clear primer just to get the surface rubbed back nice and then I coat that with any other two part clear.
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Old 04-27-2017, 11:20 AM   #3
Zebra

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If you make the part using polyester resin or vinylester resin instead of epoxy, you can use a clear gel coat layer in the mold before adding the cf.

For cf parts made with epoxy resin, I have been using a spray-on clearcoat and it works fairly well. I sand the surface first going from 400 to 2000 sander paper.

I have never been able to make epoxy bartop work well on anything except a perfectly flat tabletop. Even then, I struggle with fisheye issues. For dimensional parts, the epoxy bartop just runs off and dries with gaps everywhere for the bit that stays on.

The only way I have had any luck with epoxy bartop is by letting it set to a thick gel before applying it. The trick is to use it when it is thick and sticky enough to stay on your part but stick loose enough to self level to a relatively smooth surface. I still have to sand and polish the end result though.

I find an automotive spay on clear coat to be much quicker and easier if the part surface is properly prepped first.

I potentially have a few other ideas for you, depending on the shape of the part / mold. Can you post a pic of the mold?
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Old 04-30-2017, 05:23 PM   #4
fasta

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Epoxy resins are typically going to run away, especially on a mould with a release coated surface. Most guys using an in mould coating will do this with a sprayed two part clear paint or resin like Duratec Sunshield. Either is built up starting with mist coats and then heavier coats until well covered.

For people coating an actual bar top there are specific coating resins for this like west 105/207 and many others too.
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Old 05-04-2017, 01:51 PM   #5
Zebra

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I actually found an epoxy based clear gel coat for use on carbon fiber epoxy parts recently but it was only available in the UK from Easy Composites. Just my luck...

We know that gloss coatings on carbon fiber / epoxy parts should come from the mold but it sure would be nice to have an effective clean epoxy based gel coat as an option for surface repairs for when parts don't come out perfect.

I would love to be able to reduce wastage by not having to throw away parts with one or two flaws.

Sanding and adding a spray on clear coat is the next best thing I guess.

Btw, I sometimes use an epoxy resin with UV protection already included. These are the ones that are usually slightly blue in color from the "optical brighteners" they add. It certainly seems like it would less likely to yellow than my resins that use an orange / yellow hardener like the one from Composite Envisions.
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Old 05-04-2017, 06:20 PM   #6
Hanaldo

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Quote:
Originally Posted by Zebra View Post
I actually found an epoxy based clear gel coat for use on carbon fiber epoxy parts recently but it was only available in the UK from Easy Composites. Just my luck...

We know that gloss coatings on carbon fiber / epoxy parts should come from the mold but it sure would be nice to have an effective clean epoxy based gel coat as an option for surface repairs for when parts don't come out perfect.

I would love to be able to reduce wastage by not having to throw away parts with one or two flaws.

Sanding and adding a spray on clear coat is the next best thing I guess.

Btw, I sometimes use an epoxy resin with UV protection already included. These are the ones that are usually slightly blue in color from the "optical brighteners" they add. It certainly seems like it would less likely to yellow than my resins that use an orange / yellow hardener like the one from Composite Envisions.
So far as I know, Easy Composites don't have a clear epoxy based gelcoat. They have GC50, but that is an epoxy compatible polyester based gelcoat.


Honestly, I wouldn't trust any epoxies that claim to be UV stable. I know some of them have UV absorbers or stabilisers added to them, and these do help, but in my experience they ALL yellow.

If you have a part that is going to be exposed to consistent UV (ie, an external vehicle panel on a daily driven vehicle), then the only reliable coating would be a 2k polyurethane. I even have my suspicions that Duratec Sunshield will yellow to some degree, but I've got 5 year old parts that aren't showing any signs of it yet. Only reason I am suspicious is I have top-coated some white panels, and these have significantly yellowed since I sprayed them 3 years ago. So perhaps the carbon hides it well enough. But again, if you have parts that absolutely can not yellow - 2k polyurethane all the way.
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