XCR Fish eyes


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raymonddfz
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Hi,
I have been makeing a few carbon parts and the finish has been quite good for hand layup. I don’t use any gel coat before so  in order to add the UV protection, I have been coating them in XCR. However, no matter how much I rub them down, clean with a degreaser, the xcr always fish eyes. 

Any thoughts on what I can do to prevent it?
Hanaldo
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When you say 'degreaser', what exactly are you using? Products like engine degreasers are completely unsuitable for cleaning parts prior to coating. Needs to be a product intended for this purpose. 

Also, what grit are you sanding with? Epoxy needs quite a rough key to adhere well, I personally wouldn't go any finer than 180 grit.

I also wouldn't be using XCR resin for UV protection. It may be relatively UV resistant itself, but I highly doubt it has any UV blockers to prevent damage to the resin underneath. You really need a polyurethane topcoat for this.
Warren (Staff)
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120-180 grit is almost perfect for XCR.

Also if you are working above 23/24C the resin tends to get very thin very quickly which can effect its ability to grip and hence fisheye.  I have seen that as a problem with some of our customers using it in hotter climates.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
raymonddfz
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Hanaldo - 2/2/2021 4:26:41 AM
When you say 'degreaser', what exactly are you using? Products like engine degreasers are completely unsuitable for cleaning parts prior to coating. Needs to be a product intended for this purpose. 

Also, what grit are you sanding with? Epoxy needs quite a rough key to adhere well, I personally wouldn't go any finer than 180 grit.

I also wouldn't be using XCR resin for UV protection. It may be relatively UV resistant itself, but I highly doubt it has any UV blockers to prevent damage to the resin underneath. You really need a polyurethane topcoat for this.

I thought XCR was ideal for UV protection. That is why I have been using it... a little confused

Warren (Staff)
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XCR has a high level of UV resistance but is not 100% UV stable so over time it will still eventually yellow just much slower than a "typical" epoxy resin.  A UV stable lacquer is generally the best solution for the ultimate UV protection.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
Hanaldo
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There is also a difference between being UV resistant, and having UV blockers. A UV resistant coating will resist yellowing and degradation of itself, but it doesn't prevent the UV from passing straight through to whatever is underneath.

You can witness this with unpainted Kevlar laminates, as Kevlar is also highly UV sensitive. After a few months in the sun, Kevlar will start to turn brown. This isn't the epoxy yellowing, it is the UV passing through the epoxy and degrading the Kevlar. To protect it, you need to prevent the UV getting to it, which is why Kevlar laminates are very often painted with a solid colour. 

But the automotive and marine industries have been dealing with this for years, which is why automotive and marine 2k coatings tend to have the best UV blockers. And even within those industries, some products are much better than others. House of Kolor Show Klear is the absolute best I have found. Ive got a couple of test pieces that have been coated and sat outside in the Aussie sun for the last 2 years with still not a sign of yellowing. Other coatings and uncoated parts won't last a month of constant exposure to our summer sun without showing signs of degradation, so it is very impressive.
raymonddfz
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Hanaldo - 2/5/2021 3:51:45 PM
There is also a difference between being UV resistant, and having UV blockers. A UV resistant coating will resist yellowing and degradation of itself, but it doesn't prevent the UV from passing straight through to whatever is underneath.

You can witness this with unpainted Kevlar laminates, as Kevlar is also highly UV sensitive. After a few months in the sun, Kevlar will start to turn brown. This isn't the epoxy yellowing, it is the UV passing through the epoxy and degrading the Kevlar. To protect it, you need to prevent the UV getting to it, which is why Kevlar laminates are very often painted with a solid colour. 

But the automotive and marine industries have been dealing with this for years, which is why automotive and marine 2k coatings tend to have the best UV blockers. And even within those industries, some products are much better than others. House of Kolor Show Klear is the absolute best I have found. Ive got a couple of test pieces that have been coated and sat outside in the Aussie sun for the last 2 years with still not a sign of yellowing. Other coatings and uncoated parts won't last a month of constant exposure to our summer sun without showing signs of degradation, so it is very impressive.

Thanks for the info, so for future reference, rub down carbon part with 120-180 grit, coat with XCR at a temperature below 23deg and then a coat of automotive 2K lacquer.  I ask why bother with the XCR and will all this help my original issue of fish eyes? The degreaser I used by the way was an automotive panel wipe. 


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