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UV Damage


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UV won't affect the Carbon itself, but it sure can affect the Resin. Thus often a clear coat of Polyurathane with a UV stabalizer is coated over top. But even then, the clear coat can break down over time too and it needs to be maintained. Not using a clear coat usually results in the Epoxy yellowing from UV. I would not expect much in the way of reduction in strength of the spar as the Carbon should stop the UV from penetrating any further than the first layer.

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7 hours ago, wheels said:

UV won't affect the Carbon itself, but it sure can affect the Resin. Thus often a clear coat of Polyurathane with a UV stabalizer is coated over top. But even then, the clear coat can break down over time too and it needs to be maintained. Not using a clear coat usually results in the Epoxy yellowing from UV. I would not expect much in the way of reduction in strength of the spar as the Carbon should stop the UV from penetrating any further than the first layer.

Clear hates the sun,look at imported cars ,particularly the plastic bits ,seems to peel off nicely.

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8 hours ago, harrytom said:

Clear hates the sun,look at imported cars ,particularly the plastic bits ,seems to peel off nicely.

UV stabalizing additives are in themselves, not clear. Plus any material like Plastics and paints etc need two different forms of stabalizers to work in conjuction and offer the best protection. Usually one acts as a reflecter of UV and the other absorbs the energy of the UV Photon. Both work together well as a team, but each on it's own works very poorly. So there is this difficulty in producing a clarity of product vs great UV protection.
So mixing stabalizes into a clear coat has always been difficult while trying to maintain the clarity of the coat.
By the way, Black does not absorb UV, unlike all other bands of visible light and through into IR, which is absorbed by Black. So the most common UV stabalizing product in Black products is Carbon Black.

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Having watched this happen to my clear coated decks my conclusion is that the UV filter is not good enough to stop the epoxy below from breaking down. It only slows it down and eventually the bond between epoxy and clear coat gives up. The clear coat flakes off. Wait long enough and the wood below the epoxy laminate is affected enough for that bond to break. This never happens where I have paint on top of the epoxy.

Wood-epoxy cat. 35 years in Sweden so less UV than you have. https://www.reflectometrist.eu/

I am re-doing the clear coat on the decks this spring. I am scraping off the old stuff this weekend. Most of it comes off with little effort. Not so where it is in the shade.

This is the third time I do this, if memory serves.

Two-pot paint also breaks down but is a (much) slower process.

/Martin

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