Correcting a yellowing clear coat?

[PHArchivist]

What can be done? Anything?

In my experience, nothing really... But I've never aggressively pursued this either - more or less have just "lived with it" when clear coats have yellowed.

Here's the situation:

I've used a moderately extensive amount of Testor's Dull Coat on a very important project. Too late in the game, I confirmed my suspicions (fears) by shooting a test coat on clean white styrene. The clear coat went on in a very light honey shade, and has progressivly darkened.

Worse, it has turned the nice, light bleu/grey of my project into a dirty yellowish-beige/grey.

So...

What exactly goes on when a clear coat yellows?

Will the yellowing agent (whatever it is within the composition of the paint that turns yellow) fade over time, reverting to a more true clear?

ANy thoughts about wet-sanding at about 2,000 grit - fine enough to perhaps take off a micro-layer of clear without effecting the finish underneath?

Any more thoughts?

 

[KevVader]

Wetsanding or polishing in stages with decreasing abrasives is the only way to get rid of yellowing clear as you are grinding down the discoloured material. I have some carbon fiber bits on my bike that I'm restoring as the clear on them has yellowed. Increased exposure to UV or excessive heat will cause the yellowing.

And yes the yellowing will reappear in time if the same levels of UV and/or heat are present unless you use a clear with inhibitors or constantly wax with UV protective wax...i.e. any high quality car wax...preferably polymer based.

 

[PHArchivist]

Thanks Kev...

 

[PHArchivist]

A foreseeable problem with wet-sanding is consistency.

The surface area I am dealing with is large, and removing an even amount all the way across would be difficult.

 

[KevVader]

Thn buffing with decreasing abrasives polishes at each stage is your best bet...especially if you use a power orbital polisher like a Porter Cable 7424. It's the only way to reasonably guarantee consistent and even polishing on a large surface.

 

[PHArchivist]

Thanks again...

What about the effects of time? Has anyone paid close attention to this>

I know (from more years in this hobby than is healty) that time is the enemy of a clear coat, at least in the short to mid term.

But what about long term? Ten years, plus...?

-Does the yellowing just get worse?
-Will it stabilize and remain the same?
-Might the yellowing itself begin to degrade back to a more true clear?

I have an old 1:4 scale Screamin' Stormtropper that I clear-coated wth Testor's about 10-15 years ago. I'll have to pull it off the shelf and take a close look at it.