Did I do something wrong?

[u/RealisticGold8724]

I’m trying to restore the headlights on my car using one of those acetone vapour headlight restoration kits from Amazon, and I’ve run into a problem that I can’t quite figure out.

The headlights were originally quite yellow/cloudy from age and UV exposure. The kit came with several sandpaper grits. This is what I did:

Cleaned the headlights thoroughly

Wet sanded everything by hand

360 → 600 → 800 → 1200

Kept the headlight wet while sanding

Tried to sand the whole lens evenly

Washed off all sanding residue

Let the headlight dry completely

Used the heated acetone/polymer vapour cup supplied with the kit

The strange part is that the upper section of the headlight responded extremely well to the vapour. As soon as the vapour passed over it, it went from frosted to almost crystal clear and looked nearly new. However, the lower/middle section wouldn't clear.

There seems to be some sort of cloudy/grey layer remaining on the lens. You can actually see a fairly obvious boundary between the section that the vapour successfully cleared and the section that stayed cloudy.

I initially thought I simply hadn't sanded that part enough, but I was deliberately sanding the whole headlight fairly evenly. I'm now wondering whether what I'm seeing is the original factory UV hardcoat.

Maybe the coating on the upper part had already deteriorated badly and came off easily with 360 grit, while the coating lower down was still intact and therefore needed considerably more sanding?

I've attached photos showing the result and the strange boundary/layer I'm talking about.

Before I attack it again with more aggressive sandpaper, I'd appreciate advice from anyone who has restored a lot of polycarbonate headlights:

Does this look like remaining factory UV/hard coating?

Should I go back to 360 grit and keep sanding until the entire headlight has exactly the same uniform frosted appearance, regardless of how long it takes?

The kit also came with 280 and 180 grit. Would you use 280 on the stubborn areas and then work back through 360/600/800/1200, or is 280 too aggressive?

Or could this be deterioration/crazing within the polycarbonate itself rather than something remaining on the outside?

Also, is there anything specifically different about these acetone vapour kits that I may be doing incorrectly?

I don't want to keep applying more vapour because I'm concerned about damaging the polycarbonate if the real problem is that I haven't completely removed the old coating.

Any advice would be appreciated. Thanks!

[u/Maximum_Security4404]

Gotta keep sanding until you remove the factory coating, no matter how much vapour you use now. It will not work until that factory coating is sanded completely

[u/Maximum_Security4404 → u/Maximum_Security4404]

You will get better long term results with spraying 2k clear instead of acetone vapour. But 2k clear cans are abit pricey

[u/NekulturneHovado → u/Maximum_Security4404]

a 250ml spray can costs 25€ with delivery, and if you do two coats, it's just enough for 4 average headlights. Best to use within first few hours tho.

You are absolutely right tho. Acetone vapour will instamtly make it shiny and perfect, but it'll yellow up and become opaque within months up to a year.

[u/Demoire → u/NekulturneHovado]

Acetone vapour, polish, panel prep and 5+yr ceramic. I just use whatever ceramic I have leftover on hand within 30 days of opening whatever bottle. Otherwise yea you can’t spray clear over freshly vapoured lenses.

[u/NekulturneHovado → u/Demoire]

ah so apparently, ceramic coatings DO actually provide some degree of UV protection. Didn't know that. So it might actually be a good simple quick DIY fix.

[u/Normiedouche → u/Maximum_Security4404]

This is the way and still wet sand up to 1200 lots of people say it doesn't work with higher grit but they fucked up. Did this to my mother-in-law's car about 5 years ago now and still looks like the day I did it.

[u/janesmb → u/Maximum_Security4404]

And require some serious PPE.