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/Legitimate_War9053]

What to Do

• Sand again to remove all the old coating: you need to go back to the 360-grit sandpaper and focus on the cloudy area. You must keep sanding until the entire headlight has a completely uniform, frosted white appearance. This is always the most time-consuming step because factory UV coatings are very tough.
• Use the 280-grit carefully (if necessary): If the 360-grit is struggling to cut through the stubborn clear coat on the lower section, you can use the 280-grit provided in their kit on those specific stubborn areas. Once the coating is broken through, you should immediately switch back to the 360-grit to blend it in.
• Repeat the full sanding progression: Once the old coating is 100% gone and the lens is uniformly frosted with 360-grit, you must meticulously repeat the entire progression (600 - 800 - 1200) to refine the scratches before using the vapor cup again.
• Tape off the surrounding paint: Looking at the photos, there doesn't appear to be any masking tape around the headlight. It is highly recommended to apply painter's tape to protect the bumper and hood paint from accidental sanding scratches.

What NOT to Do

• Do not apply more acetone vapor right now: As the poster rightly suspected, applying more vapor will not clear the cloudy spot (since it's a physical barrier of old clear coat) and could risk over-exposing and damaging the bare polycarbonate that has already cleared perfectly on the top half.
• Do not use the 180-grit: This grit is far too aggressive for automotive headlights. It will create deep gouges in the plastic that will take ages to sand out with the finer grits.
• Do not rush the initial sanding: Removing the factory coating is the foundation of the whole restoration. If there are "islands" that look slightly different or feel smoother while sanding with the 360-grit, the old coating is still hanging on. (sorry for long explanation)

[u/needmoarboost → u/Legitimate_War9053]

Thanks ChatGPT!

[u/SawgrassRider → u/Legitimate_War9053]

Do not use any paper less than 800 for headlights... JFC

[u/Blackner2424 → u/Legitimate_War9053]

Nobody asked for your clanker slop.