How low of a grit sandpaper have you used on a headlight restoration?

[KJW Detailing]

Good Evening Autogeeks,

I was working on a friends headlights this afternoon. She had told me, she had done several things prior to calling me (OTC products and toothpaste) and thought the issue was inside the headlights.

After finishing, I was unsatisfied with the results. I went as low as 600 grit sandpaper and I'm wondering if I should/could have gone lower? Work the 600 grit sandpaper longer?

What could I have done differently?

Thanks!

[Setec Astronomy]

That old coating is tough to get off, I'm pretty sure I went down to 400 or 320 on the set I did. Working the 600 longer is not the way to go, you shouldn't have to work any grit longer than the other. If the grit you are using isn't cutting it (no pun intended), you need to drop lower. But the lower you go the more steps you will need on the way up to take out the heavy-grit scratches.

[KJW Detailing]

That old coating is tough to get off, I'm pretty sure I went down to 400 or 320 on the set I did. Working the 600 longer is not the way to go, you shouldn't have to work any grit longer than the other. If the grit you are using isn't cutting it (no pun intended), you need to drop lower. But the lower you go the more steps you will need on the way up to take out the heavy-grit scratches.

That's what I assumed. Thanks Setec Astronomy.

[ray6]

It looks like all of the original factory coating was not removed. As to choosing which grit to start with, that's a difficult question to answer.

The rougher the grit, the faster the removal, but the more sanding damage, the longer the repair.

Think of it this way:
Your first sanding step removes the factory coating. All additional steps are only to repair the sanding damage from the first step.

Further complicating matters is that your final grit has much to do with your final coat. Some coatings require a finer finish than others.

I don't think choosing 600 was the problem, I think you didn't sand long enough with 600 to get the old coating off. One clue I often use is to watch the color of the sanding aid. Polycarbonate residue is white. When the liquid turns milky, it means you are down to the polycarbonate.

Many times with BMWs and Jeeps I start by scraping with a razor blade, followed by 500 grit, then 1500, then either coated with solvent based or sand with 3000 then coat with water based.

Theoretically you could sand off the old finish entirely with 3000 grit, but it would take weeks.
Hope I'm not confusing you.
ray6

[oldmodman]

The roughest grit I have used is 320.

And that was on an absolutely opaque lens on an older car. I was a dark yellow color and very rough feeling.

I sanded with it until the dust coming off was white again. Then used 600, 1500, 3000 and then Spar varnish. Came out looking like new.

[reggie1967]

The roughest grit I have used is 320.

And that was on an absolutely opaque lens on an older car. I was a dark yellow color and very rough feeling.

I sanded with it until the dust coming off was white again. Then used 600, 1500, 3000 and then Spar varnish. Came out looking like new.

the lowest i used is 180/220 just to skim off the ruff edge then 320 up to 2000/3000

[master detailer]

400 then 800 to 1000 comp

[ksigna]

What pads and polish are you guys using?

[ray6]

Good Evening Autogeeks,

I was working on a friends headlights this afternoon. She had told me, she had done several things prior to calling me (OTC products and toothpaste) and thought the issue was inside the headlights.

After finishing, I was unsatisfied with the results. I went as low as 600 grit sandpaper and I'm wondering if I should/could have gone lower? Work the 600 grit sandpaper longer?

What could I have done differently?

Thanks!

It looks to me that all of the original coating was not removed. There's two parts to the equation; selection of grit and sanding duration. Many times with BMWs and many SUVs or some Chevys I start with a razor blade. This may seem harsh, but actually works well for me. After the blade I will use a stripper and/or sand with 500 grit.

Technically, you could start with 80 grit, which would quickly remove the old coating, but would also require a lot of sanding disks or paper because it would fill up quickly with the old coating. Then, because of the amount of surface damage you would need to spend a lot of time removing the deep sanding scratches from the 80 grit.

The reason I use a razor blade on some headlights is because it is faster and cheaper than sandpaper. The razor blade doesn't clog up, but will go dull. But at 10 cents apiece, who cares? It also clears easily with 500 grit.

At the other extreme, you could start out with 2000 grit which would also remove the coating, but very very slowly. So, it's a question of selecting the right grit to begin with. It will vary with each headlight.

One suggestion I would propose is regardless of what grit you start with, wet sand with a good lubricant and watch the color of the sanding aid. If it's slightly yellow, it's old coating. If it's white, it's polycarbonate (headlight base). Once it turns white, you have removed the old coating and now your job is to repair the sanding damage.

Another suggestion is to sand/compound until the headlight looks like new or as good as you expect. It is true that some coatings will hide your sins by filling in shallow sanding scratches, it's also true that if the headlight looks great before the coating, it will look even better when coated.

I went through the same scenario early on with BMWs and Jeeps. I wasn't removing all the old coating. I think if you redid the headlights and watch the sanding aid or water/soap if you don't have sanding aid color and sand until all the old coating (and your newly applied coating) you'll get much better results.

P.S.- If you used spar/MS for the final coat, remove it with MS as soon as possible. It fully cures in about 14 days and the sooner you remove it, the better. Hope this helps.
ray6

[oldmodman]

What pads and polish are you guys using?

I don't even bother with polishing after the 3000 grit sanding disc.

The final 'tooth" after sanding just give the spar varnish a place to "bite" And I cannot detect any difference in final clarity after the spar varnish has fully dried between a lens that had the 3000 grit sanding as the last step and a lens that was polished as the last step. And several people have posted that they are no longer going to an ultra fine sandpaper before coating with spar. They are stopping after 2000 grit.