Headlight restoration 50/50.

[Part-timer]

If you're going to use mineral spirits, be aware that there are 2 flavors; mineral spirits (paint thinner) and oderless mineral spirits. The difference between the 2 is that odorles mineral spirits are distilled multiple times to remove odor causing solvents so it is much purer than regular MS or paint thinner. It may not matter, but when you're restoring headlights for profit and giving a 2 year guarantee, you don't want to take any chances since the difference in cost would be pennies per headlight. We no longer use MS for cleaning, we use alcohol which attracts moisture and dries in seconds.

ray6

I always use the exact odoress type/brand stated in the beginning of this thread.

 

[Part-timer]

There's not too much difference in the polycarbonate itself, except for extreme curves or thickness the mix might be slightly different.

The main differences you will see are due to:

The protective coating formulas, primer vs. no primer, how it's applied (dipped, sprayed, electrostatic etc.,) how it's cured (heat vs. UV), number of coats, etc. All manufacturers apply at least the minimum to pass ANSI tests, but some apply additional material for wearability and abrasion resistance (like Jeep, so bushes don't scratch the headlight).

UV protection is limited because you can only add so much UV absorption material to the carrier. Additional material will not cross-link. This is why some headlights have tough coatings but they are still yellow or cloudy.

The last variable is UV exposure: where you live, where you park, and the shape of the headlight. PT cruisers will always fail sooner than others because the lamp surface is almost horizontal so it gets maximum exposure during the day. Another car parked right next to it (like an older Chevy pickup) with vertical headlights will last much longer because UV exposure is far less.

ray6

The only reason I asked about this is because some headlights, after removing the oem coating, it seems harder to remove some deeper scratches....compared to other lenses. Maybe its just because the harder coating takes harder force to remove, thus causing deeper grooves in the lens itself.

 

[snellvilleauto]

How do you guys prevent water spotting on this freshly Spar coating? My spot after the first rain and it was so bad i had to redo the whole thing over just to get rid of the water spotting

 

[ray6]

If in fact you really have removed the old coating, you're dealing with the natural hardness of the polycarbonate which varies from manufacturer to manufacturer. If you are wet sanding, and the runoff is milky color, you're down to the polycarbonate base.

ray6

 

[Part-timer]

How do you guys prevent water spotting on this freshly Spar coating? My spot after the first rain and it was so bad i had to redo the whole thing over just to get rid of the water spotting

They shouldn't spot if the spar has cured properly. How long do you allow for them to cure?

 

[Part-timer]

There's not too much difference in the polycarbonate itself, except for extreme curves or thickness the mix might be slightly different.

The main differences you will see are due to:

The protective coating formulas, primer vs. no primer, how it's applied (dipped, sprayed, electrostatic etc.,) how it's cured (heat vs. UV), number of coats, etc. All manufacturers apply at least the minimum to pass ANSI tests, but some apply additional material for wearability and abrasion resistance (like Jeep, so bushes don't scratch the headlight).

UV protection is limited because you can only add so much UV absorption material to the carrier. Additional material will not cross-link. This is why some headlights have tough coatings but they are still yellow or cloudy.

The last variable is UV exposure: where you live, where you park, and the shape of the headlight. PT cruisers will always fail sooner than others because the lamp surface is almost horizontal so it gets maximum exposure during the day. Another car parked right next to it (like an older Chevy pickup) with vertical headlights will last much longer because UV exposure is far less.

ray6

ray6......in the last post you sent me you said, "If in fact you really have removed the old coating, you're dealing with the natural hardness of the polycarbonate which varies from manufacturer to manufacturer"

but in the post above you say, "There's not too much difference in the polycarbonate itself, except for extreme curves or thickness the mix might be slightly different."

Which one is it?

 

[ray6]

Iagree it was confusing. I talked to my plastics friend and he informed me that there are some coatings and compounds used in molding polycarbonate that enhance scratch resistance and are similar to the stuff they use on eyeglasses.

He said they don't play part in UV protection and could be just on the surface or part of the polycarbonate and difficult to remove.

He thought that once you see milky white residue you are probably down to the polycarbonate.

ray6

 

[ray6]

If you've ever wondered what's happening to headlights when being restored, you might find this interesting.

Photos are in an album titles: Headlight surface

The way most UV protection works is that certain wavelengths of light (specifically UV) will cause certain molecules to adsorb the light, converting it into heat. Over time, these molecules become so agitated that they break their bond with nieghboring molecules. This effects the orderly arrangement of the molecules and they turn opaque/yellow.

Depending on the breakage, some of these molecules are easy to remove by using a solvent or by abrasion. Undamaged molecules and cross links are harder to remove. Also, the actual composition, thickness and previous UV exposure cause wide variations in headlights.

More horizontal headlights such as PT cruisers receive more UV than vertical ones.
Enclosed is some microphotos of an actual headlight going through our older restoration process.

This is what the deteriorated factory coat looks like. You can see the breaks. If you could see it sideways, it would look like shallow canyons.

This is after the first pass of stripper. The minor fissures are removed, and additional passes will remove the deeper fissures.

500 GRIT sanding marks
1500 GRIT
2500 GRIT
COATED - Coated with polyurethane- notice how it fills in the sanding marks.
COATED 2K- requires finishing to 3000 before applying
PRE-STRIP- Headlight surface before restoring
1ST STRIP- First application of stripper

eay6

 

[snellvilleauto]

They shouldn't spot if the spar has cured properly. How long do you allow for them to cure?

I let it cure over night inside the garage (at least 12 hours). I now put a few coats of sealants on them. We'll see what will happen the next rain. What do you suggest i should do?

 

[slammin86]

Would 2500 grit be fine enough to put this over? I want to try this on the camry headlights but do not have any 3000 grit.

 

[Part-timer]

I let it cure over night inside the garage (at least 12 hours). I now put a few coats of sealants on them. We'll see what will happen the next rain. What do you suggest i should do?

I don't know what to tell you. I live in Daytona Beach Florida and only let them cure about an hour or two before the owners usually want to drive them home. I've never had any problems like you describe.

 

[Part-timer]

Would 2500 grit be fine enough to put this over? I want to try this on the camry headlights but do not have any 3000 grit.

Try it and let us all know.....lol (just kiddin') I've heard people on here only sanding them to 1500 and then coating them. I think to some extent, it's individual preference. I imagine 2500 would be fine. I personally take them to 3000 though.