Clearing over clear plastic

jlcustomz

jlcustomz

evil painter
A few future projects could involve clearing over acrylic( plexiglass) or polycarbonate (lexan). Figured I'd ask here rather than learn the hard way as usual & I know others would have interest in this subject.

One would be sanding & clearing over worn headlights. I'm sure results on this one hinge partly on condition of head lights. I know some tint the mix slightly.
Another would be custom making tail light & marker lenses to fit snug to their cutout hole & sand flush with vehicle contour to appear smooth with body after clear.
Next is a set of custom lexan quarter windows (non operating) which scratch too easy & are hard to make scratch free.

What might be a minimum & maximum sanding grit before clearing. 400 to 1000?
For a custom flush marker fitting through the metal, wondering about filling any small gaps between plastic & body. Any certain clear filler products or spray a few coats of clear & sand before spraying rest of area.
Would spraying a lexan or acrylic quarter window give a better overall appearance next to real glass than the easy to scratch & hard to buff plastics? Window is black tinted on inside by the way.. Universal clear or something harder?
Thanks in advance, Joe.
 
for headlights use 600-800 grit. any higher than 800 and you can have flaking issues. and lower than 600 and it will get more hazy. most scratch resistant way your gonna go for windows is plain polycarb. clearing over it wont help avoid that. polycarb will be more scratch resistant than universal clear. as for clear filler, are you looking to make the lenses completely seamless and clearcoated over or just a very small hairline seam?
 
The most important thing to know is that polycarbonate lights have a scratch and UV resistant coating applied to them that must be removed completely before clearing. Urethane clear must be applied to "virgin" polycarbonate for maximum clarity and adhesion. Usually the best way to do this is to begin sanding to remove the coating with something fairly aggressive like 500 or 600 DA (even 320 for badly degraded or chipped lenses), then refine out with wet or dry paper. I don't normally ever contradict such an accomplished forum member as Jim C, but once this coating is completely removed, adhesion has not been an issue for us even when we have refined our scratches out to 2000. The solvents in the clear partially melt the polycarbonate, and there is apparently some diffusion of the urethane into the polycarbonate and vise-versa. We've experimented with various grits over the years and have settled on 1000-1200 as being the best compromise between speed and appearance. I say this with a pretty high degree of confidence as the chip-seal on the roads here is composed of very sharp rocks, and front ends here see a LOT of abuse.
 
Good info there . On headlights I first polished a bunch for people back when things were slow around 08' or so. At that time the layer of uv coating wasn't common knowledge like it is now & the first thing I learned the hard way is all that pretty sanding & buffing work didn't stay clear for long. Haven't tried one out yet, but those spraymax 2k clear aerosol cans seem like they could be a good idea for someone doing mobile headlight restoration. I was pretty sure that urethane clear would actually melt into some plastics.

On polycarb windows,​ guess I need to to refine my methods to get it back to crystal clear after sanding out a scratch or chip, hadn't spent the time to do so yet.

On the marker / tail light​ flushing I would like to shoot for at least a very small hairline seam. With the fabrication process involved on a custom sword blade shaped tail light idea on the rounded rear corners of a truck, absolute perfect fabrication of fit between the metal cutout & the plastic insert with a 2 dimensional level to fit & stop against the hole is next to impossible.
 
crash, are you putting tinted clearcoat right over the polycarb lenses or are you using a tinted intercoat? using any adpro?
 
No intercoat, no adpro, just urethane clear! We do not do tinted lenses, but if we were to, I would probably want to try a compatible pre-activated black SS in the clear. Getting the ratio right might be a challenge!

Adpro has not produced good results for us, it causes a greater loss of clarity, and Lexan is not one of the plastics that requires it, anyway.
 
My name is William what clear.can i use without the adhesive a promoter that will give long durability to headlight
 
As stated by crashtech, most important step is removing whats left of the factory coating sanding down to the raw plastic, then any good quality urethane clear can be used without promoter, as it will partially melt into the plastic.
 
The finish on the headlights in the picture. Have they been buffed or off the gun and if you had to buff what would be your advice thank you.
 
If you're referring to the pic in my signature, those were handmade light housings made from 1/2" thick lexan, as is.
As I stated earlier, the cruel lesson I learned years ago on polishing headlights has to do with this protective coating that has to be removed to coat them with clear. Once you remove this coating by sanding & buffing or even just a heavy buffing , the plastic fades continually from sunlight exposure. My work truck that gets fla sun daily needs a quick repolishing about once a month to look even half decent at the age they are. now ( 2001). So called wipe on protective coatings don't do much either. If I can squeeze it in between painting projects at work, I'll remove the lights & resand in stages & spray with some euro clear I got laying around.

So my advice is to go with crashtech's advice in post 3 ... sand in stages, wipe with alcohol based cleaner & spray with clear.
 
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