Heat Gun to Faded Plastic... Why Did This Work?

[Manhattan]

The rubber/plastic step on the bumper of my 2006 Land Cruiser faded to a light gray. I've tried a few chemical dressings - they'd last a few days. The guy who owns the shop that does the mechanical work on it, saw the bumper and said "Use a heat gun." Me: "Huh?" He grabbed a heat gun and did a 3" section. The plastic came back like new. I asked how long it'd stay like that. "Years. Like, as long as it took to get to that light gray."

When I got home, I did the whole strip - holding the gun about 3" from the surface, moving around slowly - making sure never to stop or slow too much. It was very cool. But, I can't figure out why it worked. Did it cook off the oxidized plastic? Surface level smoothing from the heat?

https://i.imgur.com/EeqlcBk.png

[Bruno Soares]

Heat brings the oils in the plastic up to the surface. It’s temporary and will eventually fade again. A new heat cycle will do it again until there are no oils left in the plastic.
IMO Solution Finish is the best way to restore plastic. And it will last a long time.

[Setec Astronomy]

Heat brings the oils in the plastic up to the surface. It’s temporary and will eventually fade again. A new heat cycle will do it again until there are no oils left in the plastic.
IMO Solution Finish is the best way to restore plastic. And it will last a long time.

There is no oil in plastic. "But it's made from petroleum!" If you bake a cake with eggs, I guarantee there is nothing you can do to that cake to make the eggs pop back out of it. Same with plastic.

I believe the answer to this question is that you are remelting the surface layer and "mixing" the oxidized surface with the substrate.

[itsgn]

The guy was wrong about how long that will last, because it will definitely not last the many years, that originally took for the plastic to fade. Also, this method only works a few times max, and every time you use it, you make the plastic even more brittle, than it already is, which in turn will increase the chances of it cracking and breaking. And of course the heat can damage parts near the plastic, so, in most cases (especially near non-painted parts) it's only safe if you remove the trim for the heat treatment.

You should possibly try Solution Finish instead, which does a great job at restoring the trim than regular water-based dressings and should generally last longer than the latter. Meguiar's Ultimate Black is also a nice compromise between restore effect and durability. And of course there are products like CarPro DLux and similar coatings that can last for a year or more (but might not be very good at restoring the color). You can also try to combine these (like applying Solution Finish to restore the color, then coat with DLux), but depending on how badly your trim is already damaged, the results and durability might vary.

[DBAILEY]

You are definitely making something fluid flow though. It may not be oils, but something is flowing. If you heat a spot too long you will see it flow and pool. You will end up with an obvious spot that looks glossier than the rest of the trim. I agree that every time you do this the plastic becomes more brittle and the trim does not hold onto dressings as well anymore.

However, some trim maybe so bad that a heat gun may be your best choice other than painting over it.

[Setec Astronomy]

You are definitely making something fluid flow though. It may not be oils, but something is flowing. If you heat a spot too long you will see it flow and pool.

Isn't that called melting?

[DBAILEY]

I guess to some extent. It doesn't look like melted plastic though. The fluid looks clear and raises to the top surface. The pebbled texture doesn't change. So something is melting/liquefying, just not the main structure of the plastic. I can see why it is thought of as oils, but I really don't have a clue what the liquid is. Plasticizers?

[Setec Astronomy]

Plasticizers?

Likely so. Perhaps the UV destroys the plasticizers at the surface, and if you can get very close to the melting point, you can get the plasticizers to migrate and get some back to the surface. Kind of like the way Dr. G said the UV inhibitors in clearcoat on plastic parts can migrate out into the substrate, which explains why those parts used to fade first, before they discovered putting the UV inhibitor into the plastic to prevent it from migrating out of the clear. That being said, perhaps it's a UV inhibitor that's coming to the surface, in the same way tires bloom.