Polishing Plastic Bumpers

Z

ZeroDfx

Member
I am curious as to how others machine polish their plastic bumpers so that they buff out to a bright gloss to match the gloss achieved on the paint.



I find myself fearful of being too aggressive with either the pad or the polish on my PC7424 for fear of making the bumper duller instead of brighter by scratching the surface. The bumpers on my 2000 BMW 5 series clearly need polishing after claying to remove accumulated embedded road grime; can I use an orange pad with something like Optimum II or Meguiar's Ultimate Compound without fear of scratching the bumper?



Regardless, what combination would you recommend? And how would you suggest going about cleaning up this area of the car?

Many thanks.
 
I would avoid being that aggressive right off the bat. In theory the bumper should buff out the same, but I find the paint to often be softer, thus more heavily damaged. It is important to accept that perfection may not be attainable. The other problem is the various angles and edges that make them so easy to do more damage than good. I usually start with a LC white pad and a medium/medium-aggressive polish like Meg's 205 or Menzerna Power Finish. It can be very time consuming, so be patient. If that isn't enough, then I step up to the orange pad, but stick with the same polish. I really try to avoid being more aggressive than that unless the paint is unusually stubborn.



What color is your Bimmer?
 
Some areas you have no choice but to do by hand if you want them corrected. Otherwise, on the softest of soft, the bumpers tend to be a little harder, but on the hardest of hard, the bumpers a little softer.



What you will find is polishing by machine, whether DA or rotary, because of the smaller diameter pads, a less aggressive combo will reap faster benefits than expected on a pad of larger size. So just keep this in mind when combining all the help you get in this thread.
 
Also keep in mind that plastic bumpers are painted separate from the car and with different paint. Rarely do they look exactly the same as the rest of the car, and they often respond differently to polishing too.
 
How can you tell if you have a plastic bumper? Just hit it? Because my Urethane bumper and a plastic bumper acted about the same when hit. Also should this be something you really worry about?
 
You can save yourself a lot of work if you use something like FK 215, as it has petro based cleaners in it and will remove that embedded road grime without being abrasive to the flex agent paints used, also known as elastimeric paint.

Very porus, has to be as the parts are made to "bend slightly", so the paint has to have more flexibility.

I think is you use the 215 or someother similar product, you will observe a remarkable difference.

Grumpy
 
Urethane/plastic, no big difference, they are much the same.

Key thing is that they are finished with a flex agent additive in the paint.

Also known as an elastimeric additive.

Very porus-IE-soft.

DO NOT CREATE HEAT WHEN BUFFING THESE PARTS!!!!!

Grumpy
 
Rei86 said:
How can you tell if you have a plastic bumper? Just hit it? Because my Urethane bumper and a plastic bumper acted about the same when hit. Also should this be something you really worry about?
Click to expand...



They will act similar, what you will find is plastics will sometimes warm up a little faster to friction simply because a giant steel panel for example will absorb and dissipate heat better than plastics would. One of your concerns(you should not be scared) is that bearing down on a plastic panel will certainly heat up fast - even with the docile DA and a small pad. So with this you should only be concerned about not going crazy as far as pressure on the plastic components, and realize that with a DA they will take a little longer to cool down in the event you warm them up, if only slightly.



The only other prominent issue assuming you are familiar with machine polishing is that on non OEM repaints(and some OEM paints), you need to just be aware some poor paint jobs have twisting and delamination issues. This would more than likely become an issue IF you chose to work on the area like a maniac, using tons of pressure, disregarding any warmth or heat and other wise working with complete ignorance.
 
I have a somewhat related question for you Ron. I came across a weird paint issue last weekend. Car was an '80 Vette, Claret Red, single stage, also a repaint some time back. Other than having swirls and RIDS, paint looked good. I was polishing with M105/Surbuf with great results....however, once I started hitting the bumpers, everything I tried dulled the paint big time. After trying about 6 different polishes, various pads, rotary, DA and hand, I began to be concerned. Eventually one of my polishes, Sonax Paint Cleaner improved the finish, which at least got me back to where it was prior to polishing. The paint was definitely a lot softer then the rest of the paint. I could actually sink a finger nail into it with moderate pressure. Very weird! After some time with the Sonax we were able to get it looking good, but I have no idea what caused this issue.



Here is a pic of what the bumper looked like prior to polishing.

7a96ed98.jpg




And here was after several other polishes. (M105, D300, M205, M83, M80, and even M07 to see if it helped).

efedb085.jpg






Thoughts?





Sent from my iPhone using Tapatalk
 
When refinishing is done of these parts, the painter has to add the flex agent to the paint.

The flex agent, depending on the supplier of the paint, usually requires a different solvent for reducing, often painter assume they are smarter than the one who made the paint, and cheap, so they use their normal solvent, IE, the "cloudiness".

As far as the added flex agent, he added too much so the paint ends up being very soft and porus.

As I said on another post, "hard to polish a sponge".

Grumpy
 
Ron Ketcham said:
When refinishing is done of these parts, the painter has to add the flex agent to the paint.

The flex agent, depending on the supplier of the paint, usually requires a different solvent for reducing, often painter assume they are smarter than the one who made the paint, and cheap, so they use their normal solvent, IE, the "cloudiness".

As far as the added flex agent, he added too much so the paint ends up being very soft and porus.

As I said on another post, "hard to polish a sponge".

Grumpy
Click to expand...



That makes sense, thanks! I also noticed that after washing it that the water or soap temporarily stained the paint on the bumpers. I actually thought I'd have to re-polish but it went away after a few minutes.





Rasky
 
RaskyR1 said:
Also keep in mind that plastic bumpers are painted separate from the car and with different paint. Rarely do they look exactly the same as the rest of the car, and they often respond differently to polishing too.
Click to expand...



Exactly. Nothing like doing a car with rock hard clear and having a pleasant surprise when getting to the bumpers!



Ron - I agree with your assessment of Rasky's question. I'm finding more and more shops that are using paint lines that don't require flex additives in their paint formulations for platic parts? Shops claim that many of the manufacturers are using more naturally flexible paint these days. On the other hand, I know a large dealer chain (Auto Nation) that has an exclusive contract with Dupont(Finish Master) and they add flex to almost everything? As Appraisers we are instructed to leave these add ons off our initial estimate until a shop requests them per their SOP.
 
autoaesthetica said:
They will act similar, what you will find is plastics will sometimes warm up a little faster to friction simply because a giant steel panel for example will absorb and dissipate heat better than plastics would. One of your concerns(you should not be scared) is that bearing down on a plastic panel will certainly heat up fast - even with the docile DA and a small pad. So with this you should only be concerned about not going crazy as far as pressure on the plastic components, and realize that with a DA they will take a little longer to cool down in the event you warm them up, if only slightly.



The only other prominent issue assuming you are familiar with machine polishing is that on non OEM repaints(and some OEM paints), you need to just be aware some poor paint jobs have twisting and delamination issues. This would more than likely become an issue IF you chose to work on the area like a maniac, using tons of pressure, disregarding any warmth or heat and other wise working with complete ignorance.
Click to expand...



I learned the hard way to verify the material under the paint before polishing it. I melted a small spot on the plastic strip on the back of a Land Rover just below the back window. It is painted the same as the rest of the body and since it is a very straight piece I assumed it was metal and got too aggressive trying to remove a scratch. The spot is relatively hidden by the rear wiper and the owner was pretty cool about it.
 
That's when you get out the sand paper, 220 then 400 then 1000, dry sanding the area.

After it's smooth, use the ValuGard ETR kit and the part is new.

Grumpy
 
You must log in or register to reply here.
Back
Top