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I am replacing a rear bumper cover on my 2004 Subaru Impreza, and the cheapest deal I can find is a brand new, unpainted unit. My question is whether it is important to paint it, they way it would be important to paint unfinished metal parts. It's plastic, so rust obviously not an issue. Is there something I'm missing?

It will come black, my car is dark green, and the trim is meant to be grey, so I'm not really too concerned about the aesthetics, and would love to save the cash on a professional paint job.

I would be willing to do the paint job myself, but the appropriate paint layers add up to quite a lot, even without professional labor. Is there a cheaper solution to painting this thing? I'm guessing a few cans of grey spray paint won't get the job done, and I'd prefer to leave it black if the alternative is a poor paint job.

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    If you are bent on saving cash, its perfectly reasonable to leave it the way it is, many taxi drivers do this in my country , instead of repainting they just leave it black , unless your car is milky white or silver it will not look that bad. Don't do paint job on your own, unless you are a professional. trust me , i have ruined a fuel tank on a bike. :-) – Shobin P Jul 20 '15 at 14:44
  • You'll be surprised at what can be achieved with spray cans, sandpaper and a steady hand. Just be sure to prep the surface properly before and between coats. – Captain Kenpachi Jul 20 '15 at 14:51
  • Painting with spray can is an option. The preparation really make the difference. See you yourself here youtube.com/watch?v=LHA0jhp3CSM Plus it's also a subaru (I don't have any affiliation with those guys, I simply like their vid) – Rémi Jul 20 '15 at 16:58
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While painting a bumper at home is always possible, you would need to:

  • Prepare the surface correctly: clean off the products used to de-mold the plastic, sand the part if there is a granular relief motive.
  • Apply the appropriate primer. Specific primers may be used for the paint to stick to the plastic correctly, and even better primers that have some flex to them in order to avoid cracks when dry.
  • Apply 2-3 layers of paint. Not too many, or the end result may be too thick and again, cause cracking.
  • Several layers of varnish may also be needed, specifically for metallic paints.

If you do not have access to professional paint -and the installation to apply it correctly (dust-free shop with filtered ventilation) - chances are the end result will stand out as just what it is - a botch job with spray cans.

On the other hand, there are many vehicles around (mostly little city cars, not Imprezas, but still...) with plain, unpainted plastic bumpers. As you note, the plastic material will hold up perfectly without any need to be painted. The only point to note is that, if exposed to strong sunlight, it will end up going a bit whitish as years go by (5-6 years to be noticeable). There is no legal requirement to paint the bumper, and small scratches and dents will stand out much less than painted.

If the black rear bumper contrasts a bit with the front (painted), you can always also change the front bumper for a second-hand unpainted one, perhaps later on, and the optical impression of the car will be more unified once more.

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    I believe rubber/plastic parts also need a flexible paint additive so as it can flex with the part, or it will get the spiderweb cracks in it. – Pᴀᴜʟsᴛᴇʀ2 Jul 20 '15 at 15:43
  • @Paulster2 Not sure if it's needed if the paint layers are not too thick, I think new automotive paint usually has some additive in it. Not so for spray cans, of course, but layers will (should) also be thinner. Personally, I just do not like painting parts that need to flex, bumpers or sidewall protections, etc. – ALAN WARD Jul 20 '15 at 15:54
  • U-POL plastic primer (or similar) adheres to plastic surfaces better and won't loose it's "grip" on the surface as the bumper naturally flexes. I would always recommend a plastic (or "high build") primer when painting a plastic bumper. – Steve Matthews Jul 20 '15 at 15:56
  • @SteveMatthews Yes indeed, a good paint is no use if the primer is cracking or peeling. Also clean well the surface (de-grease) if it is a new part. But we are starting to talk about professional materials here, not sure this is something I would apply with the vehicle parked at the street corner or in the family garage. – ALAN WARD Jul 20 '15 at 16:01
  • Paulster2 and SteveMatthews: have edited your comments into the answer. – ALAN WARD Jul 20 '15 at 16:18

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