7

After driving around with a huge hole in my front bumper cover for two years, I finally decided to replace it myself. I bought a new bumper cover through my local friendly auto body supply store, along with a gray primer and a custom-made single stage paint that they loaded into a spray can for me.

I took it home, sanded it with the gray scotch brite pad, wiped it down, and applied two layers of primer, waiting a full day and sanding between each coat. I then applied two layers of my custom single-stage paint, again waiting a full day between each coat.

After installing the painted bumper and waiting a few more days, I scrubbed at it by hand with an old sock and some Turtle Wax Premium Polishing Compound. It now looks like this:

Painted new bumper cover on Mazda 3

As you can see, it looks good, but nowhere near the glossiness of the rest of my car (even 7 years after it came off the factory line). The one run you see below the left headlamp was my ill-advised attempt to increase the sheen by applying more paint.

Here is a closeup of the difference between my paint job, and the factory paint:

Closeup of DIY paint job

As you can see, I can see my reflection in the factory paint.

What critical step am I missing?

I see a lot of auto forums that casually mention "cutting" the paint, as in the phrase "cut, buff, and polish". What is "cutting" a new paint job, and is this the step I'm missing?

I also see references to "rubbing compound", which is supposed to be a coarser grit compared to the polishing compound. Could this be what I'm missing?

  • I'm not a paint & body guy, but every one I have talked to suggested to me you put down one layer, then let it dry until it gets tacky (about 10 minutes or so), then lay down your next layer. I guess since you sanded between layers you should have good adhesion, but ... Anyway, I hope you can get a real body guy on here to explain what to do next, but I would suggest that cutting then buffing are in your future. Right now I'm guessing you are at an "orange peal" state. – Pᴀᴜʟsᴛᴇʀ2 Jul 30 '15 at 22:35
  • So, what does "cutting" mean? I see the term used everywhere, without any definition. Do I get a katana and start slicing away at my bumper? Do I start up FruityLoops and lay down a drum roll? – alexw Jul 30 '15 at 22:52
  • 1
    Think of "cutting" or "cutting in" as a liquid sand paper. I found this video on YouTube which shows how Meguiar's Ultra-Cut 105 should be used. Cutting compound is used to clean up scratches left behind by 1500+ grit sand paper, which is a step before cutting. Polishing cleans up any leftovers from the cutting. Then you put a good wax on after that. – Pᴀᴜʟsᴛᴇʀ2 Jul 30 '15 at 23:58
  • If you are wondering, I know the basic process, but have never done it before, so I could just as easily be talking out my backside. I don't want to give you bad information about the "how to" because I don't want to be the cause of you messing up the finish. – Pᴀᴜʟsᴛᴇʀ2 Jul 31 '15 at 0:05
  • This is also another good video by Meguiar's which shows the entire process from sanding through wax. – Pᴀᴜʟsᴛᴇʀ2 Jul 31 '15 at 0:15
4

The paintwork looks like it's suffering from orange peel. It may be that you need more or thicker coats on it.

To get a nice shiny finish from what you have you effectively need to flatten out the outer surface of the paint finish. There are a few ways to do this. As stated previously, cutting paste can be quite effective but may take quite a long time. I'd personally get some very high grade sand paper. I'd get something like 1500 or 2000 grade wet and dry. Consider 1200 grade if that's all that's available but go easy with it. Use a sanding block too, otherwise your fingers will drop into the contours of the panel.

Get a bucket of luke warm water and put a TINY (like a drop or two) amount of washing up liquid in it. Keep the sand paper very wet and keep wetting it. If you go too hard on this you may go through the paint and back to the primer.

After this you can start using cutting compound (cutting paste) before finishing with a good wash, polish and wax.

In future, if you paint a "wet line" into the panel you can effectively paint shine in but if you put too much on you get runs which you also have to buff out so it's a case of practice, practice, practice. I have to say it does look good for a first attempt though :-)

  • Thanks, yes I am starting to think that I might need another coat. I noticed that some of the primer has started to show through after a light sanding with the scotchbrite. After that, I will try ordering some 1500 and 2000 grit sandpaper. This will all have to wait until I'm back from vacation, unfortunately :( – alexw Jul 31 '15 at 16:29
  • Just as an update: the 1500/2000/2500 grit sandpaper indeed seems to have been the missing step. Also, I probably should have smoothed the raw plastic out better before painting - otherwise, those small bumps end up showing through when you try to sand to a perfectly flat, high gloss finish. – alexw Jul 26 '16 at 0:30
3

I'm not a paint & body guy, but every one I have talked to suggested to me you put down one layer, then let it dry until it gets tacky (about 10 minutes or so), then lay down your next layer. I guess since you sanded between layers you should have good adhesion, but ... I would suggest that cutting then buffing are in your future. Right now I'm guessing you are at an "orange peal" state.

So, what does "cutting" mean? I see the term used everywhere, without any definition. Do I get a katana and start slicing away at my bumper? Do I start up FruityLoops and lay down a drum roll?

Think of "cutting" or "cutting in" as a liquid sand paper. I found this video on YouTube which shows how Meguiar's Ultra-Cut 105 should be used. Cutting compound is used to clean up scratches left behind by 1500+ grit sand paper, which is a step before cutting. Polishing cleans up any leftovers from the cutting. Then you put a good wax on after that.

This is also another good video by Meguiar's which shows the entire process from sanding through wax.

0

Did you not spray a clear coat as the last coat? The glossyness comes from that layer.

  • This is supposed to be a single stage paint, so only one layer. I agree he could get more gloss with a multi-stage, though. – Pᴀᴜʟsᴛᴇʀ2 Jul 31 '15 at 11:44

protected by Community Aug 20 at 13:52

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