Bumper Pitting and Polishing

[kevinr1247]

So, severe pitting on the front bumper of my '82. I don't want to spend a fortune restoring. Is there a method from bringing back a little shine and removing the pitting? I've read wet sanding and then finer and finer sandpaper. Any recommendations? The previous owner just covered it all with spray paint, so that was fun to remove. I expected that something was being covered. Here's a pic...

IMG_2201.jpg

[osburn383]

Yeah that's some pretty heavy oxidation.
You will most likely have to end up removing the anodizing and refinish the metal.

They sell so called oxidation removal kits but i have yet to find many positive reviews on them.
It does make the oxidation slightly less noticeably but not like new.

You can use oven cleaner as a easy sourced chemical to remove the anodizing.
You could pick up some sodium hydroxide (lye) as well to remove it.

Then you would need to take some sand paper to sand past any pitting.
If no pitting you could go over it with a red scotch bright pad and give a uniform grain and wax, metal sealant, or clear coat.
OR
Polish it with a buffer for a mirror shine and wax, metal sealant, or clear coat.

[kevinr1247]

Thanks for the process. So, oxidation is the issue and it's cutting through the anodizing....or the anodizing was penetrated thus causing the bare aluminum to oxidize? Is that correct? So then removing the anodize would be the next logical step it seems. And there may be pitting as well. I expect that the bumper saw some road deicing chemical at some point which may be the cause.

[Thecatmilton]

You may want to find a place that polishes aluminum rims and have them do it for you. It will be a lot easier and it will get done faster.

[SoCalE21]

It's actually pretty easy.
You have it right, you need to remove the anodizing and then sand/polish it up.
The hardest part is getting a "bin" large enough to hold the bumper and the water/lye solution.
A kiddie swimming pool works.
Fill it with water high enough to cover the bumper, mix in the lye (can get it on Amazon), and wait until the anodize is removed.
Don't let it sit too long, or you can cause "waves" in the bumper (the lye can get pretty aggressive on the aluminum if you let it sit for hours and hours after the anodize is gone).
30 minutes to an hour is a rough estimate.
You know when it's done when you can easily polish the bumper to a high shine.
If there is pitting, you may need to sand the bumper before polishing, to get rid of the pits. Start with a heavy grit, move to finer, then polish.
I've done it, it's not too bad. You could take it to a polish shop, they'd do the same thing.

[kevinr1247]

It's actually pretty easy.
You have it right, you need to remove the anodizing and then sand/polish it up.
The hardest part is getting a "bin" large enough to hold the bumper and the water/lye solution.
A kiddie swimming pool works.
Fill it with water high enough to cover the bumper, mix in the lye (can get it on Amazon), and wait until the anodize is removed.
Don't let it sit too long, or you can cause "waves" in the bumper (the lye can get pretty aggressive on the aluminum if you let it sit for hours and hours after the anodize is gone).
30 minutes to an hour is a rough estimate.
You know when it's done when you can easily polish the bumper to a high shine.
If there is pitting, you may need to sand the bumper before polishing, to get rid of the pits. Start with a heavy grit, move to finer, then polish.
I've done it, it's not too bad. You could take it to a polish shop, they'd do the same thing.

Couldn't I just sand off the anodizing?

[pommeree]

You may want to find a place that polishes aluminum rims and have them do it for you. It will be a lot easier and it will get done faster.

A wheel place. Genius!
I vote for that over the kiddie pool full of lye.

[kevinr1247]

You may want to find a place that polishes aluminum rims and have them do it for you. It will be a lot easier and it will get done faster.

Yes, only where I am, there's not a big market for wheel polishing unfortunately. This'll be another DIY gig.

I'm debating whether to just sand or chemically remove the anodize. I'm leaning towards chemistry myself. Does it make a difference or is it just a matter of time?

[kevinr1247]

And so it begins....I'm going to test a bit of oven cleaner and then start with 240, then move to 400. I think the 400 is too fine to start based on the test. I think the 240 will be fine.

IMG_2202.jpg

[osburn383]

And so it begins....I'm going to test a bit of oven cleaner and then start with 240, then move to 400. I think the 400 is too fine to start based on the test. I think the 240 will be fine.

Yeah the chemical strip will just keep you from sanding so much as the anodizing is harder to sand through.
You could always be the greased lighting and soak it on some rags then shrink wrap it to the bumper to keep it from drying out.

[SoCalE21]

No way you're gonna sand the anodizing off.

Not sure how the oven cleaner is going to work. Seems like you'd need quite a bit of it, and it would be a lot more work and less consistent coverage than simply letting the bumper soak 45 minutes in water and $5 work of lye.

Always worth a shot experimenting, though, if you have the time and patience. I think you'll quickly see how futile sanding anodizing is! You're also going to have to do a lot of finer and finer sanding to get the rough sanding scratches out. 240 is going to put some very deep scratches in the bumpers.

[SoCalE21]

My bumpers looked as bad as yours. With my method and very little time and effort, this is how they came out

Attachment 607990

[SoCalE21]

Will it open if you click on it?

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https://www.bimmerforums.com/forum/a...hmentid=607990

[Thecatmilton]

Will it open if you click on it?

- - - Updated - - -

https://www.bimmerforums.com/forum/a...hmentid=607990

Links are dead.

[SoCalE21]

trying againDSC_1376.jpg

- - - Updated - - -

DSC_1378 (2).jpg

[kevinr1247]

So the oven cleaner worked very well, I think. A couple of applications and the anodizing pretty much melted away. The pitting is pretty deep. Something really corroded the aluminum. I'm guessing deicer, so I really had to dig into it to level the surface out, hence the 240.

SoCalE21, once you had the polish, what did you use to seal it all up?

Here's some pics of the progress.

Before sanding and after the oven cleaner...

IMG_2203.jpg

240 then 400...

IMG_2204.jpg

I'm probably screwing it up, but already it's million times better.

[osburn383]

So the oven cleaner worked very well, I think. A couple of applications and the anodizing pretty much melted away. The pitting is pretty deep. Something really corroded the aluminum. I'm guessing deicer, so I really had to dig into it to level the surface out, hence the 240.

SoCalE21, once you had the polish, what did you use to seal it all up?

Here's some pics of the progress.

Before sanding and after the oven cleaner...
240 then 400...
I'm probably screwing it up, but already it's million times better.

That's looking much better already.

[okieflats]

Looks really good. You could just leave the scratches in it, especially since you did all the sanding in a straight line, and it looks like brushed stainless steel. And seal it up with something.

[SoCalE21]

Looks good! Glad the oven cleaner worked to get the anodize off.
I didn't seal mine with anything. I used Meguire's wheel polish on them. They'd stay pretty shiny, I'd just hit them with the polish every 4-5 months.

[Thecatmilton]

You could wax the bumpers. I wax the lips on my wheels to keep them shiny longer.