Where did I go wrong painting bumpers?

AndyA

AndyA

2006 TJ X
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Tucson, AZ
Steps I took:

1. Machine sanded dry at 320 grit
2. Cleaned with Dawn Powerwash
3. Cleaned with neat Simple Green.
4. Dried with paper towels

At this point the metal was squeaky clean and the paper towels were clean looking.

5. Sprayed with Rustoleum Self-etching Primer, several coats. Air temp was around 72F
6. Waited 24 hours

I could still scratch the primer with a fingernail but decided to try wet hand sanding 320 grit anyway. And... it's just coming off.

So where is my mistake? I know I now have to sand all of this off but what should I do differently the second time around? Next time I will just do a test area first.

First pic below is before priming.

Thanks, Andy

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I'm wondering if the Dawn and/or Simple Green left something on the metal surface to affect adhesion of the primer. Never used either of those myself. I'm in the rust belt and constantly doing touch ups. Usual process is to grind off surface rust, sand to bare metal, blow it off with compressed air, rub the area down with alcohol or sometimes spray with brake cleaner, then prime and paint.
 
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AndyA said:
Steps I took:

1. Machine sanded dry at 320 grit
2. Cleaned with Dawn Powerwash
3. Cleaned with neat Simple Green.
4. Dried with paper towels

At this point the metal was squeaky clean and the paper towels were clean looking.

5. Sprayed with Rustoleum Self-etching Primer, several coats. Air temp was around 72F
6. Waited 24 hours

I could still scratch the primer with a fingernail but decided to try wet hand sanding 320 grit anyway. And... it's just coming off.

So where is my mistake? I know I now have to sand all of this off but what should I do differently the second time around? Next time I will just do a test area first.

First pic below is before priming.

Thanks, Andy

View attachment 508699

View attachment 508700

View attachment 508701
Click to expand...

I ran into this when I was painting my front bumper on the old Jeep… wipe everything down with alcohol or acetone before priming… Etching primer is not a sanding primer It’s just an adhesion primer and you still need to put regular primer over the top of it in layers and that’s the one you sand before painting… and also you don’t need multiple coats of etching primer…
 
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AndyA said:
Steps I took:

1. Machine sanded dry at 320 grit
2. Cleaned with Dawn Powerwash
3. Cleaned with neat Simple Green.
4. Dried with paper towels

At this point the metal was squeaky clean and the paper towels were clean looking.

5. Sprayed with Rustoleum Self-etching Primer, several coats. Air temp was around 72F
6. Waited 24 hours

I could still scratch the primer with a fingernail but decided to try wet hand sanding 320 grit anyway. And... it's just coming off.

So where is my mistake? I know I now have to sand all of this off but what should I do differently the second time around? Next time I will just do a test area first.

First pic below is before priming.

Thanks, Andy

View attachment 508699

View attachment 508700

View attachment 508701
Click to expand...

1. Clean with Alcohol
2. Sand smooth. 320 is good, but you can start at 120, 220, then 320 if you’re anal. Wipe down with alcohol between each sanding
3. Self etch prime. Follow directions on can. Usually 3-5 minutes between coats. 2-3 coats is fine. This is just to give the top coat something to bite on.
4. Usually it’s 30 minutes after your last self etch coat that you start your top coats, but follow the can. If you wait 24 hours you have to lightly sand. Why bother. Just start 30 min after your last self etch
5. Do your 2-3 top coats and chelax for several hours. Probably won’t totally cure for 24 hours, but you should be good to go.
 
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Thanks - great advice!

I've managed to use my orbital sander to get most of the old primer off but is there an easy way to remove it in the areas I couldn't reach, besides sanding by hand? Some chemical? I tried mineral sprits and brake cleaner - didn't do a thing.

Thanks, Andy
 
Clean with Mineral Spirits until towels show a clean surface. After completely dry, start by spraying a very thin primer skim coat (90% coverage) where you can barely see the base metal. Wait 15min. and apply a full coat of primer. Wait another 15-30min. and spray a very thin paint skim coat (90% coverage) where you can barely see primer underneath paint. Wait a final 15-30min. or so and apply final paint coat. I like the Rust-Oleum Professional line of spray paints.
Don't wait longer than 1hr to recoat or you'll have to wait a day or two and then have to sand surface for paint to bite.
 
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AndyA said:
Thanks - great advice!

I've managed to use my orbital sander to get most of the old primer off but is there an easy way to remove it in the areas I couldn't reach, besides sanding by hand? Some chemical? I tried mineral sprits and brake cleaner - didn't do a thing.

Thanks, Andy
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Lacquer Thinner. Citristrip is some amazing stuff for paint removal but it will probably come right off with the Lacquer Thinner.

https://www.amazon.com/Citristrip-QCSG801-Paint-Varnish-Stripping/dp/B07LF8T6PM/?tag=wranglerorg-20
 
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On a test area I did the following:

1. Cleaned with brake cleaner
2. wiped dry
3. dry sanded 150 grit with an orbital sander
4. Wiped with paper towel
5. Sprayed light coat of Rustoleum self-etching primer
6. Waited two minutes
7. Sprayed another coat

Four hours later it is acting like the previous attempt. The primer can be scratched off with a fingernail. It feels a bit clay-like.

:confused:

Andy
 
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AndyA said:
On a test area I did the following:

1. Cleaned with brake cleaner
2. wiped dry
3. dry sanded 150 grit with an orbital sander
4. Wiped with paper towel
5. Sprayed light coat of Rustoleum self-etching primer
6. Waited two minutes
7. Sprayed another coat

Four hours later it is acting like the previous attempt. The primer can be scratched off with a fingernail. It feels a bit clay-like.

:confused:

Andy
Click to expand...

Use a proper wax and grease remover before paint.

Dish soap, simple green and brake clean are not proper paint prep cleaners, they are leaving residue behind, more than likely why you are not getting proper adhesion.

Use something like this.

385E0562-F11C-40F9-BA48-F3C1B0B85AB8.png
 
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AndyA said:
Thanks - great advice!

I've managed to use my orbital sander to get most of the old primer off but is there an easy way to remove it in the areas I couldn't reach, besides sanding by hand? Some chemical? I tried mineral sprits and brake cleaner - didn't do a thing.

Thanks, Andy
Click to expand...

There’s no reason to remove what won’t come off. It has good adhesion. Leave it!
 
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I use acetone a lot when painting. Makes a good surface prep wipe, its GREAT at removing previously applied spray paint, and its a pretty good degreaser as well.

My typical process on new steel is to clean it and get all the mfg garbage off. Then, if its necessary, sand it (for a bumper, I wouldn't take the time). If sanding, you clean it again. On bare steel, I don't like to use water...because of the flash rust you need to deal with. If you didn't sand, once the steel is clean, hit it with primer (self etch is fine). I don't typically do another layer of primer over the self etch, and I definitely don't sand it. Color coat and go.
 
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Mike_H said:
I use acetone a lot when painting. Makes a good surface prep wipe, its GREAT at removing previously applied spray paint, and its a pretty good degreaser as well.

My typical process on new steel is to clean it and get all the mfg garbage off. Then, if its necessary, sand it (for a bumper, I wouldn't take the time). If sanding, you clean it again. On bare steel, I don't like to use water...because of the flash rust you need to deal with. If you didn't sand, once the steel is clean, hit it with primer (self etch is fine). I don't typically do another layer of primer over the self etch, and I definitely don't sand it. Color coat and go.
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This here,I think he is overthinking this.
 
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On my fenders I did Acetone to clean, sanded with scotch brite red pad, acetone again, dry. During the sanding, I probably spend an hour per each fender. Then I did 2 coats primer, wet sand after 15 min with higher grit scotch brite, dry sand after 4 hours with same level pad, and then applied the color (3 coats I think?). Clear coated 30 min after.

I had these fenders on for 4 years and it was a daily driver then too. They looked pretty good when I finally took them off to sell. The rock rash obviously strips the paint away, but the primer underneath stayed put.

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After applying Krylon Fusion I have to wait seven days for it to fully cure before I can start installing the lights, winch, etc. on it?

Thanks, Andy
 
Moglocker said:
This here,I think he is overthinking this.
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When I painted the factory JK Rubicon bumper for my JT, I cleaned with Rustoleum paint prep spray, scuffed with scotch brite, cleaned again with the prep, and used Rustoleum texture black…. It’s been 2 1/2 years now with no issues.
 
AndyA said:
After applying Krylon Fusion I have to wait seven days for it to fully cure before I can start installing the lights, winch, etc. on it?

Thanks, Andy
Click to expand...

I got my Under cover fabworks bumper in yesterday afternoon, wiped it down with acetone, put 2 coats of gray rustoleum primer on it and 3 coats of satin black rustoleum paint on it… I mounted it this morning … I figure it can cure on the Jeep… that’s the way I’ve always done it and I’ve never had a problem. YMMV…

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