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Old 08-05-2021, 08:35 PM   #1
ItWillBeSlow
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Unhappy Rust coming through new epoxy - help

A couple months ago I was spot blasting minor rust pits off the exterior cab while getting the cab ready for primer.

I blew a small pinhole in the metal, just behind the door in the B pillar area. This location is where the interior B pillar and exterior cab sheet metal are overlapped, and there is some seamsiller (or something) in the joint.

I had to notch the interior B pillar metal lip, peel it back, and place some copper here to get the exterior hole filled without constantly blowing holes. It was a mediocre repair but seemed to get the job done. I tapped the notched metal back down and left as-is since its an invisible area.

I noticed today I had rust bubbling under my 2 month old epoxy. The cab has never left my garage and Im surprised and concerned this happened, and so quickly. I obviously did not remove all the rust behind this lip since it is borderline impossible based off the way the cab is constructed.

I scraped the rust bubbles with a screw driver, so that's why they look the way they do. I also have a single small bubble just above my cab corner seam.

This is epoxy over metal, no bodywork or filler hence the ugly seams.

How do I fix this?
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Old 08-07-2021, 12:54 AM   #2
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Re: Rust coming through new epoxy - help

I am ridiculously far away from being considered an expert, but I'm pretty sure the only true way to eliminate rust is to cut it out and put in new steel. Then you'll want to paint/coat all bare metal to prevent future rust.
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Old 08-08-2021, 10:23 AM   #3
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Re: Rust coming through new epoxy - help

Any time there's a pinhole in the body and you paint over it you will shortly see a bubble. I had a panel once it drove me nuts like that. When I ripped the upholstery out behind it there was a rust spot the size of a silver dollar where the bubble was. Did you metal prep the metal ? Metal prep with zinc is great for treating welded seams. I did a video in 2019 , definitely not an Academy Award winner. I took a old fender that was pinholed out and loaded with pits when I was done I threw it behind the shop ,last winter it was buried under two feet of snow. It looks like it did the day painted it and I will post a picture of it. Nothing is better than new metal but sometimes it's not feasible. Heres the video and later on I'll take a picture of the fender
https://www.youtube.com/watch?v=Y-cNT6gjO78&t=207s
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Old 08-08-2021, 12:51 PM   #4
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Re: Rust coming through new epoxy - help

https://mail.google.com/mail/u/0/?ta...cLcDbMDzLWSXfm
And outside in the elements for 2 years. Pay particular attention to the edges you notice the rust has not crept beyond that edge and there's no rust bleeding through primer anywhere In an ideal application you would apply two coats of this primer and then an epoxy surfacer over it and then your top coats. In the Industrial Coatings industry this type of system is used for maximum corrosion resistance in saltwater exposure applications.

Last edited by lupo; 08-08-2021 at 12:58 PM.
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Old 08-08-2021, 06:10 PM   #5
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Re: Rust coming through new epoxy - help

It LOOKS like that rusted thru from the back...
Was the other side of the metal repaired/treated/cleaned/painted?
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Old 08-09-2021, 10:15 AM   #6
ItWillBeSlow
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Re: Rust coming through new epoxy - help

Quote:
Originally Posted by Flying Hamster View Post
It LOOKS like that rusted thru from the back...
Was the other side of the metal repaired/treated/cleaned/painted?
No, I did not clean up the back side as stated in the original post.

Getting behind this “lip” is a bit of a challenge, that’s why the repair you can see in the interior photos is so ugly. I don’t know how to cut this 3/4” lip without cutting all the panels around it. It is almost impossible to get a cutoff wheel or Dremel back here.

I am going to try to cut on an angle and bend the lip back, sandblast and prime behind it, and seal it. Open to recommendations for the best way to work in the corner.
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Old 08-14-2021, 09:41 PM   #7
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Smile Re: Rust coming through new epoxy - help

Bump- I know a few others have repaired something in this area before? Robert? Lorne? SOS
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Old 08-15-2021, 10:55 PM   #8
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Re: Rust coming through new epoxy - help

The deep pits on the vertical surface here are concerning.. Red flag Number one. You don't normally see such pits on vertical surface. This is where I would have broken out the ice pick and find out exactly how solid things are.


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Red flag number two is holes appearing when media blasting, especially that far up on a panel. Again, this is a case where I break out the ice pick and see how solid things are.. Your post is a good case in point that seldom are pits an isolated occurrence.. This also suggests you need to check out everything inside the cab for other rust areas.. It came from somewhere.. The rust inside on the lapped panels is likely from condensation drainage. The seam sealer you saw is likely similar to that I have seen, installed hap hazardly where water intrusion or entrapment is entirely possible. But it doesn't explain the pits on the outside surface of the door jamb.

Red flag number 2A... If you weld up a pit there are likely others in the general vicinity. The electrical current that the panel sees from welding will activate those hidden pits where they will come through more quickly than had they not been exposed to the current. The ones you didn't find will come through your fresh paint job within about two years.. Not that it shouldn't be repaired, but it may need more extensive work than you had planned. In my shop that lapped area would be opened up to see exactly what is there..

Metal repairs are cheaper before your final paint finish goes on. Find out how extensive the damage is now..
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Old 08-16-2021, 06:52 AM   #9
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Re: Rust coming through new epoxy - help

Thanks Robert. I am planning to peel back that inner lip to see what’s behind it as soon as I finish working my my doors. I’m not sure how I am going to cut it due to the angle and location, if you have a recommendation please let me know.

Rhetorical question here: I guess I understand the need to open up areas where you remove rust to make sure it’s all out, or properly clean and seal the backside of the welds. I’ve been able to to this on about 90% of my repairs and I usually repair more than needed if I can. What about areas where this is impossible? For example, I have had to patch some small areas in my a pillar, the bottom ridge of the back glass in the cab, a small piece up above the door opening. These are inaccessible in all cases and that would apply for about any restoration out there right? . Are you saying these repairs will show up? Or is that realistically only if there was a reasonable amount of rust remaining and the weld wasn’t very clean?
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Old 08-17-2021, 11:55 AM   #10
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Re: Rust coming through new epoxy - help

Pin holes are just the tip of the iceberg. The real damage and pitting is on the back side that you can't see. All around the pinholes, the metal will be too thin to either grind or weld to. Any other repair method other than cutting out the rusty metal and welding in a patch panel will only be a temporary band aid, and the rust will come back.

You can try a rust conversion product that converts the properly prepared rust to hard surface but that is not a fix for the pinhole. It looks like salt road spray was getting forced back there. That area behind the panel should be sprayed out to remove the salt coating, then loose rust brushed away, cleaned again, then treated with a rust conversion product to protect the existing areas from further rust out.

The pinholes repair is the tough part. You will find you need to remove at least 2" from all around the pinholes to get to existing metal strong enough to weld in the repair panel. Once that rust area is cut out, then you have access to the rest of that area behind the panel, to clean, prep, and apply rust converter.

I would consider apply a undercoating material over the back of the panel once the metal repair work is done and all the rust converter on the rest of the panel is cured. This will help future damage from salt and road wash.
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Old 08-29-2021, 09:27 AM   #11
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Re: Rust coming through new epoxy - help

Good rust work starts from the inside out. This area is going to have to be opened up, cutout, and patch installed. Open It up the you can clean it up with a phosphoric acid solution and follow it with good anti-corrosive sealer. On your next trip to Harbor Freight pick up a couple of engine cleaning guns in the air tool section. Have used these things for years to spray rust remover / and sealers in hard-to-reach areas. U punch a hole ,put the nozzle against the hole and give it a quick blast. This engine cleaning gun will blow paint and rust remover about 3 ft and it's great for rockers and windshield posts. Good luck with your project.
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Old 09-06-2021, 10:38 PM   #12
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Re: Rust coming through new epoxy - help

Ive been working on this repair and thought I would post an update.

I cut out the interior B-pillar lip to see what caused this. I had a ~1" and ~.5" patch of rust between the panels where the rust came through the exterior and where I blew a pinhole. Other than this, the metal above and below this area was clean. There is some sort of factory sealer/adhesive here, which you can see in the photos. It looks like a ribbon on the interior of the panel, on the cab metal. I'm not sure if water somehow got behind this material over the years and caused this issue, or what. I cut out these areas and decided not to dig any further since it looked clean and I did not modify or patch any other metal in this area.

Some pictures of interior and exterior where I cut out - 1st pic shows the rust from the inside' 3rd and 4th pic are patched areas. Luckily I had this metal leftover from the cab corner.
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Old 09-06-2021, 10:42 PM   #13
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Re: Rust coming through new epoxy - help

Primed the inside of the repaired cab metal and put part of the removed B-pillar lip back in. I put more in than I show in the photo, but it is not exactly as removed.

I welded it back up from the outside as well. This is another area unfortunately where you will not be able to prep or paint your welds from the inside. I sprayed some eastwood sealer in the crevice from the backside, and will also probably fill this area with seam sealer when I am closer to paint.
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Old 09-06-2021, 10:48 PM   #14
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Re: Rust coming through new epoxy - help

Good job
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Old 09-16-2021, 10:20 AM   #15
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Re: Rust coming through new epoxy - help

nice work, now you never have to worry about it again..... at least not in our life time
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