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Rust near roof rack mounting points

1001 Views 28 Replies 11 Participants Last post by  diytech
Hey ya’ll! I’m putting roof rack adapters on and decided to touch up some areas where the paint had chipped away. I was fiddling with this tiny spot and ended up finding what looks like a good amount of rust underneath and was shocked at how it easily it all flaked off. I had been using clean metal primer on certain spots, there’s no way this could have anything to do with it right? Any suggestions on what to do, or can I just spray some paint on there and call it a day? Thanks!
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Normally the galvanized surface on the PM's sheet metal would prevent that kind of thing. But it sure looks like a metal roof stud mount had been on there at one time, and gradually rubbed through the paint, some body putty, and the galvanizing layer. That's one reason I chose a roof stud mount made from plastic and with a large surface area on the bottom.

I'd say remove all the loose rust, and just follow up with a rust converting product like POR15 to stop the rust creep. Then just top coat with Mopar spray laquer to match the color (the POR15 should not be exposed to sunlight).
 

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Discussion Starter · #4 ·
Normally the galvanized surface on the PM's sheet metal would prevent that kind of thing. But it sure looks like a metal roof stud mount had been on there at one time, and gradually rubbed through the paint, some body putty, and the galvanizing layer. That's one reason I chose a roof stud mount made from plastic and with a large surface area on the bottom.

I'd say remove all the loose rust, and just follow up with a rust converting product like POR15 to stop the rust creep. Then just top coat with Mopar spray laquer to match the color (the POR15 should not be exposed to sunlight).
Doesn’t seem to end. Could water have pooled around the cracks and done this? So best method would be to remove until I find the edges and then treat with rust reformer? Thanks again!
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That's very unusual for the PM. Do you know if the van was wrecked and repaired in that area? Do you by chance carry kayaks on the roof or park by the ocean? Or carry another item that might be allow salt or other contaminants to pool on the roof and into the cracks in the sealant?

I would scrape away as much of the loose stuff as possible until you get to clean metal around the edges. The problem is rust will likely extend under that mounting tab which will be inaccessible. Not ideal, but IMO not worth removing it to fix. Just hit the rust with a wire wheel or even better a spot sandblaster if you have access to one. Flush it all out with denatured alcohol and follow it up with POR15 or Chassis Saver (Probably a couple coats) and then scuff and paint to match. Keep an eye on it and touch up as needed an it'll probably last the life of the van.
 

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Is it really rust or metal flakes on the paint from drilling or cutting? It’s hard to tell from the photo. It sorta just looks as if the paint has peeled off.
 

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Discussion Starter · #10 · (Edited)
Update: Seems to exist only around the mounting tab area, but it made its way underneath the channel moulding strip. Also learned that it looks like those long strips are partially made of bondo? News to me.

I’m tempted to make a sliver and check the other mounting points as well. Would pouring some rust reformer or something similar along those creases and hope it leaks underneath be of any benefit?
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My 2¢... Clean up/off any flaky paint. There may be some rust under the layers of sheet metal?? I would probably use some Penetrol oil base paint additive (hardware store). It is a thin penetrating oil that will dry up in a day or two. It will creep into tight places and seal. Makes an excellent base for any top coat. I would probably soak it into all those cracks and wipe it off. Once dried you can top coat with any good paint.

The Por15 noted is good stuff BUT very expensive. (You only need a small amount) Once opened it will quickly start setting up. For anyone using a trick is to not open lid... just punch a small hole to get paint then seal with a screw. I got a few months with this trick.

The Tremclad is interesting and comes in a spray can. Thanks for mentioning. I was not aware of it. ---KenA
 

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The outline of your rust area (where the water probably entered) looks suspiciously like the perimeter of a Vantech mounting base, but who knows?

Good tip on the POR15 storage @Ken Allan. Also, if you have a food vacuum sealer, you can seal up the little cans whole. I got a couple of years out of one that way.

A couple of things I like about the POR15 is that it forms a really tough barrier, and it's also not very viscous right out of the can (flows into crevases nicely).
 

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It does look suspiciously like a roof mount scar. But what looks like Bondo is probably just factory seam sealer. Instead of painting after clean up, I'd just cover the (wide) area with white Eternabond tape. Cut a hole to slip over the mounting tab.
 

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I have the identical thing happening with my 2014. No roof rack scar, just creep from cracked factory sealant around the mount. That panel of the roof must not be galvanized, as I have other areas with paint chipped off down to the metal/primer, and no rust at all. I flaked off everything that would come off, brushed the rust off, and used flex seal only because I didn't have a window of time to use POR15. POR15 in the total solution, so I will eventually strip the flex seal and use the POR15.
I restored an old golf cart a while back, and the battery tray was corroded badly from the battery acid, and all I did was pressure wash off the loose rust, and didn't even remove the surface rust that was left, used POR15 black paint, and that thing held perfectly for YEARS!
 

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Discussion Starter · #15 ·
My 2¢... Clean up/off any flaky paint. There may be some rust under the layers of sheet metal?? I would probably use some Penetrol oil base paint additive (hardware store). It is a thin penetrating oil that will dry up in a day or two. It will creep into tight places and seal. Makes an excellent base for any top coat. I would probably soak it into all those cracks and wipe it off. Once dried you can top coat with any good paint.

The Por15 noted is good stuff BUT very expensive. (You only need a small amount) Once opened it will quickly start setting up. For anyone using a trick is to not open lid... just punch a small hole to get paint then seal with a screw. I got a few months with this trick.

The Tremclad is interesting and comes in a spray can. Thanks for mentioning. I was not aware of it. ---KenA
Thanks so much. Could I theoretically use the Penetrol to flow into the tight spots/crevices and then add the POR15 to the more accessible areas? Or best to do one over the other?
 

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In my opinion Por15 is not the product to use for this application. It's made to be applied to bare or rusty metal (not other paint) and is NOT UV resistant so it needs to be top coated with something else. You could also thin down some good paint and let it soak into cracks then paint over that.

Whatever you do you need to check on it a couple times a year to catch any new developements.
 
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In my opinion Por15 is not the product to use for this application. It's made to be applied to bare or rusty metal (not other paint) and is NOT UV resistant so it needs to be top coated with something else.
It seems like this version of POR15 can be applied to bare metal, doesn’t need a topcoat and is UV resistant. Top Coat
 

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Discussion Starter · #18 · (Edited)
I have the identical thing happening with my 2014. No roof rack scar, just creep from cracked factory sealant around the mount. That panel of the roof must not be galvanized, as I have other areas with paint chipped off down to the metal/primer, and no rust at all. I flaked off everything that would come off, brushed the rust off, and used flex seal only because I didn't have a window of time to use POR15. POR15 in the total solution, so I will eventually strip the flex seal and use the POR15.
I restored an old golf cart a while back, and the battery tray was corroded badly from the battery acid, and all I did was pressure wash off the loose rust, and didn't even remove the surface rust that was left, used POR15 black paint, and that thing held perfectly for YEARS!
Tricky situation since POR15 might not work on painted spots underneath the crevices. I’ll likely give Penetrol a shot to soak in the crevices and then try POR15 for the cleaned bare metal spots that are out in the open.
 

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Tricky situation since POR15 might not work on painted spots underneath the crevices.
Others may disagree (I'm fine with that), but I'll tell you my experience with the stuff.

Basic POR15 product is neither mysterious nor miraculous. It's just tinted, low viscosity cyanoacrylate (i.e. super glue) in a can. It can adhere to many surfaces as long as they are not mirror smooth or flex too much (which would tend to loosen the adhesion). It doesn't convert rust, but rather completely surrounds, encapsulates, and binds the iron oxide (rust) on metal. It's also very strong when cured (on it's own), so that's where it comes in handy in bridging perforations and filling pits from rust. A side benefit in using it on rusty surfaces is that it will absorb water molecules as part of it's curing process (in fact, that's required), and getting rid of water is good where there is a concern about rust.

I don't use it everywhere, but just where it's properties will be most useful. When there is need to fill pits and rebuild holes, there's not a better choice IMO. In situations like yours where it's impossible to get to all the hidden surfaces, it's better to complelely encapsulate the area (where the product excels) rather than try to convert all the rust (i.e. as with phosphoric acid-based rust converter paints and products) because you simply can't get it all. If even the tiniest amount atmosphere can get into the area in any way, the rusting will continue.

The only disadvantages are that you'll need to roughen any smooth top surfaces (i.e. metal, paint, etc.) before applying, and then absolutely paint over it after it's cured (especially if it will be exposed to sunlight). In fact, it can be used right up to the line where the paint remains, and then smooth a little with wet-dry paper before painting over.

I’ll likely give Penetrol a shot to soak in the crevices and then try POR15 for the cleaned bare metal spots that are out in the open.
The POR15 would be the same with clean metal as with paint...just need to roughen it up a little where it would be subjuct to wear. However, use the Penetrol-enhanced oil paint as a top coat for the POR15, not the other way around. One to encapsulate the wound, and the other to protect and seal.
 

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I’ll likely give Penetrol a shot to soak in the crevices and then try POR15 for the cleaned bare metal spots that are out in the open.
This has been outside in the weather for 20 years.

I coated/painted it with Penetrol (after a muriatic acid bath and letting it aquire some surface rust patina) when I installed it and once more about 8 years ago. It's ready for another coat. Penetrol flows into all the cracks/crevices and protects really well.

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