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iBang

Rust proofing the inside of body welds

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Among the many things I'm going to have to do to my Z, I will need to weld up some patches in a couple areas including the rockers and other places without access to the rear side.

 

In my experience, nothing rusts quite like a fresh weld, so how does everyone go about keeping fresh patches from turning into starting points for rust on our corrosion prone old cars? I've seen a product from eastwood that you drill a hole, spray some rust killer/preventer paint crap in blind every couple feet and then use a rubber or plastic plug over the hole. Seems like a good idea, but does anyone have some firsthand experience?

 

I'm putting a lot of work into my Z and I want to build it to last decades without repair, not years.

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Lots of old guys use motor oil (or other oil mixes) and from the cars I have cut apart, it works very well too and is probably better for metal that already has a little bit of surface rust since it will penetrate much deeper than the waxes or rust converters. Whatever you can do to keep oxygen off the metal and not create voids will work.

Edited by Snailed

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I should have been more specific. I'm worried about the back side of the weld where you aren't going to be painting. For instance a rocker panel - you weld on a patch for some rust repair, but you now have a bare fresh weld on the back side that you can't get at.

Edited by iBang

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I had my car dipped (stripcleaninc.com) so the car was down to bare metal inside and out. I'm planning to apply POR-15 (reduced) using the gun and wand listed here. I'm still welding so I wont be doing it for a couple weeks but the wand is flexible and long enough to get into every enclosed area of my chassis. Until then I'm coating all welds and grinding areas with a zinc phosphate solution Strip Clean uses as part of their dipping process.

 

Applicator Gun:

http://www.amazon.com/gp/product/B000PESJ5E

 

Application Wand (Sprays 180 or 360 degrees)

http://www.amazon.com/gp/product/B0038D7GB2

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I spray the back side of panels I'm welding with 3M High Zinc Weld Thru Primer and also spray Wurth Body Cavity Spray into body cavities through small holes I drill. Be sure to drill those holes on the bottom of the cavity so any water that might get in has a chance to drain.

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It just so happens that while I was at SEMA in Vegas this past week there was a new product out that does exactly what you are looking for, it adapts to the end of the red spray tube that you stick into the nozzle of your normal spray paint can.

 

You can feed it into the body cavity that you need to seal and it sprays 360 degree's of whatever you want to spray it with. The rep suggested their weld through primer with zinc similar to what 240zip said as it allows you to weld and not have to be sprayed with a sealer as it doesn't burn.

 

It's basically an extension that slips over the red spray tube that is flexible with a special spray tip on it that spray's in a circle form to coat the surrounding area as you slowly pull the tube back out of the cavity.

 

 

Unfortunately I have stacks of information I brought back with me that I need to search through to find the company's name but some google searching should turn something up about it. I'll try to go through the pile of stuff tonight and edit this post with the name of the company and the tool.

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In my part of the world there are several speciality liquids used to spray inside (car!) body cavities such as fish oil. Hell of a messy job though if done properly, stuff runs out everywhere. Use a spray gun with a flexible wand tipped with a 360 degree spray nipple

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You may find this article interesting as it is applicable in todays new autos and has relevance to replacement of welded panels in general.

 

 

Advantage Online: 2011 Archives

advantage_online_banner.gif

 

 

 

 

fig_01.jpg

 

Figure 1 - Anti-corrosion compound is applied to enclosed interior surfaces with a wand using access holes.

 

CORROSION PROTECTION TO STRUCTURAL PART INTERIORS

 

There has been a longstanding recommendation to apply epoxy primer, as well as anti-corrosion compound, on the inside of rails and pillars and rocker panels as a last step for structural repairs. Going back as far as the July/August 1988 I-CAR Advantage, in the article “Restoring Corrosion Protection,†is the following step for providing corrosion protection to enclosed interior surfaces: “Apply primer. Two-part epoxy recommended. Then apply anti-corrosion compound.†The reason given, is that on areas where the coatings have been entirely removed, this is a two-step process that is replacing the two original coatings, zinc and E-coat.

 

During research for the recently updated I-CAR course, Corrosion Protection (CPS01), I-CAR asked several product and vehicle makers if this is still the most frequent recommendation. I-CAR was told it is not, due to several reasons. These include possible primer adhesion problems on these surfaces, the lower prevalence of epoxy primer at repair facilities, the increased popularity of self-etching primer, changing primer chemistries, and an increase in the effectiveness of anti-corrosion compound. E-coat is the best corrosion protection material that will ever be applied to a vehicle surface, and aside of the weld backside, the enclosed interior areas have E-coat.

 

Still, there is a concern among repair facilities for longevity of repairs, retaining corrosion warranties, and assurance that there is one more layer of protection, especially in the rust-belt areas. For these reasons, and more, several facilities will continue to apply epoxy primer in addition to anti-corrosion compound to enclosed surfaces as a standard operating procedure.

 

Primer Requires a Cleaned Surface

 

Product makers have a concern with adhesion if these backside areas are not cleaned properly. Any surface to be primed must be cleaned, both mechanically and chemically. If applying epoxy primer inside rails and other structural parts, the surfaces must be cleaned before the part is assembled. This requires sanding followed by a thorough chemical cleaning, especially the joint area backside to remove coatings. There might be access to a rail joint, if the joint is near the very tip of the rail and the rail is open-ended up through the joint location. Other than a situation like that, there isn’t enough access for proper cleaning after welding, so it must be cleaned before assembly.

 

Anti-Corrosion Compound Alone

 

The recommendation from the product makers and vehicle makers that I-CAR communicated with during research for updating the I-CAR course, Corrosion Protection (CPS01), is to apply anti-corrosion compound alone. Anti-corrosion compound, applied as a mist coat using a wand inserted through access holes or from the end of a rail, is designed to protect enclosed areas from corrosion (see Figure 1). The proper application technique should treat the backsides of the welds. Excess material should creep into the flange areas, sealing off those areas from moisture. At least one vehicle maker, Chrysler LLC, recommends a double application of anti-corrosion compound (see Video).

 

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Video: Chrysler Collision Repair Manager Doug Craig explains that Chrysler recommends applying two coats of anti-corrosion compound.

Do Not Use Self-Etching Primer

 

It is still recommended to not use self-etching primer inside enclosed areas, because it doesn’t form a barrier like epoxy primer and would eventually break down. Self-etching primer must be coated with another product, and it would be difficult to see inside an enclosed area whether or not the primer is completely coated by the anti-corrosion compound.

 

Conclusion

 

The recommendation to apply epoxy primer followed by anti-corrosion compound inside an enclosed area is not included in the updated I-CAR course, Corrosion Protection (CPS01).

 

When using this two-step process, the surfaces must be cleaned for the primer to properly adhere. The more general recommendation is applying anti-corrosion compound alone.

 

The instructor-led (live) I-CAR course, Corrosion Protection (CPS01), has been refreshed. It includes updated manufacturer recommendations, as well as an updated presentation. Watch for this course in your area. For course details and to register, visit the I-CAR website.

 

For comments or suggestions on the Advantage Online, please contact I-CAR at

[email protected].

 

 

 

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You should note their suggestions about the useage of all materials , self etch primers , epoxy primers and rustproofing compounds. This noteable as this is somewhat changed from their original recommendations in past bulletins.

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I have used three cans of the eastwood internal frame coat on every possible opening I could get the nozzle into. The car has been sitting in a garage, in it's bare shell form for the better part of 8 months now. From what I can see in the hatch hinge pockets, it is holding up well. I will rehit every crevace, nook and cranny after the car is blasted and primed. I hope this holds up for the long haul, if not then it was only a minimal investment.

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Interesting article. I wonder what corrosion prevention compound they suggest? It makes sense that you would want to use something that doesn't require clean surfaces to adhere to since there's no telling what crap has built up in the sealed areas in the 40 years since my car was built. I believe the eastwood stuff is supposed to stick anything so it might be a good bet. I just want something long term. I've heard of people who keep their cars for years ending up doing the same rust repair over and over again and I don't want to end up as one of those guys.

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Pure Lanolin oil (sheeps wool oil) is another, very popular rust preventative here.

 

Smells better than fish oil for the week or so the smell hangs around before wearing off.

 

This is what I use. It's a really great rust preventive. It softens old tectyl/asphalt treatment, soaks into everywhere and soaks through the rust till undamaged metal. It's a really great and well tested product. It's used as the only preventive in ballast tanks in ships, oil rigs etc. Much recommended!

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I used to work with a guy who was big into sailboating. He said the boating mag did a story on corrosion prevention and found WD40 to be the best. Thats what I use.

 

For about 20 years I've relied on WELD THROUGH COATING for backside protection. Its a zinc based coating which bubbles up when heated red hot and permeates the voids and covers the oxidized metal where the welds are placed.....then cools and hardens. The spray is applied on the backside of patch panels and also on the interior if you can reach it. Let it set-up.....then weld. Works great.

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