Undercarriage Repair - Material & Adhesive VS Corrosion

[Bacon!]

I have an old SUV with undercarriage rot, but not very bad except in one area, presumably where the right rear wheel kicks up saltwater in winter, so I expect this area will continue to be pummeled by saltwater and road grime. It's between the wheel well and rear bumper. Pic below.

I know I could Do This Right, cut out every last trace of rust, weld in sheet steel, prime, paint, undercoat or goop it up with grease/etc to resist corrosion.

This area is normally inaccessible behind a trim panel, and it is a full framed vehicle. I checked the frame, it's fine. No load weight can be placed there, so the cheap side of me got to thinking, since this vehicle may not have too many more years left in it...

What if I cut out most of the rust, wire wheel down any remaining loose/crusty rust, coat any exterior facing rust, and slap a sheet of ~1/16" thick 5052 aluminum over it, held on with one of those newer fancy silane modified (silicone-polyurethane hybrid) adhesives like Loctite Max, which Loctite states is suitable for metal ?

Would bare 5052 aluminum be corrosion resistant enough that it would withstand salt spray for a few years? Would it help to put a coating of adhesive over it, exterior facing, instead of paint and primer since this isn't a visible area? It seems like that would resist road grime better than paint, but do I even need either if using 5052 instead of steel?

It might take a long time to fully cure between two sheets of metal, but it is water vapor curing and non-shrinking so I don't think it'll be a problem until then, held on with rivets or sheet metal screws.

I am aware of 3M Panel Bonding Epoxy, but it (+ applicator gun) is more expensive than I want for this project, as is the quantity of purpose specific metal bonding epoxy you find in those little 1/2 ounce shotgun syringe applicators. It would make more sense to weld it.

I also considered using 3M 5200 adhesive but after doing an eeny-meeny-miny-moe selection process at the hardware store, I came home with the Loctite Max instead. I've never used one of these new hybrid adhesives and wanted to see what they're like.

If it fails, I may end up going the weld steel/primer/paint/undercoating route, but wanted to know if anyone out there has done something similar and what their experiences were.

 

[harley jim]

Re: Undercarriage Repair - Material & Adhesive VS Corrosion

What year is the vehicle. Or a better question may be how many years did it take to rot out. Glue a piece of steel in there paint and undercoat it it will last the couple of years that you are looking for. Aluminum will react with the steel and salt( I know this because I tried it also) and it will rot out real quick. I had an 85 S10 Blazer that was my plow truck for years, I tried everything on it. By the time I gave it away I had replaced every panel except the roof at least once. Really glad I got out of the rust belt.

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[Bacon!]

It's a '98, but not daily driven for a few years. The rust is nowhere near bad except this one area, I mean sure the rocker panels and doglegs are getting there but were replaced with welded in, new steel a few years back so they are still in fair shape.

What grade of aluminum did you use? I have seen 5052 mentioned extensively as the Al of choice for marine environments, and I already had some, so there's that.

I doubt there will be any galvanic corrosion between it and the steel because it will have a fair layer of adhesive between the two, besides contact from a few rivets or screws that I can completely cover with adhesive too, so there's no air or moisture exposure if the whole panel is adhesive coated, *unless* road grime will abrade away the adhesive. I don't do much driving on gravel, hardly ever. I think I'm convinced to coat the entire panel instead of leaving it bare.

I don't have any scrap steel, so if I go that route and have to paint it too, I might as well have it welded, but all in, that's going to be at least 6X as expensive. Well, considering that this isn't visible, maybe a little less than that because I'm sure I have some rustoleum paint around here somewhere, but no aluminum primer. Is there any homebrew way to etch aluminum to get paint to stick better, an acid or something?

 

[condition001]

I used some pretty cheap panel epoxy on a similar hole. Rather than getting purpose made floor pans, I used an old aluminum street sign my grandfather had and glued it on the inside of the car. It was big enough to fill the whole floor well. I suspect you could do a similar repair relatively cheaply if you used something like this:

https://www.lowes.com/pd/Lexel-10-5-fl-oz-Clear-Paintable-Solvent-Caulk/4714985

It'd be cheap and ugly, and proceed at your own risk, but if you're looking strictly for function it might work...just make sure the metal is safe and secure enough to keep people in and stuff out


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[harley jim]

It's a '98, but not daily driven for a few years. The rust is nowhere near bad except this one area, I mean sure the rocker panels and doglegs are getting there but were replaced with welded in, new steel a few years back so they are still in fair shape.

What grade of aluminum did you use? I have seen 5052 mentioned extensively as the Al of choice for marine environments, and I already had some, so there's that.

I doubt there will be any galvanic corrosion between it and the steel because it will have a fair layer of adhesive between the two, besides contact from a few rivets or screws that I can completely cover with adhesive too, so there's no air or moisture exposure if the whole panel is adhesive coated, *unless* road grime will abrade away the adhesive. I don't do much driving on gravel, hardly ever. I think I'm convinced to coat the entire panel instead of leaving it bare.

I don't have any scrap steel, so if I go that route and have to paint it too, I might as well have it welded, but all in, that's going to be at least 6X as expensive. Well, considering that this isn't visible, maybe a little less than that because I'm sure I have some rustoleum paint around here somewhere, but no aluminum primer. Is there any homebrew way to etch aluminum to get paint to stick better, an acid or something?

It should last you long enough. You should paint all of the steel with a rust convertor and let it dry before you do anything that will slow the rust way down.
I don't remember what aluminum I used, it was most likely a piece of semi trailer roof since that was what I did back then for a living. Use what you got was my motto for too many years, it got me through!

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[Bacon!]

It's entirely behind a trim panel so just needs to stay water-tight while the rear wheel slings water up at it, and while not structurally important, it might flex a slight bit so the adhesive can't be brittle.

I might end up losing the storage bin built into the cover panel/trim so I can put a hatch on it to check whether it's leaking every so often. Really if I took the storage bin out, and left it an open hole where it was, it would expand the storage capacity there a lot, but then it would be subject to weight on it.

Seems like the thing to do next is play around with the adhesive, draw a few beads open and between some scrap metal to see how hard and strong it gets.

 

[condition001]

The lexel I mentioned is permanently flexible, so they might work well for you


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[99LeCouch]

Probably will work the same as JB-Weld and rivets in a piece of sheet steel. Although that repair lasted the 3 more years I had that car.

If you are riveting, the strength comes from that mechanical connection. The adhesive is to fill in the gaps and make sure the panel doesn't shift around. Rivets hate being exposed to shearing forces.

 

[harley jim]

Maybe panel adhesive and a couple pop rivets. Spray can undercoat outside to cushion impact from road debris.

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[Bacon!]

It's got to work better than JB-Weld, that stuff is pretty brittle. The rivets or screws are mainly going to be there to provide clamping force, and to hold it in place if it takes more days to fully cure in the middle than I wait before driving it again. Ironically this adhesive states you can speed up curing by spraying it with water but I just laid some beads of it and it looks thick enough to seal fine even if it takes a very long time to fully cure.

 

[harley jim]

Go for it. You can't take it back now

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[Bacon!]

^ haha, I figure the worst that'll happen is it just comes back apart then I weld it. I'm also interested in finding applications for this extra special $10/tube adhesive, or whether it's just designed to liberate me from an extra $5.

If it'll work in some apps where I usually use epoxy, that's still cheaper per oz than epoxy, at least at the rate I use it.

 

[Bacon!]

I had a picture linked/embedded, but now it is gone. What happened?
(time lapse) lol, NOW, the pic is back again.There's a glitch in the Matrix.........

imgur image host seems to be having problems, if I click this link, sometimes it works and other times it states "contains errors" and can't be displayed.

https://i.imgur.com/2ydjL8K.jpg

 

[bigguns69]

This isn't going to work for any significant length of time.

 

[Bretny]

Rust converter stuff didn't work if you dont prep the he'll out of the area. Nearly impossible in corners and samwitched metal.

What your proposing is basicly what this guy did. Yes this pic is real, he's a local guy and I have seen the vehicle on more than one occasion.

 

[56Mark]

I was coating a shower wall with aquadefense water proofing before installing ceramic tile last year. I got some of it on a 4" stainless taping knife I have and have since used it to spread thinset, sheetrock mud, etc and it has been scrubbed several time and there are still a few small spots of the green aquadefense on it. Every time I use it I wonder if it would be good to coat panels under cars? It is waterproof, kind of like hard rubber, and seams to hold up to abrasion since I haven't worn it off of the knife yet. I don't know if it is UV stable, but shouldn't matter under a car. It is about $50 a gallon. Thoughts?

 

[matt_i]

I think you could use 100% silicone out of a caulk tube to bond/seal the panel.

Even better would be the urethane that they use to glue windshields into the car. Its very weatherproof and very strong.

and if there are no fasteners and the dissimilar metals don't touch, then they can't galvanically corrode!

Your panel should be under minimal load seeing as the full-frame is taking care of this.

 

[Bacon!]

^ What I'm trying, that Loctite PL Max Adhesive, is a new fangled urethane with silicone chemically grafted on to both ends of the molecule somehow (if I understand it correctly, I'm not a chemist), is supposed to be the best of both worlds for urethane vs silicone, though maybe not as elastic as silicone. I'll know more about that once it finishes curing, looks like it's going to take every bit of the 24-48 hours (at 78F/50% RH) they estimate in the product Technical Data Sheet.

https://dm.henkel-dam.com/is/conten...esive-Plastic-Cartridge-9-fl-oz-2018-04-09pdf

 

[harley jim]

Bacon
How did it come out.
We need closure. Lol

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[Bacon!]

^ Unfortunately it's still a work in progress.

With winter setting in I've had a lot of projects I wanted to get done before it got colder, plus I had that test bead sitting to cure for 5 days but breaking it open, it still hadn't cured in the middle despite even putting a pan of water in front of it and using fan to blow more humidity its way. It is a water/humidity cure adhesive so that should have helped.

I waited a few more days and the bead cured inside so I did some strength testing of the test pieces of metal I'd joined with it. The perimeter was cured but once it got about 1-2mm into the mating surface of the metal, it had not cured at all.

Not good, I considered scrapping this and using epoxy but decided to fire off an email asking Loctite if they had any suggestions, since it is described as suitable for metal. I have not heard back from them.

Even with just the perimeter cured it wasn't really weak, had good shear force still and good adhesion so I'm still toying with the idea to try this adhesive, and also use it to coat the exposed metal instead of painting because it is a very tough surface once cured, sort of like hard plastic, but not brittle.

In the meantime I'd gathered up supplies and discovered I can't find my rivets and only had one cutoff wheel so I ordered another wheel and screws and misc Christmas shopping, etc which was a little shipping-delayed but is due to arrive any day now. I should've just bought these items at the local hardware store but I was on amazon and they had them so...

So that's where it stands, will probably get this done as soon as my screws and spare cutoff wheel arrive. Fortunately the weather is going to be unseasonably warm, in the 50F's temp for a few days and no rain or snow in the forecast.

 

[RPH]

I do automotive bonding for the industry. Look for an anaerobic type adhesive. These cure in the absence of oxygen. Exactly what you have between to the two pieces. Try an automotive paint store for structural adhesive, also Eastwood carries one. Done right the joint can be stronger than the metal.

 

[Bacon!]

^ I'm seeing Eastwoods' offerings listed just as epoxy, not anaerobic, but I already realized an epoxy would cure.

I've used epoxy for quite a few things in the past (besides autobody) but what turns me off about it is the roughly $10/oz price in small quantities. I want to find something that I can use as an epoxy replacement.

This repair seems like a good test candidate because it isn't structural, just needs to seal and resist minor gravel, ice/snow/rain kicked up by my rear wheel. I took the vehicle out in the rain the other day with that hole patched using a garbage bag and duct tape, out of curiosity to see if I could hear water thrown up at it and sure enough it is constantly sprayed by water, the result of having a truck chassis that doesn't have rear wheel well liners.

It makes me wonder if I should be wandering around a junkyard, looking for some wheel well liners that I could throw up in there. I could cut a slot in them for axle clearance if hauling a significant load caused a clearance problem. However this is an old vehicle and that is the sort of modification that probably should have been done when it was far newer, while now any repair only needs to last as long as the rest of the vehicle does.