Underbody Rust

I Have a xj 90 limited and theres a little problem theres a lot rust under the body, do you have any idea or opinin what can i do to stop it, i found this on the net http://www.duplicolor.com/products/rustfix.html you think this will work

Depends on how bad the rust is, if it's really bad on the floor panels then the best route is to cut the rusted parts out and replace with new sheet metal, prime, paint or undercoat. If it is just surface rust then sand it off, coat with por15, paint or undercoat. POR15 is UV sensitive so it needs a top coat after you get it on...

I think I've asked this before, but this is another good chance. Has anyone actually used RustBullet of Texas? Their website is impressive--mainly their list of customers. Its advantage over Ospho or POR is that it needs no topcoat. Though a second coat is recommended for max. protection, it's certainly more convenient to not have to buy two different products & I'd think there would be less worry about not getting everything completely 2nd-coated..

Here's the stupid question that concerns me most: whatever product is used, can one safely spray it on the whole underbody? Is it going to gum something up, seal things in place that one doesn't WANT sealed in place? Do certain things have to be masked off before spraying? In other words, is this a job for someone who knows what he's doing & not for an energetic novice?

Figure out what type of rust it is, surface rust or rot. Trouble with much of the coatings is, once you get it on, you really don´t know whats going on underneath. I´ve never used POR 15, but have tried a series of rust magic elixers over the years. All to often, after a few years, the coating developes blisters and what´s underneath is rot.
I religiously wash my underbody, salt and mud are moisture traps that start rot.
Undercoating, gavanized parts, such as brake lines has rarley worked out well and gets int he way during inspections.
The best system I´ve found is to seriously clean and coat, a couple of fender wells in the spring, then a couple more in the fall, then move on to another part (gas tank area and rear) the next year. Pretty much get the whole XJ every 4 or 5 years.
I´ve had pretty good luck with Toreson undercoating primer (made by the same people that do Loc Tite), it´s some kind of resin, that is somewhat transparent and can be sanded off, if you need to weld.

I have underbody rot in 2 small spots ABOVE my cat converter. It is through all the way to the soft liner. Can you weld a plate to the frame and across or do I have to clean to bare metal on the underbody and put a plate there??

Eagle... any ideas??

Rob Pettey

Rocketman said:

I have underbody rot in 2 small spots ABOVE my cat converter. It is through all the way to the soft liner. Can you weld a plate to the frame and across or do I have to clean to bare metal on the underbody and put a plate there??

Eagle... any ideas??

Rob Pettey

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The hot ticket for controlling underbody rot over the cat is to put a heat shield between the CAT and the bottom side of the of the floorpan. The neatest way I have heard of doing this is to buy one of those "airbake" hollow cookie sheets available at kitchen stores. This is then attached to the underside of the floorpan with insulators to space it off the floor by about 3/4 of an inch.

The idea is to keep the intense heat of the cat from oxidizing the steel floorpan by creating a thermal barrier.

Of course, if the floorpan is all rotted out, that would have to be repaired before this improvement can be instituted.

i've got rot in two places first is a small (about 3in long by 1/2in wide) area just forward of where the crossmember is which should be easy enough to fix with an angle grinder, some sheet metal and a mig welder... but the second spot is a little different its in the front drivers side wheel well (just behind the plastic "armor") the rot goes clean through the thin single thickness sheet metal (silver dollar size) right after the bend upwards into the wheel well and goes into the double or triple thick portion of sheet, whats the best way to fix this? grind it out and weld in more sheet metal?... i found this all when i was wire brushing and replacing undercoat below my heep... imagine my surprise when i turned my heep into a fred flintstone 'mobile :helpme:

Rocketman said:

I have underbody rot in 2 small spots ABOVE my cat converter. It is through all the way to the soft liner. Can you weld a plate to the frame and across or do I have to clean to bare metal on the underbody and put a plate there??

Eagle... any ideas??

Rob Pettey

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Welding a plate to the frame and across just creates another place for dirt and moisture to collect, causing yet more rust and rot. The right way to fix it is to cut out the rusted metal to solid material, then weld in a patch of new steel. If you aren't a welder and the holes are truly SMALL, you can use pop rivets or sheet metal screws. Be advised, however, that what appears to be a small hole may in fact be very large when you finish wire brushing and cutting out all the less than solid metal. I had to replace the entire floor on the drivers side of my MJ. Fortunately for me, a friend's father is a professional welder, because I could not have done the job myself.

Churchlady -- OPR-15 and OSPHO are very different products. POR stands for "Paint Over Rust" (or so I have been told). It is a rust-killing primer. OSPHO is a mild phosphoric acid solution, nothing more. I have two gallons of it in my basement -- it's good for stopping rust, and the remaining black oxide is neutralized and won't continue to rust. However, any solid metal adjacent WILL continue to be susceptible to rust. OSPHO isn't a paint or a primer, so after the OSPHO has dried the surface should be washed off with PREP-SOL (or equal), primed, and painted.

Depending on the amount of rust you can stop it from getting worse with POR 15. I don't reccomend painting over rust but if you have to this is the best stuff. When I was on a ship in the Navy our biggest problem was rust and POR 15 is the only thing I've used that will permantly stop rust.

http://www.POR15.com

They make a specific product for undercoats.

I use Zero Rust, safer than POR-15 to use. I am the process of replacing/repairing my entire floorpan(s).. I have been sandblasting the "frame" rails and all other metal beneath my XJ. They will now receive a couple of coats Zero Rust and then bedliner.
You do not need to top coat ZR, but if you want it does come in colors and a clear. Have had very good luck with it.

How is it safer to use?

Chemically safer.Actually let me qualify that....one of the state garages here use ZR, I asked them why not POR-15 and they said because of the chemical make up of ZR was safer than POR. I have not compared the MSDS on either of the products but I know that ZR does not contain isocyanates and POR does.
I have used both products and I prefer ZR, JMHO

dizzymac said:

Chemically safer.Actually let me qualify that....one of the state garages here use ZR, I asked them why not POR-15 and they said because of the chemical make up of ZR was safer than POR. I have not compared the MSDS on either of the products but I know that ZR does not contain isocyanates and POR does.
I have used both products and I prefer ZR, JMHO

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Thanks