Hi, I'm having the floor of my W123 replaced. My country uses road salt, so the underside of the car had a lot of patches (and some of the patches had their own patches). Anyway, I managed to buy some metal panels tfor the underside, hopefully they will last longer than the patches.
The question is, how to prevent the new metal from rusting again, especially in winter with the salt. The mechanic usually uses something caled "body 999" to seal welds and such, but said it would be very expensive to coat the whole underside with it (though I would probably be OK with it, if it meant that the new panels would stay rust-free for a long time).
In my country people usually cover the underside of the car with pitch , but there probably are better materials.
What do the factories use to rust-proof the underside? Is it a type of rubber-based coating like the "body 999"? I saw some youtube videos where they said that rubber-based coating would accelerate rust. Is that true? Why does anybody use it then?
Hy!
I have no experience with rubber based sealers, like Body 999.
For rust proofing, I suggest you follow these steps:
First make sure there is no any sign of rust or corrosion. If you see any, remove it so it will not spread. If you don't or cannot remove it, rust protection will only slow down its spreading.
Then you apply a primer color for metal or a rust converter. I use the last one.
Then you apply corrosion protection based either on bitumen or oil (Krown oil for example). If you make it well, bitumen lasts longer. Oil has to be reapplied every two years. Then you just monitor in what shape it is and reapply it if needed and, if you want, you can wash it as a preventive maintenance (bitumen, not oil).
I'm familiar Toyota uses some kind of rust protection by sinking the chasis in a liquid. I also noticed some bitumen based protection.
Good luck!
Modern car manufacturers use a coating of zinc on the steel - galvanizing it. Back in the 60's, I lived in the US Midwest, and we would regularly see 5 year old cars that were worthless because of salt-induced rust.
The main problem with coatings to prevent rust is that it's VERY hard not to put some of the coating on top of rust. Coating covered rusty metal will continue to rust.
Do not use rubberized undercoating. It will make the rust worse.
I recently look at a brand new Mercedes Sprinter, and they used some kind of amber waxy substance. It looked like Cosmoline.
I have found Fluid Film to work well in retarding corrosion. It does need to be reapplied periodically. I do that once a year in the fall, applying with an air gun to get good coverage. (I buy the gallon cans. The small spray cans are only good for spot coverage of small areas.)
how much $$ do you spend on it yearly?
A gallon can is enough for 2-3 applications depending on the size of the vehicle and costs about $40. So I usually go through one of those each season.
https://www.theruststore.com/Fluid-Film-1-Gallon-Can-P181C67.aspx
That's not terrible. How long have you been using it? Maybe you take a photo of the undercarriage next time you're there.
I've been using it for about 6-7 years now, on old vehicles that already had some rust. There's been no noticeable deterioration since then. I'll have to see about getting a photo or two. (There are some similar products out there such Waxoyl and Krown but I haven't tried those.)