Car undercoating scratched

[GMFan]

Good evening,

I was under my car today performing an oil change and I noticed that one of the main frame beams underneath the car had a ~3-4 inch section where the undercoating for the frame was scraped off and pealing. I believe this happened when I bottomed out a few weeks turning up a STEEP road (heard a loud scrape).

A decent portion of the frame of those 3-4 inches is totally clean/bare metal. Thankfully no damage other than the black undercoating stuff. My concern is having the frame exposed to the elements.

Does anyone have any input on how to properly fix this? I am afraid of oxidation now. Even if I buy undercoating in a spray can and seal it back up is it already too late to avoid rust down the road?

Is sanding it down and painting it a better idea?

Thanks for any input.

 

[sciphi]

I'd degrease, prime, and re-coat with undercoating. A few weeks won't do much, especially with this mild winter we've been having.

 

[addyguy]

I'd be inclined to go to the dealership and see if they will touch it up for you.

That way you have the EXACT same stuff on there....

 

[Corvette Owner]

Is this extra undercoating that you paid to have applied?

The reason I ask this is that most new cars (assuming this is your 2011 car) use good materials from the factory and are covered for usually a 72 month rust through warranty.

Also, the frame is the thickest metal of the undercarriage, so rust through is less of a problem here.

If you paid for undercoating, see if they will touch up. If this is factory, you could touch it up yourself. Wash area and do an alcohol.

In any case, I don't see much of a problem, even if you let it as is.

 

[JHZR2]

Ive had facory coatings that were scratched. Ive cleaned/sanded, and then tried different things. Truck bedcoating doesnt stick well, and gets too hard. The standard spray undercoating (e.g. 3M products) can be good, but arent recommended for where rocks can hit - the have other products for that, but they are much harder to find.

I ended up going with a waxy protective coating that I can easily touch up myself. A product like Amsoil HD metal protector, or one of the other equivalents to this would be my recommendation. Just build it up slowly over time.

 

[GMFan]

The undercoating is the standard stuff applied at the factory. No extra undercoating was purchased.

If I go the route of using the spray on 3M rubberized undercoating, how should I go about prepping the area besides sand and degrease? Any other steps to "prime" it for better application?

 

[JHZR2]

Ive always just done that, and it tends to work and stick well forever.

I have heard that the spray undercoating stuff can tend to collect water underneath and cause rust underneath. So Id be careful with it. That's why I like the idea of keeping after it with the waxy stuff. Especially since the PDSs for the 3m stuff recommends not being used in places where rocks can hit...

 

[antiqueshell]

Most likely it is a hard rubber coating if factory, the best compatible product off the shelf probably would be Wurth Underbody Seal.

 

[GMFan]

Would there be any reason why I shouldn't just use black spray paint after a good sanding and de-greasing?

 

[eljefino]

I would use undercoating or something tough and glossy like POR15 if you have to use paint. Regular spray paint won't seal against the torrent of water and abrasives that wash underneath.

I would also put a heat lamp on it while it cures, and for that matter, before you apply it. I've done undercoating in the winter ish weather that didn't cure right and didn't stick.

Beware flammable vapors.

The undercoating the dealer will put on won't be what the factory used. Factory probably had some assembly line related issues that needed quick drying stuff or had another fancy technique like baking in an oven, two part epoxy, who knows. Plus who knows what environmental or health safety laws affected the formula between when the car was built and now. And they'll pay the minimum wage drone to just hose your car down with 3M stuff like you could do yourself, then you wonder if they prepped it right.

 

[mechtech2]

Spray an undercoating on it. Repeat after a few days.
And You will have much left in the can for future scratches.