I have discovered four small areas of mild surface rust on the undercarriage my car that are just now beginning to eat through the factory paint. Two are along the rocker panels/floor panels on both driver and passenger sides of the car. The other two are under the rear fenders in the wheel wells where there is no factory undercoating and rocks have obviously taken the coating off. These are very mild surface rust spots, and the car is kept indoors and I try not to drive it in wet weather, and never in the winter. However, because road debris hits these places they will only get worse, and I feel the usual cheap paint won't do it, but I don't feel like undercoating the rockers.

I can kill this rust and have no future problems if I take care of it this summer. I am now not sure which product to use. I have used POR 15 before, but that was on a piece of rusted, bare metal. However, POR 15's directions and their customer service people have said that POR 15 does not like to stick to any kind of old coating, and will peel off and away from it. I simply plan to treat these specific spots rather than take the whole car apart and recoat the entire underside, as 95% of the factory original coating is perfectly fine still. I am afraid that when I brush the POR 15 over these areas, in the places it overlaps the old coating that is still good, it will just peel away and my rust problem will just return.

I have noticed on the banners for this site a product called "Rust Bullet" and have contacted them, and they claim their product will work just as well as POR 15, but also will adhere to the old factory coating as long as I scuff it up well. This sounds very ideal to me, but I have no experience with this product.

I am looking for some input from others on what product to use, will the peeling problem with POR 15 be as bad I am fearing (especially when topcoated)? I am also interested in the Rust Bullet product and would like some opinions from those who have used it, for similar situations or not. Also, any other product recommendations for this specific application would be appreciated.

 

I've been using Rust Encapsulator from Eastwood with good results.

 

it sounds like you could sand off the rust and just primer sealer, paint. For extra protection you can add in some rubberized undercoating to protect agains damage. With it being the underside I don't see a problem with the paint not matching up perfectly just tape the car off real good.

I do that from time to time put it up on jack stands and if I see any rust starting sand it off until I have clean metal tape off a square primer/sealer, and paint. But I live in GA so I don't have to deal with salt and I've only had to hit 2-3 spots over the years.

If your car isn't a show car Roll on bedliner is a great protector once you have taken care of the rust in rock chip prone areas of the floorpan.

 

Thanks for the replies. The salt here in Indiana isn't much of a problem for this car as it doesn't get driven in the winter if at all possible. However, many of the roads that I drive on with it have parts that are in poor repair and rocks and other debris are a problem. I'm not really worried too much about the paint matching, but I was hoping to just find a product I can brush on over the treated rust like POR 15, but will adhere to the old factory coating, and also be considerably tougher than just normal primer sealer and paint. I would like to avoid having to tape off the underside of the car and make a mini paint booth under it to protect my garage floor. I know that is probably the correct way to go about this, but that POR 15 I brushed over a bare iron wagon frame many years ago is still working great, and if I can get something like that to brush over these trouble spots and won't lift where it meets the old coating I will be very happy.

Rust Bullet's customer service claims their product can be brushed on, and will adhere to old coatings that are properly sanded. Has anyone ever actually used the product?

 

I prefer the SEM rust shield and find it sticks better than por 15.I added the gloss enhancer/hardner It protects it from fading and you can later scuff and topcoat w/undercoating if you like

 

Alright, I will look into the SEM rust shield. Any word on the Rust Bullet product or how POR 15 will work in this situation?

 

Any other suggestions, or reviews of the performance of Rust Bullet or POR 15 in this situation?