One of our friends is asking for some help with an old van that they picked up to haul stuff for their new home. They are doing a lot of remodeling and cleanup and thought picking up an old van would be cheaper than delivery costs or renting on the weekends. The problem is the van has a lot of underbody surface rust.
At this point its not to where they will need to do some metal replacement but if something isn’t done the next couple years could cause enough rust that repairs would cost more than the van cost. They knew the vehicle wasn’t a long term keeper but they want to do something that will let them keep it a bit longer.
In the Northeast or anywhere that they use a lot of road salt in the winter this problem is a real one. Cars and all vehicles will have a shorter lifespan. Its a really pitiful situation because there are some car brands that are well know to rust apart just about the time that the warranty runs out and they aren’t addressing the problem.
How To Protect Your Cars Rusty Underbody
Because rust will form in areas that are very difficult to get to the ability to treat the metal is limited. One product that does work well is Phosphoric Acid and manufacturers bottle this stuff up and sell it as Rust Remover or Rust Converter.
If you can its always best to try to remove the rust mechanically. This means the use of wire brushes or wire wheels on griders. You can also use a less abrasive blasting method like Dustless Blasting and for frames and heavy parts you can just sand blast the areas. Not everyone has access to blasting equipment so a good dust mask and eye protection and a braided wire wheel on a 4 inch grinder is going to be your friend.
You want to go over all of your suspension parts and brake backing plates. Hit the area with a pressure washer and degreaser to remove the grease and then go over it with a wire wheel.
When you have got as much as you can you can then treat the area with rust converter. Applying it is easy with a small garden sprayer or a brush. Make sure that you get it in your frame openings the best you can and between panels. Anywhere that there is rust you should treat with the converter.
Rust converter is an acid that reacts with the rust and turns it into a paintable surface however if there is a lot of buildup you will want to rinse it off before you primer and paint it.
Painting Over Rust Converted Or Bare Metal
You can use synthetic enamel to paint your vehicle and touchup paint from the auto store is enough for an old vehicle to hit some rust spots.
There are other paints and coatings that you might want to consider. Some are marketed just for this purpose however I would not expect results that are extremely better than basic synthetic enamel.
Another option is that you can normally get single stage black factory pack paint with reducer and hardener at around $100 for a gallon. If you have a vehicle that you are really restoring I would go with this or go with a color matched single stage acrylic enamel. The problem is you have to be much more careful about removing the rust before you paint acrylic enamel. In the end it will last many times longer.
Undercoating products are hit and miss. Most people say that they will get hard and crack and then moisture will get trapped between the undercoating and the metal. This can increase or quicken the rusting process.
Final Note
Having friends that live in some of the worst snow areas of the northeast another method is to use a rust converter and then simply spray a thin oil on the underside of your vehicle. If you are only expecting to keep your vehicle another season this might be ok and the oil will cause a film that will dry to some extent.
Personally if I was doing a quick and dirty protection job I would spray the rust converter on a few times and then use some cheap black spray can paint. It will last a few years and you won’t be looking at costly rust repairs immediately.