Rust Prevention – Do-It-Yourself Undercoating that WORKS!

For Sale, needs a little TLC
For Sale, needs a little TLC
For Sale, needs a little TLC

Crawl under your vehicle.  Look around at the suspension components, frame, bolts, drive shafts, everything metal.  If you’re lucky, it’s doesn’t look too bad right now.  But there’s probably rust here and there.  Surface rust creeping around, in the cracks, on the welds, on the castings.

The problem with rust is it’s oxidation of your iron and steel parts thanks to moisture and oxygen.  Oxidation is synonymous with corrosion, which literally means your metal is disappearing!  You people who live in the rust belt know what I’m talking about.  Long drawn out winters with roads covered in sodium chloride, otherwise known as nasty, vehicle eating, crushed rock salt carved out of underground mines.  This stuff is hell on the underside of your vehicle because it accelerates the rusting process.   Here’s the thing, I got bad news for you.  Right now the underside of your vehicle looks as good as it’s ever going to look.  That is unless you do something about it.

Rusty Panel Truck

Spend Hundreds or DIY for under $50

You can spend hundreds on a “professionally” applied undercoating.  But if you’re like me, you’d rather do-it-yourself if you can.  Well what if I told you that there is an effective, cheap, long term method of undercoating that not only looks good, but you can do yourself in one afternoon for about $40.  Think you’d be interested?

Ok, you’re thinking obviously I’ll be coating the underside with something, so what is it?  Gloss Black RustoleumBut hold on… it’s not just what but how.  You can easily paint anything that sits right in front of you.  Undercoating a vehicle is tricky because the things you need to paint are sometimes hard to reach.  The trick here is how you “coat” the underside with the Black Rustoleum paint.  Typically when you paint something, you’re painting it in a very even, light coat so the paint looks smooth.  Under the vehicle, it doesn’t matter!  So, I use a different method to apply the spray paint that not only coats everything in a thick coat of paint, but enables you to paint hard to reach places.

Here’s how to do it…..

Use Quality Paint, Not Bargain Brand Junk

First, you want to use a quality spray paint.  I’ve used lot of spray paints over the years and Gloss Black Rustoleum seems to be the most durable and rust resistant.  In my experience, this brand and color lasts the longest and in most cases it will match the underside just fine.  In fact, it will look great.  Next you want to take care to cover your vehicle with a sheet or something to prevent overspray from settling on your car’s paint job (if you’re worried about it).  Then of course, use a breathing apparatus to filter the air you breath.  Cover your eyes and hair and wear old clothes.  It will make a bit of a mess if it starts dripping or the overspray gets you.

red-tube-tip1Paint Delivery Nozzle

Much of the underside can be painted with the standard spray nozzle.  For hard to reach places, I’ve used a modified spray tip.  This works for the standard spray tip pictured to the right.  It won’t work with some tips, so check around for standard tips, which are easiest to modify.  Pop the spray nozzle off the can.  There’s a white tip where the paint comes out.  Pop that tip out with a utility knife.  Now you’ll see a hole.  In most cases that hole is just the right size to accept the red tub that you’ll find with spray solvents like carburetor cleaner or spray lubricant.  In some cases the red tube is thinner by just a little so in that case I’ll use a sharp all or pointy tip to slightly flare the red tube.  Now press that into the spray tip’s hole.  It should fit snug.  Now what you have is a tip that will be able to shoot paint at least a foot or two in a thick layer.  This is good enough to send paint into the tight spots under the chassis.  It also works well to shoot paint into the frame through the holes.

In some cases the tubed spray nozzles from carb cleaner or other spray products will fit right on top of a can of spray paint.  If so, keep them.  Before you do this job you’ll want a few of these in case they clog or the red tube pops out and goes flying somewhere out of reach.

Prep the Undersize

You’ll want the underside as clean and as possible.  Use a pressure washer to blast off the dirt.  Then let it dry for a few days.  If you have lots of oil and grease, I see no need to totally degrease the underside because grease is a rust inhibitor anyway and we’re not going for beauty here.  But if you can get down to metal, painting metal and exposed rust gives you the best bang for the buck.  Obviously surface dirt and caked on mud should be removed.  Painting dirt isn’t going to do anything except waste paint.

Getting Down to Painting

So then with your vehicle exterior paint covered, and your breathing mask on, start in the middle and work your way out.  Paint will drip so try not to get under the painted surfaces. Don’t park on a nice clean driveway either.  I like to park in the grass and lay on a sheet of cardboard to move around.

You may have to move the steering around to get into tight places like the knuckles.  Move the vehicle a little to rotate the drive shaft if your doing those too.

Plaster the whole underside.  Cover even the rusty parts.  The black Rustoleum will do a pretty good job of slowing the rust down and it does a great job of preventing rust on un-rusted metal.  I do the entire underside.  At 4 bucks a can, you can do the whole job with anywhere from 5 – 10 cans.  And you don’t have to do it all at once.  Later you can reapply when necessary.

Works Great on New and Nearly New Vehicles

There’s nothing worse than looking under your new vehicle and spying rust starting to appear here and there.  I’ve done this on several new vehicles and I can say without a doubt that it works great.  The newer the vehicle the better in this case because the surfaces are new, clean and free from rust.  If you do a new vehicle, it will prevent rust from starting.  You can even professionally undercoat it later over the paint if you want.

Does it work??

It should go without saying that the less rust the vehicle has to begin with the better.  This will not restore rusted out metal nor will it stop deeply rusted metal.  From experience, I can say absolutely this works.

The best example I can talk about is a 1992 Toyota 4×4 Pickup that I bought in 95.  It had sat most of the time before I bought it so it was very clean with no rust underneath.  Right after I purchased the truck, before it got all muddy, I completely painted the underside.  Even sprayed up into the fender wells where rust appears around the wheel well.  I drove the truck hard for 8 years.  It got muddy, it saw seasons of road salt, got smacked around offroad and I drove it over 100,000 miles.  My friend also had a 92 Toyota just like mine only he didn’t do any painting.  So I had these two trucks to compare years later.

Both trucks saw the same weather, same offroad action.   We both sold the trucks eventually.  I sold mine to another friend, he sold his to his mother.  So we saw the trucks for another 5 years or so.  12 years later the difference was amazing.  While his truck was badly rusted all over; some places right though the sheet metal, my old truck had minimal surface rust.  Nothing rusted out.  Much of the original paint still on the underside, frame and suspension.   My old truck was beat up, but rust wasn’t a problem.  Without a doubt the paint treatment worked.

The Take-Away

While you can’t prevent rust 100%, you can minimize it.  Untreated or poorly treated steel or iron will rust.   If you catch it early and coat it with something that will remain year after year, you delay or prevent rust.  While no daily driven vehicle will last forever, it’s a sad day when you realize your 4×4 is not mechanically dead but it’s falling apart thanks to rust.  For $50 and an afternoon you can do your vehicle a favor and keep it sound for the long term.  You can’t beat that deal.


Rusty JeepCall no chain strong, which holds one rusted link. Ella Wheeler Wilcox


  1. I bought a 1966 chevy truck from my son and it’s in pretty good shape but the frame has light rust all over it. So I have been wire brushing it, applying some Extend rust treatment (2 coats) and painting with black Rustoleum. I’m glad to hear someone else is doing this and that it works! Thank you!

  2. I can see why people would want to save money, but I think it would be best to choose a professional for a job like undercoating a truck. I like how you explain it step by step, but I don’t have all of those tools or the space to complete the job well. I’ve found in the long run doing it right the first time is what saves me money. Thanks for the great ideas.

  3. Simply wish to say your idea is a great one. After looking at undercoatings, this made so much more sense. I’ll be heading out to Lowes for a 6 pack of black Rustoluem!

  4. Generally I don’t learn much from post on blogs, but I would like to say that this write-up was like a light bulb good idea. Thanks, nice tip. Going to do this to my truck next weekend.

  5. I’ve always been of the mind that it’s easier to prevent rust than it is to stop it or remove it. Once that metal is gone, it’s gone! I’ve done the same thing with a few vehicles I’ve owned and every time I did this it worked for the most part. I used whatever paint i had so maybe a quality paint would have done a better job. Good article!

  6. Informative article, exactly what I needed for my bucket. I need to hold off the rust as long as possible. I don’t want to spend a lot but before I get it all muddy I want to coat it with something. Great idea! Thanks.

  7. Does this really work that well?? I mean come on, paint chips away, rust gets under paint. I’m thinking once it started rusting, your not going to stop it with just paint.

    • Yes, that’s true paint will chip off metal and metal will rust. But in my experience black Rustoleum adheres very well especially to nonrusted metal and resists creeping rust very well. I’ve also painted over mildly rusted metal that did not rust again. As I said, the Toyota truck I had did so much better than my brother-in-laws truck over the same years of exposure. Of course it’s not a bullet proof solution but it’s cheap and effective and will extend the life of the vehicles metal structure.

  8. Do you think i can get my BF to crawl under my Jeep and do this for me? LOL, I don’t want my baby to rust. Just got her and she’s rust free. I want 2 keep her that way 😀

  9. Hey, thanks for the tip! I bought a 2013 JK last year and the rust popping up irritates the shit out of me. I’m heading out to Walmart this evening for Black Rustoleum!

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