View Full Version : How to slow rust? DIY undercoating? Ziebart? POR15? Oil mixture?

11-11-2009, 09:33 AM
Looking to do some type of undercoating on my 10 year old car. It's getting rusted pretty good.. I couldn't care less what the car looks like - I just want it to last me a few more years, if possible. Around here cars only last around 10-15 years before they're too rusted out to save. Frames crack, etc..

Going to replace the brake lines, and maybe some of the fuel lines. Getting pretty corroded.

When I was buying the brake lines, the counter guy told me to pick up some cans of undercoating and spray everything under the car.

I had never even thought of that before.. Didn't realize you could buy that stuff off the shelf.

So now I'm regretting not doing something sooner. Also, my other car which is jut a few years old is showing rust underneath.

I figure I'll test something out on my car, if it goes well, do it on the newer car too.

So, whats the best option? Particularly for a surface that's already rusted?
Should I buy the canned stuff off the shelves? Use regular Rustoleum paint?

What about POR 15?

Or how about some type of oily mixture? It wouldn't stop current rust, but would definitely slow progression - although it would need to be reapplied every winter once or twice.

Any suggestions?

11-11-2009, 09:50 AM
I would use something like POR 15 first to neutralize the rust and then spray with one of the durable truck bed sprays. It sprays thick and tough.

ironroad 9c1
11-11-2009, 09:54 AM
fact is there is so many nooks and cranny's you can't get to and even if you stop the rust on the outside, its still gonna rust in between stuff. if you don't like rust, move to a place they don't use salt.

11-11-2009, 10:09 AM
I've used POR 15 before and it's amazing stuff, except for when you get it on your skin...then not so amazing. The thing with POR 15 is that it needs to be applied directly to rusted or seasoned metal, so if the car already has some type of old undercoating, you would first need to remove that to get down to just the metal.

Great white
11-11-2009, 10:24 AM
If the rust is in to the point you need to replace brake and fuel lines, the car is most likely too far gone to save easily.

Take it to a shop and have them apply rust preventative coatings. This will pentrate into the seams and crevises to slow down the rust. It won't stop it, but it will slow it down.

You can't really do an acceptable job with spray cans and DIY stuff. Most shops will drill holes in the structure if there isn't an existing drain hole in order to get the coating into the inner areas where the rust problem really exists. Long tubes and special spray nozzles ensure proper coverage. If you can see rust on the outside, it's 5 times worse on the inside.

The idea is to coat the metal and prevent oxygen from getting to it. This stops/slows oxidation (rust).

DIY stuff is pretty much ineffective (vehicle tear downs and restors excluded). Not because the product is bad, but because most diy self-ers can't apply it properly. They can't get it inside panels and structures, and even if they do spray it in a hole it doesn't suffeciently cover the inside surface. Aerosol cans are best used for "touchups" through out the year. Also, by the time you achieved decent coverage with DIY stuff, you'll have spent more than if you had a shop do it becuase you'll need to buy more product due to improver application techniques. Unless, you go out and buy a compressor, spray guns and aplication nozzles. Even then, enviromental and cleanup issues are a biotch. Not to mention, you still don't have proper "techique"......

It also needs to be done once a year. Usually costs somewhere around 100 bucks. Worth it in the long run as it will add years of life to your vehicle.

As to the newer car, the sooner you start "undercoating", the longer it will last.....start now.

11-11-2009, 10:30 AM
Yea...I was adding up the POR stuff.. Gets real expensive..Plus the pain of getting the car high enough in the air to be able to apply it.

Maybe I'll call the local Ziebart place.. If anything, just to have it done to the newer car. Might not be worth doing on my car unless it was thoroughly prepped.

11-11-2009, 10:39 AM
Just off the phone with the local Ziebart place..

They're currently charging $260 to undercoat. They treat any rust spots first with a rust eliminator (for free during sale), then undercoat.

He said if I bring in both my cars - He'll only charge $225 each.

So $450 to have both cars done (plus tax)..

Money is a little tight right now.. So I'm hesitant..but if this helps our cars last a few more years, then obviously it's more than worth it.
If anything, maybe just to have the new car done - and write off my old car.

Any opinions?

11-11-2009, 10:52 AM
unfortunately the best time to undercoat a vehicle is the day you bought it.

But that doesnt mean that undercoating now is a waste.

POR is a great product, but trying to paint a frame (and do a decent job of it) while its on the vehicle is likely not going to work and be a waste of an expensive product.

While theres no doubt that you can paint the side rails of the frame etc, the real problem is in the areas that are next to impossable to reach with a paintbrush (like on top of the fuel tank or inside a door)

I recommend a product thats oil/wax/asphault or a mix of the above. I like ProForms Hybrid oil/wax in black Its a very sticky product, that will penetrate and seal all the nooks and crannys on your frame. The black colour will also cover the rust so the end result looks good.

Another good product is Krown, rust check ( or its clone "no drip oil" catid=28 ( but these are annual products. I dont like Ziebart

Fluid Film will also work but its $$$

Drill holes around the perimiter of the doors and cab with a unibit, about every 1.5 -2' or so and get a proper rustproofing gun with a hose. Spray these cavities with a oilbase or cavity wax product. Pay attention to the door sills and bottom of door area.

Remove your inner fenders and apply undercoating to those areas after cleaning out the old dirt.

Buy and install some rubber plugs for the holes you drilled.

Thats about it.

Might be alot easier to take it to a garage that does this, at least the first year, so you can see where they drilled the body for application. You can get Krown or Rust Check applied locally for $130 ish. ANd were in the middle of salt country on the ocean.

11-11-2009, 11:00 AM
Playing devil's advocate---
What are the odds that some coatings like discussed above could hold moisture in, causing more rust than letting it breathe?

11-11-2009, 12:31 PM
I have a friend that has a 1988 Dodge pickup truck, every year he takes it to a guy that sprays the under side with used motor oil, every nook and cranny. After 21 years and only 80,000+ miles the truck is almost flawless save for the normal paint chipping from various items shopping carts, bed scratches, door dings, etc. To bad something like that is probably illegal. Drips for 3 days then quits.

11-11-2009, 01:14 PM
this stuff is fantastic!
"non" toxic (tastes like crap though) and no fumes

11-11-2009, 01:54 PM
Waxoyl is used around the world to prevent chassis rot. Follow the directions for application for best results. Places you don't cover aren't protected. Your best bet on the old rust bucket is POR-15.

11-11-2009, 02:09 PM
I took autobody last year and the teacher said that Por 15 is great but have to remove any rust first. He said you could spray that stuff on and let dry and put the car in water for years and it would not hurt it

11-11-2009, 03:41 PM
Playing devil's advocate---
What are the odds that some coatings like discussed above could hold moisture in, causing more rust than letting it breathe?

Slim chances. The products i mentioned dont really skin up to seal in any moisture. The product should displace the water anyways. However i wouldnt apply it if the frame was soaked. Salt, on the other hand, i worry about. Thats why its best to coat the vehicle the very first year prior to the first salt, for the best long term protection.

Now a rubberized undercoating that forms a film could hold in water, i agree.

11-11-2009, 05:39 PM
Get yourself a "shutz" gun and do your own. You can get Rust Check (in shutz cans) at Canadian Tire or make your own juice (to re-fill). Bee's wax (toilet seals) disolved in Varsol then mixed with old ATF works very well. Vary the proportions to make it "creeping" or non. Play with the air pressure, you can make that gun "fog" or "squirt". Experiment with water to see how it performs. I use a siphon gun arrangement ( has a tube) that sucks right out of an orange juice jug. If you want something less gooey, thin down rolled roofing cement with Varsol and shoot with your Shootz. If replacing a fender etc I get the inside of it first before mounting.

11-11-2009, 06:08 PM
On all my old cars I used oil and or grease to protect the insides of the doors/1/4's ect. Cosmoline is 100% good too. Undercoat IMO will come off. The waxy/oily stuff is what you need.

ironroad 9c1
11-12-2009, 06:13 AM
Every car I have ever seen that was zbarted was rusted to hell. bought one on time had the passenger doors rusted slam up to the door handles, and zbart plugs in every door jamb. paid 150 bucks for it.

11-12-2009, 06:30 AM
Every car I have ever seen that was zbarted was rusted to hell. bought one on time had the passenger doors rusted slam up to the door handles, and zbart plugs in every door jamb. paid 150 bucks for it.

Probably because it was a one time thing. Rust proofing is not a shoot and forget it process, it needs regular maintenance along the way to be really effective. Especially inside doors,etc. as you have noted.