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Best Rust Proofing Service: Krown, Rust Check or Corrosion Free?

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Updated August 3, 2023

Rust proofing your vehicle is one of the easiest ways to invest in its longevity and value by slowing down or inhibiting corrosion of body panels, frames, brackets, linkages, electrical fittings, plug-ins, wires and connectors and other parts.

Here are the options available and how they stack up against each other. This guide compares the companies, formulas, application processes and warranties of the most popular services.

While they will not reverse rust that has already occurred, they will slow and control its spread.

The best rust proofing options are those that are annual oil-based sprays that are environmentally friendly, non-drying, won’t clog drain holes and have self-healing/creeping properties:

ServiceCostApplication TimeDrip?Holes drilled?
Rust Check$1201 hourOccasional drippingYes, but optional
Krown$12045 min to an hour24-48 hours of minor drippingYes, but optional
Corrosion Free$1501 hourDrip-freeNo

Study by Department of Defense Research and Development

A 2006 study conducted by the Department of Defense Research and Development to review corrosion control and prevention on army vehicles, and was prompted due to the rising costs of repair the government was incurring, along with choosing the best solution to increase service life and functionality of the vehicles.

It tested the following rust corrosion preventive compounds (CPCs):

It found:

In a benign environment, the CPCs tested, performed equally well. In more severe environments, the choice of CPC is important. of the CPCs tested, Corrosion Free, Formula 3000 showed the most corrosion inhibition.

Review of Corrosion Control Programs and Research Activities for Army Vehicles (2006)

All 3 scored similarly in benign environments, with Corrosion Free scoring slightly higher. However, in severe urban and industrial conditions, tested in St. Jean Baptiste, Montreal, Quebec, (Corrosion Free was the winner with a 90% effective rating for inhibiting rust, followed by Krown with 70% and Rust Check with 40%.

Percent inhibition of corrosion of CPCs. Green is at CFB Trenton (rural/moderate) and Red is at St. Jean Baptiste (urban/severe). (higher is better)
Average darkening index for the nine CPCs at four locations. (lower is better)

1999 tests by Quality Engineering Test Establishment (QETE) evaluating Rust Check, Krown T-040, Fluid Film and others for application on Canadian Army vehicles found that only Krown T-40 met all the property limits.

The tests evaluated creep, penetration, water displacement, lubrication, wear resistance, compatibility with the paint used on the vehicles, flash point, and dielectric breakdown voltage.

Technician skill and attention is key

A tool is only as effective as its user.

Choosing a great product means nothing if it isn’t applied properly by a trained professional. The effectiveness of a top rated solutions like Corrosion Free can be negated by clumsy, bored, tired or uncaring service technicians. Do your research and find highly recommended dealers in your area.

If you can’t find a great dealer for the product you want, it could be worth considering your second or third choice to guarantee it is applied properly and done right the first time.

I’d rather get the service done by a shop with technicians that receive regular training and perform dozens, if not hundreds of rust proofing jobs every week than one that receives infrequent training and does it a few times a week a secondary service (I’m looking at you Canadian Tire).

Best overall – Krown

  • Founded: 1986
  • Locations: Over 250 locations in Canada & the USA
  • Frequency: Annually
  • Duration: 1 hour


Krown is a Canadian-owned and operated co-operative headquartered in Schomberg, Ontario. It was formed in 1986 as Krown Rust Control System by a group of dissatisfied former employees of Rust Check joined by 35 Rust Check dealers in Ontario and BC. Freeman Young was one of these employees and is the President and Co-founder of the company.

Krown is recommended across Ontario by CAA and members can save $10 on Krown rust control application and 20% off Krown merchandise. It is also recommended by the Automobile Protection Association (APA).

Each Krown location is owned by a small business owner who has an equal say in the direction of the parent company and is not a franchisee.

Unlike the franchising model used by other companies, dealers are not charged royalties, deadlines, quotas. After charging initial investment fees, Krown becomes a chemical distribution company to its dealers.


Their formula is a light oil (petroleum) based liquid with rust inhibitor additives. It contains no solvents, no toxins, no VOC’s (volatile organic compounds) and is non-flammable, non-reactive, non-corrosive, and is not WHMIS controlled. Over 80% of the ingredients in the Krown product are made up of re-refined materials and additives. It is dielectric, meaning it does not conduct electricity and can safely be applied to batteries, wiring and connections.

Krown Rust Protection & Lubricant (formerly called T40), which they describe as the “best rust protection on the market” is available on Amazon in an aerosol can for touchups and DIY applications. It is a flammable aerosol as it includes isobutane and propane. It is to be kept out of drains, sewers, ditches, and waterways.


Before the formula is applied, they apply silicone (eg. Silicone Lubricant from Canadian Tire, Home Depot) to exposed rubber door and body seals to protect them from it. This is because it will cause natural rubber weather-stripping and gaskets to swell. The rubber components in the engine bay and on the undercarriage are made of synthetic rubber/plastic designed to withstand contact with chemicals.

The formula is is atomized with compressed air to create a fine mist and applied using a wand to spray it onto the entire underside the vehicle. It forms a chemical bond with the metal, displacing any existing moisture and lifting it off and out of seams.

Inconspicuous access holes are drilled in the door jambs, rockers, etc. so they can snake the spray wand in and spray the solution around the inside of the panels, where salty water can accumulate after it trickles in past rubber window seals – particularly if the drainage holes become blocked by debris.

The holes are then greased to protect the exposed metal from corrosion and plugged to prevent water and air from entering.

Finally, the vehicle is then washed with special soap to remove excess product from painted surfaces and windows.

One downside of Krown is the dripping that occurs after application. The solution needs to be thin enough to get everywhere that water can, and once it has worked its way into the tightest welded seams of your vehicle, the excess product drips off. The majority of the dripping happens in the first 24-48 hours after application. The marks on asphalt driveways will go away after a couple of weeks. Krown provides a cleaning product to remove stains from concrete or interlocking brick.

Krown technicians go to training seminars every year to learn how to spray as well as to receive updates on the new techniques for current vehicles. Training videos demonstrating the proper application process are also used to ensure that the correct procedure for application is performed on all vehicles.


Krown’s warranty applies to new and used vehicles that you have treated since pretty much day one. New vehicles have to be less than 1 year old from the manufacturing date and Krown in applied no more than 6 months after the vehicle is purchased. Their used vehicle warranty is for vehicles less than 3 years old and Krown is applied less than 24 months after the vehicle is purchased.

The warranty continues to apply indefinitely as long as the service is applied annually plus or minus 30 days of the anniversary date and will repair or replace the following if they rust through, up to the current cash value of the vehicle:

  • Body panels below window line
  • Seams and crevices
  • Floor/rocker panels

It does not cover surface rust or rust on:

  • Roofs
  • Rusting caused by stone chips
  • Nicks, scratches, chips
  • Rusting of foam-filled areas
  • Front fenders without fender liners, all mechanical parts, paint peeling/blistering/bubbling along seams, crevices and body panels that are not perforated.

Their warranty is transferable to a new owner when the vehicle is sold.

See: Full warranty

Best for severe environments – Corrosion Free

  • Founded: 1995
  • Locations: Across Canada
  • Frequency: Every 18 months
  • Duration: 1 hour


Corrosion Free is a Canadian company and family business incorporated (OCN 1165095) in 1996 and headquartered in Caledon, Ontario L7C 2K1. Stephen Del Grande is listed as co-owner.

Independent auto repair shops can apply to become a dealer and service provider of Corrosion Free. The company sells their dealers the necessary spray gun equipment and Formula 3000 and makes in-person training and support available to them. Canadian Tire is a dealer of their products, but I’d recommend trying to find an independent shop to do the application.


Their Formula 3000 with CSC850 is made of lubricating oils (reportedly food grade mineral oils), metal conditioner and organic corrosion inhibitors in the form of a viscous, clear gel (from the process of polarizing the oil) that is practically odorless. It is safe for application on metal, vinyl and plastics.

It is thin enough to creep into seams and push away moisture, but has a static polarity to it that allows it to bond to metal and not drip off.

It is transparent, drip-free, solvent-free, non-toxic and safe for rubber, wiring and plastic harnesses. It is not subject to TSCA or controlled by WHMIS as it is is not flammable. However, its Safety Data Sheet still states it should not be released into the environment and should not be allowed to enter drains, water courses or the soil.


It is applied using a spray machine that works like a paint gun to spray a fine mist of a vaseline-like substance onto the underside of a vehicle. Then, a fogger gun is used to atomize the product and coat hard-to-reach areas like open holes, frames, fenders and panels.

Existing drain holes, vents, and factory access holes are used to apply the product to the inside of door and frame panels. However, some vehicles may require a hole to be drilled to access hidden cavities. The ‘E’ or Essential package does not include drilling holes, but the ‘C’ or Complete package will drill a hole if necessary to access additional cavities.


Corrosion Free has the best warranty as it is the only one that doesn’t require a rust-through hole in a panel to cover repairs.

Applies to vehicles newer than 3 model years old that are rust free at the time of treatment and continues to apply indefinitely as long as the vehicle is retreated every 18 months with the same package.

They will pay for the repair or replacement of body panels or structural frame members weakened by corrosion or rust. It also covers the roof and floor pans of the vehicle, as well as:

  • Fuel tanks
  • Fuel lines
  • Hydraulic brake lines
  • Emergency brake cables

It excludes all other parts, including:

  • Paint peeling, blistering or bubbling
  • Mechanical parts: oil pans, AC, power steering lines, window trim, etc.

It is transferrable to a new owner and has no mileage restriction.

Full warranty details

Rust Check

  • Founded: 1972
  • Locations: 270 centers worldwide
  • Frequency: Annually
  • Duration: 1 hour


Rust Check is a Canadian company headquartered in Mississauga, ON.


Their formulas Rust Check and Coat & Protect are electro-chemical compounds made of highly refined (Purified) mineral oils with corrosion inhibitor additives that are thin enough to creep into seams and crevices and non-drying to stay mobile. Rust Check is a light liquid, while Coat & Protect is a thicker version with the same properties used as the undercoating. They are not classified as toxic or flammable so are not WHMIS controlled and are exempt from Transportation of Dangerous Goods (TDG) Regulations.

Coat & Protect’s Safety Data Sheet states it is a flammable aerosol that includes isobutane and propane, Calcium Carbonate and Calcium petroleum sulfonate and is to be kept out of drains, sewers, ditches, and waterways.


Similar to Krown, Coat & Protect is applied to the the underside of a vehicle using a spray gun as a highly concentrated, pressurized mist that coats surfaces with corrosion inhibitors that bond to metal and displace moisture. Rust Check is fogged into the inside of the side panels. It is not applied on the floor boards inside the car under the carpet.

It then acts as a barrier, preventing water and oxygen molecules from reaching the metal, preventing rust from developing.

A few 1/2″ holes may be required in order to access the inside panels the design of the vehicle has not allowed for. Occasional dripping of excess liquid will occur after application.


Applies to all rust-free vehicles less than one model year old, and qualifying vehicles newer than 3 model years.

It is a 1 year warranty that renews as long as you get an annual rust proofing service done, making it “lifetime”.

Their warranty pays for repairs of original body panels from the window sills down that have rusted through from the inside out in accordance with the Warranty Certificate It is transferrable to new owners and has no mileage restrictions.

It does not cover:

  • Areas above the window line
  • Surface and/or cosmetic rust
  • Mechanically related (exhaust, gas tank, etc.)
  • Floor boards
  • Weather strips and rubbers
  • Bumpers and chrome areas

Partial warranty detailsWarranty details

Can you do rust proofing yourself?

Yes, you can buy aerosol cans of one of the top products and apply solution directly to areas where you see rust has started or to touch-up a previous application:

You can also get a spray gun from Canadian manufacturer Lemmer on Amazon and follow Canadian YouTuber 4DIYers’ excellent video to apply it yourself:

However, a professional service will likely be quicker, more complete and more precise, and prevent any from getting where it shouldn’t, such as on the brakes, exhaust and drive belts.

What rust proofing options should you avoid?

Traditional tar, oil or wax based sealants

Black tar like or waxy coatings covers over the areas that are susceptible to rust with a tar based product, and on first glance looks like a strong, long-lasting solution to protecting the underside of your new car. One example of this kind is Ziebart’s Z-Gard® “permanent” solution, which is a thick, asphalt-based sealant that comes with a 10-year warranty.

This type of rust proofing may be offered by dealerships as an add-on when purchasing a car:

While a decent short term solution, these hard, black “vulcanized”, “rubberized” or “pliable” “permanent” undercoating products are an old technology and will eventually wear, crack and become damaged (see this video). When this happens, it allows oxygen and moisture to get to the metal and may clog drain holes. This can trap moisture between the coating and the metal, accelerating the corrosion process.

These products also don’t have the ability to penetrate into the hard to reach seams and crevices where rust is more likely to form.

According to a 2009 Toyota tech tip, “rubberized” undercoatings may shrink and crack over time and tend to trap moisture and salt against components actually promoting corrosion.

Electronic rust inhibitors

This type of rust proofing is most often offered by dealerships as an add-on when purchasing a car:

Electronic rust inhibitors vary in price depending on who does the installation. Companies such as Canadian Tire charge as low as $300, while a dealership may charge from $500 to $1000.

These units connect to a vehicle’s battery and send weak electrical currents through the metal frame of the car and connecting it to a more easily corroded “sacrificial metal” to prevent the electrochemical reaction of corrosion known as in a process known as Impressed Current Cathodic Protection (ICCP).

ICCP is a proven technique to slow and inhibit rust on submerged structures: hot water tanks, boats, pipelines, bridges, concrete etc.

However, while it might sound like a high-tech, modern solution, the products offering this technology have repeatedly been shown to be ineffective when used on vehicles time and time again:

  • Corrosion control professionals find they do not work.
  • The APA does not recommend electronic rust protection.
  • The tech tip warns that induced voltages may interfere with new vehicles’ control and operating systems. It has the potential to drain the vehicle’s battery and may result in premature battery failure due to a parasitic draw.
  • In 1996 the FTC banned the sale of “Rust Buster” and “Rust Evader” and had them pay restitution to their customers.
  • In 2015, Consumer Protection of Western Australia found that the MotorOne computerised electronic corrosion inhibitor did not work as claimed.
  • In 2007, the Competition Bureau investigated and banned several companies from selling the devices, since the performance claims about a product must be proven based on adequate and proper tests according to Section 74.01(1) (b) of the Competition Act and the companies were not able to support their claims.

However, the Competition Bureau ended its investigations into 2 the companies selling 2 products: Auto Saver and CAP Final Coat after ISO-certified lab by a US-based company showed sufficient evidence of the slowdown of rust formation in the report Substantiation Testing on Automotive Impressed Current Protection (ICP) Corrosion Protection System and the peer reviewed Electromagnetic induction corrosion control technology (EICCT).

Should I wash my car after rustproofing?

No, it is not suggested to wash your car after getting rustproofing as it can remove the applied formula. Avoid using soap and detergents for at least 48 hours after the service, and wait at least a week before washing the underside of your vehicle to allow the product to harden.


  • “THE CONSUMER GAME Rustproofing warranties affected by dealer rivalry.” Globe & Mail [Toronto, Canada], 23 May 1986, p. A18. Gale Academic OneFile, link.gale.com/apps/doc/A165434606/AONE?u=googlescholar&sid=sitemap&xid=72b29407. Accessed 29 July 2023.

Over to you

Which solution is best for you? Have you had good or bad experiences with any products or dealers in the past? Let us know by leaving a comment below!

Know a product that you think should be included?

About the author

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Alex Wideman
Alex Wideman is a consumer rights advocate, serial entrepreneur and the editor-in-chief of Cansumer. He has a bachelor's degree in electrical engineering from Queen's University. He is passionate about helping others save time and money and has been creating consumer-focused online resources for over 10 years. More about Cansumer Read more

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  1. The article suggest avoiding ‘non oil based’ products. yet, it rates Corrosion Free as most effective rust inhibitor. (Corrosion Free is non oil based). Can anyone clarify why they rate CF as best?

  2. How well the product is applied is by FAR the most important factor. I took my truck to a Krown shop on the advice of a mechanic who was friends with the owner. They had a glass window so you could watch the technicians. Great! But they were busy, and putting multiple vehicles through with more than one technician, assembly line style. I saw that one fender of the truck had been completely missed, and asked that the truck be taken back in and resprayed. The owner came out and said he did that fender himself, so it was done. I said come outside and look at it; it is completely dry. He refused and started yelling that he had done it. I got angry and raised my voice as well, and insisted he come check out to check the truck and respray it. Owner screamed at me to get out of his shop or he would call the cops, with hand on phone. So yeah, research the SHOP applying the rust treatment by looking at all the reviews you can, and don’t take one mechanic’s word for it, or your buddy Joe’s word for it. And you really must check that the product has at least been applied everywhere it needs to go, which is difficult if you can’t watch the techs or if the owner of the shop is…uh…well, I have lots of words that are probably unprintable. Last couple of years I’ve just bought several spray cans of rustproofer, (usually the Formula 3000…it has proven very effective on my trailer hitch left out in the elements all winter), a couple of different types of extension wands to get interior sections, and done the rustproofing myself. If you have an older, mint condition vehicle, and do not want to risk rust, I think this is the only safe way to go.

  3. I have rustproofed or undercoated most of my 30 plus vehicles over my life and highly recommend it. I am however not too thrilled with my Corrosion Free rustproofing that I received this year (my first experience with Corrosion Free). It has been 5 months since the job was done and my car is still dripping from every drain hole along the bottom of my doors, trunk, etc. To me a little dripping or seepage is fine and a good indication of good coverage and a job well done, however this product is sold as “no drip”. So while I can appreciate the thorough job done by the worker I am not all giddy about the product.

  4. I’ve been using Rust Check on my vehicles since 1984 and I’ve never, ever had a rust problem of any kind and some of these vehicles I owned for more than 12 years (southern Ontario). This product does however seem to present problems with rubber components which can stretch and expand over time and I had problems with motor mount bushings and pollution control gaskets on different cars after ~9 years in each case. (I believe this is true of any oil based spray application products.) On balance I would still definitely recommend it.

  5. I have been getting my vehicles treated by Krown for as long as they’ve been around, and I agree it’s more the quality of the application than the product itself. You can develop a product that protects the car like no other, but if it’s applied by an inexperienced or improperly trained technician, or moreover, a technician that is bored, tired, or simply doesn’t give a s**t, your vehicle is not going to be properly protected. I don’t like they way most garages won’t let you watch. They give you some BS about liability and insurance, but in reality, they’re not letting you watch so you don’t see what a lousy job they’re doing. Some shop owners are very diligent about making sure their techs do a proper job, and those are the ones I go back to. I’ve had everything from no plugs installed in the drilled holes, to such a poor job that the inside of 3 out of 4 wheel wells was completely dry after the application. Those are the ones that I don’t patronize again. So again, I feel it doesn’t matter which rustproofing product you try. Properly applied any of them are going to do wonders protecting your investment. Improperly applied, and you’re just throwing your money away, and worse, giving you a false sense that it’s protected when in fact, it’s not.

  6. Ķrown rust proofing is a pure waste of money. Learned from experience. Had a car sprayed so they say.I checked when I got home. They sprayed approximately 2sq.feet behind the gas tank, not a drop anywhere else. The plugs from previous spay were never removed. This is a factual experience.

  7. When I began comparison shopping for a rust-proofing product, for the used, but rust-free vehicle, that I purchased 2 years ago, to protect my investment, I based my final decision to buy the ‘Corrosion Free Complete Rust Cure’ C package, their most expensive option, on the recommendations made on this page. It certainly appeared to be the superior product, as well as the best value for the money. Imagine my surprise now to learn that, because it was applied to a used vehicle, the much vaunted ‘Corrosion Free’ Warranty does not apply! This fact does not appear anywhere in this page’s review of the different rust-proofing products profiled. That’s quite a condition to be blatantly absent! Given my experience, cansumer.ca giving ‘Corrosion Free’ your highest recommendation certainly now ‘rings very hollow’. I am now very hesitant to continue using ‘Corrosion Free’, now that I’ve learned the hard way, that they don’t stand behind their product.

  8. My experience with rust proofing has been very different than expected. I have used both krown and rust check and have had very different results than others. I had one truck I used krown and had both rear fenders rust out completely. I now use rust check on my current truck and have had zero rust anywhere on it it. But my experience is probably more related to how it was applied more than what brand it was. In the old days we just oil spray our cars and even that worked well if done correctly. So my opinion is how well the job is done is far more important than what one you use. And don’t be afraid to go take a look at the job they have done and watch them do it.

  9. Great summary, thanks! I’d like to see an additional section discussing whether it’s starting rust proofing on a used vehicle that already has signs of rust. I recently bought a five year old used car. The major items underneath only have light surface rust, but the exhaust has wider spread rust, and some large flakes around the bolted parts. I’m wondering if rust proofing is a waste in a scenario like this.

  10. Been using Krown for 8 years now. Have never kept a vehicle longer than 3 years so can’t speak to it’s worth after that, but no issues in 3 years!

  11. I have been using Krown for over 4 years on my vehicle when I bought it back in 2016. There is no sign of rust at all despite being daily driven in harsh winters. Definitely recommend.

  12. We have used rust check on past vehicles, and i regularly spray suspension with can of rust check when changing snows etc.
    One of the biggest issues we had is where they drill the hole to access the rocker panels – large (1/2 inch or so) hole drilled in the top surface of our rocker panels was the only place we noticed significant rust on our last minivan. Salt/dirt collected around the edge of the plastic plug and that’s where the corrosion started. Perhaps they have become better now at locating holes away from these areas.

  13. My experience: I have used Krown over the last several years on my sedan. Result: rusted rear fender and rusted rocker panels where there was little to no visible corrosion. My understanding was, even if there was some corrosion, the treatments were supposed to stop it from advancing. I knew of someone else who used Rust Check with a car he bough from Quebec (where they use a lot more salt). 10 years of ownership and no advancement in his corrosion. The condition of my car was about the same as his when he bought it but in about four years I have rust penetrations as if my car was never treated. Now, I have extensive body repairs to do no thanks to Krown. Clearly the Krown treatment is not good in comparison to the Rust Check.