About 5 million tonnes of road salts are used in Canada each year to prevent snow and ice from accumulating on roads and make driving safer. Ontario, Quebec and the Atlantic provinces are particularly heavy users.
However, safer winter driving comes at a cost.
It can cause corrosion damage to vehicles – especially brake linings, frames, and bumpers – as well as roads, bridges, and underground utilities.
There are also environmental concerns – road salts, including sodium chloride (NaCl), calcium chloride (CaCl2), potassium chloride (KCl) and magnesium chloride (MgCl2) are monitored substances on Environment and Climate Change Canada’s Priority Substances List (PSL).
There are less toxic and less corrosive alternatives such as beet and cheese brine, but salt is the cheapest and least-smelly option, so continues to be widely used.
What causes a car to rust?
Rust is the corrosion of iron (steel contains iron) as it reacts with moisture and oxygen in a process called oxidation, which weakens and breaks down the iron into a flaky powder, causing holes to develop.
The electrochemical reaction is accelerated by higher temperatures and the presence of salt, so the spring months when the humidity is higher and the weather is warmer, are the perfect environment for rusting – particularly if there is grime and salt residue left on the underside of your car.
As per my Hyundai Elantra’s owners manual:
Corrosive materials used for ice and snow removal and dust control may collect on the underbody. If these materials are not removed, accelerated rusting can occur on underbody parts such as the fuel lines, frame, floor pan and exhaust system, even though they have been treated with rust protection.
Hyundai Elantra: Exterior Care
Now, the exteriors of modern cars have multiple coating layers that protect the bare metal and prevent it from rusting – as long as they are kept intact:
Modern cars’ metal frames (chassis) are first dipped into a large bath (see video) to be completely and consistently coated with zinc phosphate primer through a process called electrodeposition (also called electro-coat or e-coat primer). This coating acts as barrier that provides complete coverage and consistent thickness, preventing oxygen and moisture from getting to the metal body.
The colored basecoat and acrylic polyurethane “enamel” clear coat (paint without the pigment to give it colour) are then applied, followed by a wax coat to act as a sacrificial layer prevent grime and stains from sticking to the clear coat.
Manufacturers also add plenty of drainage holes along the doors and rocker panels to let the inside of the panels dry out.
If the barrier is rubbed, chipped, dented or cracked off by wear-and-tear or accidents and exposes the bare metal, the car will start to rust. In addition to road salt, dust control chemicals (calcium chloride), acid rain, road tar, insects, ocean air and industrial pollution can also accelerate corrosion.
Rust typically starts:
- Along the bottom of seams and joints on the inside of vehicle’s body panels. Salty water can trickle in past rubber seals, accumulate if the drainage holes become blocked by debris and start rusting from the inside out. The panel seam rust coming from the inside is the big problem, not rust from surface chips. No amount of washing will prevent this.
- Underneath the car where rocks and debris damages the protective coating and moisture-soaked dirt and salt deposits build up. Mud is particularly corrosive because it is slow to dry and holds moisture in contact with the vehicle. This also applies to visible surfaces, but especially to the underside of the vehicle.
- Surface where scratches, dings and nicks caused by rocks, or scrapes and dents cased by accidents that break the protective coatings and paint – particularly on the hood and doors. These are easier to spot, and if found early, to treat and fix.
Here are some examples of how rust has affected vehicles in the past:
- 1995 to 2000 model year Toyota Tacoma trucks were bought back in the US due to rusted out frames that were not coated correctly
- In 2015, 3,000 BMWs were recalled after being exposed to water and salt in Halifax
- 2008 or earlier model years – In 2015, the US National Highway Traffic Safety Administration found that road salt was causing thousands of vehicle brake failures after a 4 year investigation.
What is rust proofing?
Rust proofing is the prevention or delay of the rusting of iron or steel, achieved for cars through the application of an anti-corrosion protective coating on the surface of the metal.
What are the benefits of rust proofing?
Keeping your vehicle rust-free will lead to a:
- Longer lifespan
- Lower repair expenses
- Higher resale/trade-in value
- Lower environmental impact
Should I rust proof my car?
Whether or not you should rust proof your car depends on where you live, how long you intend to keep the vehicle and how much other preventative maintenance you do:
It’s probably worth it if you plan to:
- Keep the vehicle for a period beyond the manufacturer’s rust warranty, and especially if you plan to drive it into the ground
- Rarely, if ever wash your car during the winter or wax it semi-regularly
- Drive often in the winter months
- Drive in an area that uses a lot of road salt in the winter
- The cost of rust proofing is low compared to the value of the car (car is new, luxury, collectible or sentimental)
- Ignore small chips and scrapes
It’s probably NOT worth it if you plan to:
- Return/trade-in the car at the end of its lease
- Sell it before the new vehicle corrosion warranty runs out
- Wash your vehicle after every snowstorm
- Drive infrequently, and less in the winter months
- Drive in an area that primarily uses sand in the winter
- The cost of rust proofing is high compared to the value of the car (car is new, luxury, collectible or sentimental)
- Fix all chips and scrapes immediately
How much salt does your area use in the winter?
Check your area’s winter road clearing or salt management plan to find out how much salt they use. It depends on:
- Road salt is used more in urban areas than rural areas. Salt is not appropriate for use on the gravel roads as it will create potholes, so sand is used instead.
- Cities near bodies of water with milder winters and greater precipitation like Montreal (about 200,000 tonnes), Ottawa (185,000 tonnes), Toronto and Halifax use the most salt.
- Road salt starts to lose effectiveness at -10C and is ineffective below -20C. In the prairies where winters are colder, it’s often too cold for salt to work. Regina, SK typically uses a mixture of 94% sand and 6% salt and Calgary will use a sanding chip mixture of 97% fine gravel and 3% salt when road surfaces are below -10C.
How long do you plan to keep the vehicle?
Will the cost of applying it every year (~$150) over the course of the time you keep the car be offset
Car manufacturers typically offer 5 year, unlimited km corrosion warranties on new cars that cover rust holes in the metal body panels from the lower window line down under normal use and maintenance, including Hyundai, Toyota, Ford and Honda. Volkswagen offers 7 year/unlimited km.
For surface corrosion (no hole), the coverage is slightly shorter: Honda covers for 3 years/unlimited, Hyundai and Ford 3 years/60,000 km.
However, most modern vehicles do not show visible signs of rusting until they are over 5 or 6 years old according to the APA – just as the warranties are expiring. The average life expectancy of a vehicle in Canada is 12.88 years and used cars are retaining more of their value and prices are hitting record highs, so maintaining the vehicle you own is becoming even cheaper than buying another car that it already was.
I would think that between when the new car warranty ends and the average life expectancy of the vehicle is when rust proofing is most worth it – the car is still relatively new and valuable and it will stop rust from spreading any further.
How much maintenance will you do?
Washing off salt and grime – Unless you’re planning to wash your car after every snowstorm, there’s a good chance that you’ll have to drive on some really messy roads, then leave your vehicle to sit in temperatures above freezing the next day. Or worse, park it in a heated garage while it’s still wet.
Repairing minor rust damage – Most rust starts as minor cosmetic damage on its surface and along the bottom of vehicle’s body panels which only affects the appearance of the vehicle. Small holes are generally cheap and easy to repair if dealt with early by filling them with epoxy putty, sanding it, and painting it with a layer of primer, base coat (colour) and clear coat. However, if left to fester, particularly in the vehicle’s frame, it can turn into a safety concern.
Personally, I’d rather spend $150 every year than pay $15 for a car wash every week or two during the winter or try to squeeze under my car to hose it off myself. If you’re able to hoist your car up in the air and pressure wash your entire undercarriage after every winter storm, then all the power to you!
Can you rust proof an aluminum vehicle?
Yes, a vehicle with an aluminum frame or body can be rust proofed, but the value of doing so is somewhat reduced since aluminum corrosion is typically only surface-level and is more cosmetic, than structural in nature when compared to iron rusting. This thin layer of white oxide film forms on the surface and protects the material underneath from further corrosion.
That said, most vehicles that have an aluminum body still have a steel frame, suspension, and other components eg. 2021 Ford F-150) that can be protected with rust proofing. Aluminum is considerably more expensive than steel, so typically only higher-end vehicles such as Tesla Model S, X and Audi A8 are primarily made of aluminum.
When combined with water, the chlorides in common salt (sodium chloride) and acids contained in dirt can penetrate the aluminum oxide film and cause pitting on the surface, producing a white powdery corrosion.
Can you rust proof a hybrid or electric vehicle?
Yes, hybrid and electric vehicles can be safely rust proofed by a qualified technician. Vehicles all have differences that must be taken into account – particularly to ensure the drilling doesn’t hit any wires – and the biggest service providers will have details about how and where to treat them.
Manufacturers do not recommend it and many specifically state it shouldn’t be applied, claiming that coating the electronics, battery, electric motor, and high-voltage electrical wiring will cause damage.
However, many hybrids and EVs include plenty of steel, which of course can rust. The Hyundai Ioniq uses high-strength steel for the structure and aluminum for non-structural panels.
Krown’s formula, for example, has a high dielectric strength, meaning it does not conduct electricity and will not short the electrical systems.
Does rust proofing or drilling holes void manufacturers’ warranties?
No, a professionally applied rust protection such as Rust Check, Krown or Corrosion Free will not void the manufacturer’s corrosion/perforation warranty, including the drilling of holes. However, they may have a case not to cover you if the damage was done due to improper application or drilling.
Car dealers may say that it’ll void your warranty as a scare tactic to get you to buy expensive and ineffective tar undercoating and electronic rust inhibitor modules from them as well as other pricey add-ons, including VIN etching, fabric protection, and extended warranties.
In Canada, modifying your car or installing aftermarket components will not void your car’s warranty, unless the modification causes damage to or breaks other parts in which case your claim can be denied.
What about the holes drilled?
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:
This is where salty water can trickle in past rubber window seals and accumulate 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:
In an ideal world, all of the panels on the car would be removed to get access to the interiors portions of the vehicle instead of drilling holes. However, the time it takes to do this would increase the cost of the service by hundreds of dollars. Drilling holes is faster and cheaper.
If you’re still concerned, you always have the option to opt out of having holes drilled, but protection won’t be as complete.
Is rust covered by car insurance?
No, car insurance policies do not typically cover damage to your vehicle caused by the normal wear and tear of operating it, including rust and corrosion.
Can you rust proof a used car that already has rust?
Yes, you can rust proof a vehicle if it has already started rusting. It will seep into the rust and push out moisture, slowing down its progress.
- Krown states it is absorbed into existing corrosion and pushes out any moisture, thus slowing any further corrosion down significantly.
- Rust Check states that while it will not repair damage already done to older vehicles but it will inhibit the progression of rust in problem areas.
When should I rust proof my car?
The best time of year to rust proof is in the spring. This is when the humidity is higher and the weather is warmer, creating the perfect environment for rust, particularly if there is grime and salt residue left on the underside of your car.
If your vehicle has never been protected, then the best time to spray it is right now. If you want the service provider’s warranty coverage, your car must be rust free, recently purchased and less than a few model years old.
How often do I need to rust proof my vehicle?
Rust proofing companies recommend getting the service done annually, and it must be done that frequently in order to maintain their warranties.
The spray slowly dissipates over time and eventually the metal will once again be exposed to the elements. It will wear away faster in high spray areas such as wheel wells and the bottom of rocker panels.
However, a vehicle in a benign environment (eg. Trenton, ON) needs application far less frequently than one exposed to a severe environment (eg. Montreal, QC) according to a 2006 study conducted by the Department of Defense Research and Development to review corrosion control and prevention on army vehicles.
Depending on your driving habits, what kind of roads you drive on, and the climate, you can determine if you should do it every year, or every 2. Every 2 years is much better than not doing it at all.
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:
- Krown T-40/KL73 on Amazon
- Rust Check Coat & Protect at Canadian Tire
- Fluid Film at Canadian Tire
- Corrosion Free 3000 on Canadian Tire or Amazon
You can also get a spray gun from Canadian manufacturer Lemmer on Amazon and follow Canadian YouTuber 4DIYers’ excellent video to apply any of the following yourself:
- Krown T-40/KL73 on Home Hardware
- Rust Check Coat & Protect at Canadian Tire
- Fluid Film at Canadian Tire, (1 gallon) or Amazon
- Rust Cure/Corrosion Free 3000 on Amazon
However, a professional service will likely be quicker and more precise, and prevent any from getting where it shouldn’t, such as on the brakes, exhaust and drive belts.
How to prevent my car from rusting?
The best ways to prevent your car from rusting are to:
- Remove stains – insects, road tar, tree sap, bird droppings, industrial pollution and similar deposits can damage your vehicle’s finish if not removed immediately. Bird droppings are especially corrosive and may damage painted surfaces in just a few hours.
- Repair scratches and chips – Touch up deep scratches and stone chips as soon as you notice them to reduce the spread of corrosion. Minor issues are cheap and easy to fix if repaired promptly, while exposed metal will rust can develop into a major repair expense. You can do this yourself, or if it’s a big job, contact a reputable professional to help you. See touch up paint pens at Canadian Tire and Amazon
- Wash your car regularly, including underneath – In the winter, aim to wash the underside of your car at least once a month. Doing this will help extend the life of the protective coating which protects your car from rust. In more severe environments, wash as often as once every 2 weeks. Clean the underside thoroughly when winter is over.
Use a pressure washer to ensure that mud and road grime is actually removed and not just wetted, which would accelerate corrosion. Be thorough and pay special attention to the components under the fenders and those that are hidden from view. - Wax your car – Protects the clear coat layer from surface scratches, UV exposure, bird droppings, hard water and acid rain.
- Keep your garage dry – Don’t park your car in a damp, warm, poorly ventilated garage as that accelerates corrosion. If the vehicle is still wet from washing or covered with snow, ice or mud, leave it outside to dry first or leave the garage door open for a while to let everything dry out.
- Inspect and clear drainage holes – Make sure the drain holes in the lower edges of the doors and rocker panels (below the doors) are kept open and clean so that moisture can escape and water can’t collect.
Over to you
We’re interested to know – do you think rust proofing is worth it? If so, where in Canada do you live? Let us know by leaving a comment below!
