Every spring we get the same conversation. Someone brings in a five-year-old car, points at a bubble of rust on the rear wheel arch and asks how it happened, because the car has never been in an accident and always looked clean.
It happened between December and April, underneath, where nobody was looking.
Why salt is worse than dirt
Dirt sits on your car. Salt works on it. Road salt lowers the freezing point of water, which is exactly why the city spreads it, and the resulting brine is far more conductive than plain water. Corrosion is an electrochemical process, so brine does not just sit on bare metal, it speeds up the reaction.
Two things follow from that. Salt keeps working as long as it is on the car, and it does the most damage in the places you never wash: the underbody, inside the wheel arches, the seams under the doors, the pinch welds along the sills.
The part people miss: a car can look spotless from three feet away and be actively rusting underneath. The paint you can see is the part best protected. The metal you cannot see is the part taking the hit.
When it is worst
The dangerous days are not the coldest ones. Corrosion needs liquid water, so the damage accelerates when salt gets wet and stays wet:
- Right after a thaw. Salt that has been sitting dry as powder turns back into brine the moment the temperature climbs past freezing. A mild week in February does more harm than a deep freeze.
- Slush season. Wet salt packs into the arches and under the car and stays there for days.
- Parking in a heated garage. This one surprises people. Driving a salted, wet car into a warm garage keeps the brine liquid and warm all night, which is close to ideal conditions for rust. A car parked outside in a hard freeze is, briefly, safer.
How often to actually wash
Our honest guidance for a Toronto winter, not the version designed to sell you the most washes:
- Every two weeks through the salt season is the sensible baseline for a car that lives outside and is driven daily.
- After every thaw matters more than any fixed schedule. If the temperature jumps above freezing and the roads go wet and white, that is the wash that counts.
- Do not bother washing at minus 20 with more salt going down tomorrow. Wait for the thaw and spend the money once.
- Always get the underbody done, not just the paint. A wash that only cleans what you can see is missing the part that rusts.
That last point is the whole argument. An underwash is $30 to $50 depending on size. Rust repair on a wheel arch is a body shop job costing several hundred dollars and it never quite looks original again.
What helps, in order
- Rinsing the underbody. Unglamorous, cheap, and the single most effective thing you can do.
- Salt removal on the interior. The white tide lines on your carpets and door sills are salt that came in on your boots. Left alone it works into the fibres and stains permanently. We price this by section, $40 each, with 25% off if you do all four.
- A coating before winter, not after. Protection is preventative. Applying it in April protects the car from the season that just finished.
- Washing after the thaw, not on a schedule. Timing beats frequency.
The honest limits
No wash and no coating makes a car immune. A ceramic coating protects painted surfaces and makes them far easier to clean, but it is not underbody rustproofing, and anyone who tells you their coating stops rust underneath is selling something. Salt gets into seams no product reaches. The realistic goal is to keep the exposure short, not zero.
Nothing here is complicated. It is just the stuff that is easy to skip in February, and expensive to discover in year five.
Getting the salt off before it settles in
Exterior wash from $20, underwash from $30, salt removal $40 a section with 25% off all four. Book online and 10% comes off automatically.
Book a winter wash →