Road Salt Can Fail Your MOT — Here’s What It Does Underneath Your Car

9 gen 2026

Salt-driven corrosion can strike anywhere… and it gets expensive fast

That right there is road salt — and it’s one of the biggest reasons vehicles rust faster in winter.

You might not notice it at first, because most of the damage happens out of sight… underneath.

But once corrosion takes hold, it can go from “a bit of surface rust” to serious structural issues — and in some cases, an MOT failure.

Let’s look at what salt really does to the bottom of a car, and why it’s worth protecting early.

The real effects of salt: an MOT failure

Here’s a perfect example of what winter salt can lead to.

We can see an MOT failure, caused by corrosion that’s become so severe the tester had no choice but to fail it.

That’s the thing about rust:

It can hit:

And once it starts weakening metal, it stops being cosmetic and becomes a safety issue.

Rust leads to structural weakness when left untreated.

And if it gets worse, it can turn into:

In this case, the vehicle has failed its MOT — and now it needs welding.

That means time off the road, labour costs, and the kind of bill you never wanted in the first place.

Winter roads are often covered in a mix of:

Every drive sprays that mixture into hidden seams and underbody areas, where it can sit and do its damage repeatedly — day after day.

That’s why winter corrosion can ramp up so quickly.

If road salt and grit are what drive corrosion, then the best approach is stopping it early — before you’re facing an MOT fail and a welding job.

✅ Covers the underbody and hard-to-reach areas
✅ Helps protect metal from winter salt exposure
✅ Ideal before (and during) gritter season

Salt damage is preventable. But once corrosion becomes structural, it gets expensive fast.

Protect it now. Save money later.