Beyond The Bubble's: The MX5 Rust Map
- Chassis Clean
- Jan 7
- 3 min read
BUILT FOR FUN ✅
BUILT FOR SCOTLAND ❌
Sills & Drain Holes: The Salt-Water Bath
The Trap:
Sills are double-skinned box sections that collect road grime, salt, and leaves from the wheel arches.
The Mechanism:
Debris quickly blocks the tiny factory drain holes underneath. The sill becomes a non-draining cavity holding a salty, caustic paste.
The Consequence:
Structural failure here is an immediate MOT fail, especially near safety mounts (DVSA MOT Tester’s Manual).Clean-looking sills can be paper-thin inside.
✅ Your Protection Plan:
You need internal cavity cleaning and the injection of flexible cavity wax to penetrate seams and stop moisture from clinging to the metal inside.
Chassis Rails: Rust from the Inside Out
The Trap:
These main structural box sections are low, exposed, and collect road spray.
The Mechanism:
Moisture and salt get inside through tiny drain holes or damaged underseal and become trapped. The internal surfaces never dry.
The Consequence:
Structural integrity is silently compromised. We have seen rails that look fine externally but crumble when pressure-cleaned. Failure here means the chassis is unsafe and is a non-negotiable MOT failure.
✅ Your Protection Plan:
The standard factory underseal fails here because it is brittle. We apply a flexible, penetrating protection that moves with the car and prevents water from getting trapped underneath.
The Grime Shelf: Dog-Leg/Arch Seam
The Trap:
The complex junction where the sill meets the rear arch and fender is a perfect horizontal shelf.
The Mechanism:
It catches and holds compacted road grime and salt spray. The factory coating here is stressed by welds and is often thinnest.
The Consequence:
This is often the first visible sign of failure. It usually means the internal sill rot is severe and has finally breached the outer panel skin. Do not just patch it.
The Solution:
If the dog-leg is compromised, the sill cavity needs urgent professional inspection.
The visible damage is never the extent of the problem.
The Tell-Tale Sign:
'Frankenstein' Bolt Mounts (NA/NB)
The Trap:
These captive nuts are welded into the rear chassis rails (used for hardtops or roll bars).
The Mechanism:
Because the captive nut is welded into the internal cavity (where salt and moisture are trapped), the metal around it corrodes heavily.
The Consequence:
When an owner tries to use the bolt, the nut will often seize or spin inside the rail. This is not the cause of rust, but it is a widely known, obvious symptom of advanced internal chassis corrosion.
The Solution:
Don't ignore a seizing bolt. It is your chassis giving you a serious warning.
Suspension Mounts: The High-Stress Attack
The Trap:
Suspension components live right in the firing line, catching abrasive salt spray and grit.
The Mechanism:
The constant stress and loads on these mounting points cause any thin, brittle factory underseal to micro-crack.
The Consequence:
This creates a direct path for salt to attack the metal, leading to seized bolts, accelerated bushing wear, and high repair bills.
✅ Your Protection Plan:
We strip, treat, and re-coat these high-stress areas with specific, flexible, self-healing protective coatings that prevent cracking and stop corrosion from creeping back in.
SCOTTISH WINTERS ARE TOUGHER THAN YOUR MX-5's COATING.
We specialise in tackling the exact corrosion mechanisms created by Scotland's climate.
We clean, treat, and protect every inch.
Inside the sills, inside the rails.
STOP THE ROT BEFORE THE NEXT MOT.
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