Cavity Wax Injection
Rust starts in the places you cannot see. Cavity wax injection feeds a creeping, water-displacing wax into sills, chassis rails and box sections – protecting the closed areas where corrosion begins but cleaning and surface coatings can never reach.
Cavity wax injection protects the inside of a car's closed sections – sills, chassis rails, box sections, doors and pillars – with a creeping wax fed in through existing access points. It is the counterpart to a clean, protected underside: surface coatings guard the metal you can see, cavity wax guards the metal you cannot. It is included in our Full Preservation and Signature programmes and is one of the most effective things you can do for a car you intend to keep.
Where rust actually begins
Most owners watch the outer panels and the visible underside, but corrosion rarely starts there. It starts inside the box sections and sills – the enclosed cavities that trap road spray, condensation and salt and then stay damp long after everything you can see has dried. By the time rust shows on the outside, it has usually been working from the inside for a long time.
That is the problem cavity wax is built to solve. You can dry ice clean and protect every surface you can reach and still lose a sound car from within if the cavities are ignored. Treating them is what separates a cosmetic underside clean from genuine, structural preservation.
How cavity wax injection works
Access. The wax is introduced through existing drain holes and access points using a long flexible lance, so major dismantling is rarely required.
Creep and displace. The wax flows along the seams and folds under its own capillary action, displacing moisture and coating the bare internal metal.
Protect. It cures to a self-healing, water-repellent film that stays flexible and keeps protecting the cavity through the seasons.
Part of a complete underside
Cavity wax works best as part of a properly prepared preservation programme. Before the cavities are injected, the underside is assessed, cleaned and treated where needed, with any failed underseal, trapped contamination or active corrosion dealt with as part of the wider process.
Once the surface protection has been applied, cavity wax is injected into the closed sections – helping protect sills, chassis rails, seams and internal areas from the inside out. For chassis-heavy vehicles such as 4x4s, it is an especially important stage because moisture and salt often sit where you cannot easily see them.
Common questions
What is cavity wax injection?
Cavity wax injection feeds a creeping, water-displacing wax into the closed sections of a car – sills, chassis rails, box sections, doors and pillars. The wax is introduced through existing drain holes and access points with a long lance, then creeps along the seams and folds, displacing moisture and leaving a protective film on metal that cleaning and ordinary coatings can never reach.
Why do the cavities matter so much?
Because that is where rust usually starts. Box sections and sills trap damp and salt and stay wet long after the visible underside has dried. You can clean and coat every surface you can see and still lose a car from the inside out if the cavities are left unprotected. Treating them is what turns a good underside clean into genuine long-term preservation.
Can you inject cavity wax without removing panels?
In most cases, yes. The wax is designed to be introduced through existing access points and to creep along the cavity under its own capillary action, so major dismantling is rarely needed. Where access is genuinely blocked we will tell you, and agree the best approach before going further.
Does cavity wax need topping up?
Over time and through wet winters, yes – which is why it forms part of our annual maintenance. A brief annual inspection lets us check the cavities and top up the wax in high-wear areas so the protection keeps doing its job.
Protect the cavities where rust begins
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