Preventing rust is cheaper than repairing it. Cars rust from the inside out, in the spots you cannot see: in box sections and sills, behind seams, under the car and in the wheel arches, where moisture and road salt collect. Rust prevention and conservation is about protecting those spots, and treating existing rust before it eats through. This guide explains why and where cars rust, in what order you work, and which product suits which job. You will find all products in the rust prevention and conservation category.
Where cars rust
Rust forms where steel, moisture and oxygen meet and do not dry quickly. The risk spots are always the same: enclosed cavities and box sections that hold moisture, seams and overlaps where water creeps in, the exposed underbody that endures stone chips and grit, and the wheel arches behind the plastic liners. The approach differs per spot, which is why there is no single product for everything but a range that each play their own role.
The right sequence, step by step
De-rust. Remove old, loose coatings and as much loose rust as possible by sanding or brushing, then degrease thoroughly.
Convert existing rust. On open, accessible spots where some rust remains, convert it with a rust converter into a stable base.
Prime and coat bare steel. Prime the bare steel and finish it with a durable anti-corrosion coating.
Conserve cavities. Inject a creeping cavity wax into box sections, sills and doors so they are protected from the inside out.
Protect the underbody. Apply an underbody wax to the exposed underside, black where colour does not matter or transparent on visible areas.
Seal the seams. Seal welded joints and overlaps with a flexible seam wax.
Which product for which job
The choice depends on the spot and the goal. For existing rust on an open surface you use the rust converter Bilt Hamber Hydrate-80; it turns the rust into a base you coat over. For an invisible, temporary shield on functional parts such as braking surfaces and suspension you choose the creeping corrosion inhibitor Bilt Hamber Atom-Mac, which you reapply after wet weather. For lasting protection you choose a Dynax wax; the table below shows which.
Dynax | Zone | Colour | Film |
|---|---|---|---|
Cavities, box sections, sills | Brown, translucent | Soft, self-healing, creeps | |
Exposed underbody | Dark brown, black | Firm, abrasion-resistant, no peel | |
Visible areas, over paint | Transparent | Firm, virtually invisible | |
Seams and welded joints | Grey | Fast, flexible, brushable |
The niche jobs
Besides the main products the range covers a few specialist jobs. The self-etching weld-through primer Bilt Hamber Etchweld protects steel and keeps working through the welding process. The two-part anti-corrosion coating Bilt Hamber Epoxy Mastic is the durable finish over bare steel or over a cured rust converter. And for stone-chip protection on the underside you use the oversprayable Motip Anti-Gravel underbody protection.
See it in practice
In this demonstration by Bilt Hamber you see how the Dynax wax holds off corrosion compared to an alternative.
Preventing rust or removing flying rust
This guide is about preventing and treating rust on the structure: underbody, cavities and seams. If you see brown speckles on your paint or wheels, that is usually flying rust, iron particles from brake dust and rail wear that settle on the paint. That is a different job; for that you read the guide removing flying rust and fallout.