Skip to content
mobilerustdoctorAny vehicle underseal — at your home

The honest guide

How to DIY underseal your car, van or motorhome.

No gatekeeping — here's exactly how we do it, so you can too. The kit you need, the eight steps in order, and the two mistakes that quietly ruin most DIY jobs.

Jump to the stepsAsk us a question
A vehicle lifted on ramps being undersealed at home

Should you DIY — or call us?

DIY makes sense if you're confident, properly equipped, and have a safe, level place to lift the vehicle. If any of that gives you pause, this is a job worth handing over — getting it wrong can trap moisture and make rust worse. We bring lab-proven materials, do the cavity injection most people skip, and leave you a before & after video.

See what we'd charge instead

Before you start

The kit you'll need

  • Axle stands and a trolley jack (or ramps) — never work under a car held only by a jack
  • Eye protection, a respirator mask, gloves and old clothes
  • A wire brush, needle scaler or angle grinder with a wire cup for de-scaling
  • Panel wipe / degreaser and clean rags for preparation
  • Bilt Hamber Dynax UB for the underbody, plus a cavity wax and an injection lance for the hollow sections
  • A Schutz / underbody gun (or aerosol versions for smaller jobs)
  • A tarpaulin or dust sheets to protect your driveway

Diagnose → treat → protect

The 8-step method

  1. 01

    Lift and secure the vehicle

    Jack the car up and lower it onto axle stands or drive it onto ramps. Chock the wheels. Your safety is non-negotiable — never go under a vehicle on a jack alone.

  2. 02

    Remove undertrays and clean

    Take off plastic undertrays so you can reach everything. Brush off loose dirt and let the underside dry fully — sealing over damp metal is the number one cause of trapped rust.

  3. 03

    De-scale the rust

    Mechanically remove loose, flaky rust back to sound metal with a wire brush, needle scaler or grinder. You're not chasing bare metal everywhere — just removing what's loose so the coating bonds.

  4. 04

    Degrease and mask

    Wipe down with panel wipe to remove oil and grime. Mask off the exhaust, brakes, driveshafts, sensors and anywhere you don't want coating.

  5. 05

    Inject the cavities first

    This is the step most DIYers skip — and it matters most. Feed a wax lance into the sills, arches and inner chassis and inject cavity wax until it weeps from the drain holes. Rust starts inside; this is where you stop it.

  6. 06

    Coat the underbody

    Apply an even coat of Bilt Hamber Dynax UB across the whole underside. Build it up rather than flooding it — thin, consistent coverage lasts longer than thick runs.

  7. 07

    Check and tidy

    Remove masking, refit the undertrays, and check the brakes and exhaust are clear of coating. Wipe any overspray off your driveway before it cures.

  8. 08

    Re-check each year

    Have a look underneath each autumn before the salt season and touch up any chips. A small top-up beats starting again.

The two mistakes that ruin DIY jobs: sealing over damp or dirty metal, and skipping the cavity injection. Get those two right and you're most of the way there.

Good to know

DIY questions

Is it worth doing it myself?
If you're confident, equipped and have somewhere safe to lift the car, DIY can save money. The two things people get wrong are skipping the cavity injection and sealing over damp or dirty metal — both undo the work. If you'd rather it was done properly with lab-proven materials and a before/after video, that's exactly what we do.
What's the difference between Bilt Hamber Dynax and a lanolin spray?
Bilt Hamber Dynax UB is tested in ASTM-B117 salt-spray chambers, so there's independent proof of how long it resists rust. It's tougher and longer-lasting than lanolin-based products (e.g. Lanoguard), which is why we use it. A cheap lanolin spray over only the visible underside misses the cavities where rust actually begins.
How long will a DIY job take?
A first-timer should set aside a full day for a car — most of the time goes on safe lifting, de-scaling and proper preparation, not the coating itself. Rushing the prep is the fastest way to a poor result.
Can I just spray over existing rust?
No. Loose, flaky rust must be removed back to sound metal first, or it keeps spreading underneath the coating. Surface staining is fine to coat over once de-scaled; structural rot that's gone through the metal needs welding, not wax.

Rather not crawl under the car?

We'll bring the lab-proven materials, do the cavity injection, and send you the before & after video — all on your driveway.

Book onlineWhatsApp 07440 428 007
WhatsAppBook online