Techshield Underseal & Cavity Wax Explained: Which One Goes Where
Techshield is Rustbuster’s professional underbody protection range, and it covers every part of the job: a tough underseal for the underside, a cavity wax for inside box sections, a clear heat-resistant wax for engine bays, and a paintable stonechip for lower panels. The names can be confusing, and using the wrong one in the wrong place causes problems later. This guide explains what each one is and exactly where it goes.
The Techshield range at a glance
| Product | What it is | Where it goes | Paint over it? | Format |
|---|---|---|---|---|
| Underbody Schutz | Tough black bitumen underseal | Floorpan, chassis, wheel arches, sills, spoilers | No: bitumen only | 1L can (brush or Schutz gun), 500ml aerosol |
| Cavity Wax | Penetrating, clear-white wax | Inside sills, doors and box sections | Not needed: goes inside | 500ml aerosol with adapter |
| Heat Resistant Clear | Clear, dry, non-tacky wax, heat resistant to 200°C | Engine bays, gearboxes, suspension, visible underbodies | Stays clear | 1L, 2.5L, 5L tin; 400ml aerosol |
| Stonechip | Textured resin and rubber coating | Sills, valances, lower panels you’ll paint | Yes, all paint systems | 1L tin: black, grey, white |
Techshield Underbody Schutz: the tough black underseal
Techshield Underbody Schutz is a professional-grade, bitumen-based underseal. It forms a tough, closed, elastic coating that resists salt, moisture, acids and alkalis, stands up to stones and gravel, and deadens road noise. It has been tested to 1000 hours in a salt-spray cabinet, which Rustbuster rate as equivalent to around five years of typical UK road conditions, with an annual inspection recommended. It bonds well to pre-treated metal and factory finishes, and it’s compatible with original PVC underseal.
- 1 litre can: apply by brush or with an undercoating Schutz gun, which screws straight onto the can. At a 700µm wet layer and 20°C it’s dust-dry in 3–5 hours, touch-dry in 12–16 hours and dry through in a day.
- 500ml aerosol: handy for arches, spoilers and touch-ups; dust-dry in about an hour.
Techshield Cavity Wax: protection from the inside
Sills, door bottoms and box sections rust from the inside out, where you can’t see it. Techshield Cavity Wax is a penetrating wax that creeps into these hidden areas and leaves a weather-resistant, protective film with excellent adhesion. It also resists weak acids and alkalis.
Warm it up
The aerosol should be at room temperature; it works best between 15 and 25°C.
Shake for two minutes
Shake the can thoroughly before use.
Apply generously inside the cavity
Feed the adapter into existing holes and grommets and coat the inside of the cavity generously, working along its full length. Keep drain holes clear.
Clean the valve
After use, turn the can upside down and press the nozzle for about five seconds so it doesn’t block.
Techshield Heat Resistant Clear: invisible protection
Where you don’t want black, Techshield Heat Resistant Clear forms a hard, transparent, dry and non-tacky film that won’t attract dirt. It resists heat up to 200°C, so it’s ideal for engine bays, gearboxes, axles and suspension, and for underbodies on show and restored cars where you want to see the metal. It’s safe on rubber, plastics and mixed metals, and one litre covers around 12m². It comes in 1, 2.5 and 5 litre tins or a 400ml aerosol. Read more in our clear rust protection guide.
Techshield Stonechip: the paintable option
For sills, valances and lower panels that will be painted in body colour, Techshield Stonechip gives a tough, textured, stone-chip-resistant finish that can be over-painted with all paint systems. See our full stonechip and seam sealing guide.
Techshield or Corrolan?
Rustbuster’s other underbody range, Corrolan, is a lanolin (sheep’s wool) wax that stays soft, creeps into seams and self-heals when it’s scuffed. Its honey colour lets you keep an eye on the metal underneath. Techshield Underbody Schutz is the opposite approach: a hard, black, abrasion-resistant underseal. Many owners use both: Corrolan inside cavities and on seams, and Schutz on the most exposed areas. Read our lanolin rust proofing guide and Waxoyl alternatives guide to compare.
The right order for a full underbody job
- 1. Clean, degrease and wash off road salt with Chlor-X
- 2. Treat rust with FE-123, or take it back to bare metal
- 3. Prime bare steel with Zinc Rich Epoxy-Anode or Epoxy Mastic
- 4. Seal seams with Dinitrol 410
- 5. Wax the inside of every cavity with Techshield Cavity Wax
- 6. Coat the underside and arches with Underbody Schutz, or Stonechip where you’ll paint
- 7. Protect the engine bay and visible parts with Heat Resistant Clear
- 8. Inspect every year and touch up
Mistakes to avoid
- Painting over Underbody Schutz. It’s bitumen: only bitumen products go on top. Use Stonechip where you want paint.
- Applying Schutz over rust, dirt or damp. De-rust, abrade and clean first, or you seal the problem in.
- Using underseal inside cavities. Box sections need a penetrating cavity wax that creeps into the seams.
- Blocking drain holes. Wax the cavity but keep the drains open.
- Skipping the annual check. Stone damage happens; a yearly look and touch-up keeps the protection intact.
Looking for Techshield aerosol paints, such as primer, zinc-rich weldable primer, gloss, satin and matt black, and clear lacquer? See our guide to spray painting metal with Techshield aerosols or the full Techshield aerosols range.
Techshield FAQs
What is underbody Schutz?
Schutz is a tough, elastic underseal sprayed or brushed onto the underside of a vehicle to protect it from rust, stones and gravel. Techshield Underbody Schutz is bitumen-based and tested to 1000 hours in a salt-spray cabinet, around five years of typical UK road conditions.
Can you paint over underbody Schutz?
No. Techshield Underbody Schutz is bitumen-based and can only be over-coated with bitumen products. For panels you want to paint, use Techshield Stonechip, which can be over-painted with all paint systems.
Is underbody Schutz the same as underbody wax?
No. Schutz is a hard-wearing bitumen underseal. Waxes such as Techshield Cavity Wax or Corrolan lanolin wax stay softer, creep into seams and are better for cavities. Many owners use wax inside cavities and Schutz on the exposed underside.
How long does Techshield Underbody Schutz take to dry?
From the 1 litre can at a 700µm wet layer and 20°C: dust-dry in 3–5 hours, touch-dry in 12–16 hours and dry through in a day. The aerosol is dust-dry in about an hour.
Which Techshield product goes inside sills and box sections?
Techshield Cavity Wax. It’s a penetrating wax designed to creep into hidden cavities, applied from the aerosol with its adapter. Underbody Schutz is for the outside of the underbody, not inside cavities.
More rust guides: rust-proof your car before winter, 10 steps to complete rust protection and surface preparation.
