KBS Cavity Coater is a single-step, super-penetrating corrosion inhibiting coating (CIC) that protects the inside of enclosed metal cavities where primers and topcoats cannot reach. Cavity Coater wicks into welds and seams by capillary action, displaces water on contact, and cures to a self-healing film rated for more than 4,000 hours of ASTM B-117 salt spray exposure on steel.
Cavity Coater is applied with the KBS Cavity Wand through a 1/4-inch access hole to treat rocker panels, boxed frames, inside doors and fenders, deck lids, tailgates, and floor seams.
4,000+ hrs
ASTM B-117 Salt Spray
−60°F
No Cracking or Flaking
125 sq. ft.
Aerosol Coverage at 1 Mil
1/4 in.
Access Hole Required
Enclosed cavities are where vehicles actually rot from. Water and road salt collect inside rocker panels and boxed frame rails, and the exterior paint that protects the outside of the panel never reaches the inside face. Cavity Coater is the product that treats that side of the metal.
Cavity Coater does not require bare metal. It goes over bare, painted, or lightly rusted surfaces after loose scale is knocked off, which is what makes it practical on an assembled vehicle you are not tearing down.
Over 4,000 hours of ASTM salt spray protection. Made in USA. Satisfaction guaranteed.
Cavity Coater Video Overview
Cavity Coater differs from ordinary rust preventives in three measurable ways: it penetrates weld seams by capillary action instead of sitting on the surface, it displaces water on contact rather than trapping it underneath, and the cured film self-heals after minor abrasion. Salt spray resistance exceeds 4,000 hours on steel under ASTM B-117.
- 4,000+ Hour Salt Spray Protection: Exceeds ASTM B-117 testing on steel, delivering over four times the protection of conventional cavity waxes.
- Super-Penetrating: Wicks into welds and seams through capillary action, reaching surfaces where primers and topcoats cannot penetrate.
- Self-Healing Film: The protective film closes back over itself after minor abrasion, maintaining corrosion resistance without reapplication.
- Water Displacing: Displaces water on all metal surfaces on contact, stopping corrosion before it can establish.
- No Cracking to −60°F: Will not crack, flake, or fail even in the most extreme cold climates.
- Chemical Resistant: Resists alkaline solutions, most chemical and acid vapors, road salt, steam, and salt water.
- Lubricating Properties: Reduces friction and protects against carbon fusion, making disassembly easier when repairs are needed later.
- Multi-Surface Compatible: Works on steel, aluminum, cadmium, magnesium, and all common metals with no pitting.
- Minimizes Replacement Costs: Long-lasting protection reduces parts wear, corrosion-related repairs, and maintenance frequency over time.
Cavity Coater is used inside any enclosed metal cavity: rocker panels, boxed frames, inner door and fender panels, windshield cowls, trunk lids, hoods, A-posts, B-posts, tailgates, and the back sides of bumpers. Cavity Coater also serves as an anti-seize on nuts, bolts, shafts, pipe fittings, and chain drives.
- Automotive Enclosed Cavities
- Boxed frames, rocker panels, inside doors, inside car and trailer frame rails, windshield cowls, trunk lids, hoods, inside A-posts, inside B-posts, inside front and rear fenders, inside tailgates, and back sides of bumpers. Use Cavity Coater anywhere a typical cavity wax would be used.
- Weld Seams
- Cavity Coater wicks into weld seams by capillary action, so corrosion protection starts at the weld itself rather than at the surface around it. Cavity Coater also insulates between unlike metals to slow galvanic corrosion.
- Anti-Seize and Anti-Corrosion
- Nuts, bolts, and screws; shafts; pipe fittings; gaskets; press-fit assemblies; valve assemblies; taps and drills; pump mountings; packing glands; chain drives; metal fittings; and general machinery.
- Marine and Industrial
- Any enclosed metal cavity exposed to moisture, salt air, road spray, or chemical vapor. Cavity Coater is used on trailers, marine framing, fleet vehicles, and equipment where long-term internal protection is required.
Does Cavity Coater Work on Aluminum and Other Non-Ferrous Metals?
Cavity Coater passes compatibility testing on cadmium, magnesium, and aluminum with no pitting, so it is safe on mixed-metal assemblies. That matters most at points where steel fasteners meet aluminum panels, because Cavity Coater's film insulates the two metals from each other and slows the galvanic corrosion that normally starts at those joints.
The KBS Cavity Wand is a 36-inch flexible applicator that snaps onto a Cavity Coater Aerosol can and sprays 360 degrees at the tip. The Cavity Wand fits through a standard 1/4-inch access hole, so rocker panels and boxed frames can be coated without drilling new or larger holes in body panels.
- 360-Degree Spray Tip: The tip sprays in all directions at once, so a single pass coats the full inside of the cavity with no repositioning.
- Attaches Directly to the Aerosol: The Cavity Wand pushes onto the Cavity Coater Aerosol spray tip with a slight twist. No tools or adapters required.
- Reaches Enclosed Areas: The flexible 36-inch wand feeds into rocker panels, boxed frames, door interiors, and other cavities that cannot be reached any other way.
- Requires Only a 1/4-inch Access Hole: Sized to pass through a standard 1/4-inch hole, which is usually an existing drain or assembly hole on the panel.
- Very Easy to Clean: Invert the can and spray for 10 seconds after use to flush the wand completely. Ready for storage or reuse.
One Cavity Coater aerosol covers 125 square feet at 1 mil dry film thickness, a quart covers 200 square feet, and a gallon covers 800 square feet. A typical car or light truck needs one to two aerosols to treat all rocker panels, doors, and frame rails. Actual coverage varies with surface porosity and wand speed.
| Size | Coverage at 1 Mil | Best For |
|---|
| Aerosol | 125 sq. ft. | Single vehicles, spot treatment |
| Quart (32 oz.) | 200 sq. ft. | Full vehicle, small shop |
| Gallon (128 oz.) | 800 sq. ft. | Multiple vehicles, shop use |
| 5-Gallon Pail | 4,000 sq. ft. | Fleet and commercial |
| 55-Gallon Drum | 44,000 sq. ft. | Large fleet, industrial |
Pro Tip: Quart and gallon sizes are thinned 30 to 50 percent with KBS #1 Thinner or mineral spirits and sprayed through a KBS Schutz Underseal Spray Gun with a 48-inch 360-degree wand at 90 to 150 PSI. Stir 3 to 5 minutes before and after thinning.
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Shop KBS #1 Thinner →
Cavity Coater differs from standard cavity wax in that Cavity Coater penetrates rather than coats: it wicks into weld seams by capillary action and displaces water at the metal surface, where wax bridges over the seam and can trap moisture beneath it. Cavity Coater is rated above 4,000 hours of ASTM B-117 salt spray, roughly four times a conventional wax.
| | KBS Cavity Coater | Standard Cavity Wax |
|---|
| Salt spray resistance | Over 4,000 hours, ASTM B-117 on steel | Varies, commonly under 1,000 hours |
| Behavior at a weld seam | Wicks into the seam by capillary action | Bridges over the seam surface |
| Water already on the metal | Displaced on contact | Typically sealed in beneath the film |
| Cold-weather behavior | No cracking or flaking to −60°F | Varies, many waxes crack or shed in hard cold |
| Minor abrasion | Film self-heals | Leaves an open path to bare metal |
| Anti-seize on fasteners | Yes, lubricating and resists carbon fusion | Generally not intended for this use |
Standard cavity wax is still the easier choice when a thick, visible, high-build barrier is wanted on an exposed underbody surface rather than inside a sealed cavity, and heavy-bodied wax is more forgiving of a wet or oily surface than Cavity Coater, which needs the metal to be dry. For anything enclosed, penetration matters more than film build, and that is where Cavity Coater wins.
Cavity Coater is sprayed in one thin, even coat at roughly 1 mil. Hold the aerosol 8 to 12 inches from the surface, cover completely without over-saturating, then wait 10 minutes for the coating to wick into seams and weld joints. Wipe away any excess with a clean rag lightly dampened in mineral spirits.
The Cavity Wand feeds through an existing 1/4-inch access hole in the frame rail. Withdraw at about one foot per second while the tip sprays 360 degrees.
Aerosol With the Cavity Wand
- Shake the can extremely well before use, and again periodically while spraying.
- Push the Cavity Wand onto the spray tip with a slight twist. Work between 70 and 80°F for best flow.
- Insert the wand into the cavity through a 1/4-inch access hole.
- Depress the tip and withdraw the wand at about one foot per second. Repeat as needed for complete coverage.
- Invert the can and spray for 10 seconds to flush the wand before storage.
Bulk Quart and Gallon Through a Schutz Gun
- Bring Cavity Coater to room temperature and stir 3 to 5 minutes until uniform.
- Thin 30 to 50 percent with KBS #1 Thinner or mineral spirits, then stir another 3 to 5 minutes.
- Spray through a KBS Schutz Underseal Spray Gun with a 48-inch 360-degree wand at 90 to 150 PSI.
- Move the wand about one foot per second, varying air pressure and speed to hit 1 mil dry film.
- Wipe off excess with a rag lightly dampened in mineral spirits.
Safety note: When Cavity Coater is sprayed into a sealed area such as a door panel, solvent vapor can take several hours to escape. Keep the area away from heat, sparks, electrical devices, and open flame during that time, and always work with adequate ventilation while wearing gloves and safety glasses.
Do You Have to Remove Rust Before Applying Cavity Coater?
No. Cavity Coater requires minimal preparation: knock off any loose, scaly rust that is readily accessible and leave the rest. If grease or oil is present, clean with KBS Klean first. The one hard requirement is that the surface must be dry before Cavity Coater goes on.
What Comes Next After Cavity Coater?
Cavity Coater is the last step, not the first. Because nothing adheres over it, apply and fully cure every exterior coating before the cavity work begins.
- Step 1 — Prep and coat the outside
- Clean, etch, and coat exterior metal with the KBS 3-Step System, finishing in RustSeal.
- Step 2 — Let RustSeal fully cure
- RustSeal will not adhere to Cavity Coater, and overspray onto exterior surfaces during cavity work is normal and expected.
- Step 3 — Coat the cavities
- Spray Cavity Coater inside the enclosed areas. Cavity Coater over fully cured RustSeal causes no problem.
Read the Full Directions & TDS
Cavity Coater is a light amber liquid that passes BMS 3-23F penetration testing, shows 0 percent rust in water displacement testing, and produces no pitting on non-ferrous metals. Corrosion resistance exceeds 4,000 hours on steel under ASTM B-117, and the cured film passes low-temperature flake testing down to −60°F.
ColorLight Amber
Corrosion Resistance (ASTM B-117)Greater than 4,000 hours on steel
Compatibility (Cd, Mg, Al)Pass
Low Temp FlakingPass (to −60°F)
Penetration (BMS 3-23F)Pass
Optimal Working Temperature70°F to 80°F
Water Displacement0% Rust
Water ResistancePass
Effect on PaintNone
Effect on Non-Ferrous MetalsNo pitting
Recommended Film Thickness1 mil dry
Cleanup / Excess RemovalMineral spirits
Cavity Wax Provides Rust Protection in Hard-to-Reach Areas
Why enclosed metal cavities are the most vulnerable spots on a vehicle, and how Cavity Coater prevents long-term rust damage where other products cannot reach.
Read Article →
How To Attach The Cavity Wand to KBS Cavity Coater Aerosol
Step-by-step guide showing how to attach the Cavity Wand to the Cavity Coater Aerosol for complete 360-degree cavity coverage.
Read Article →
How To Prepare Metal Before Body Work To Prevent Future Rust
Proper metal prep before body work is what makes rust prevention last. The KBS system from bare metal to finished coat.
Read Article →
Cavity Coater Directions and Technical Data Sheet
Full application instructions for aerosol and bulk formats: surface prep, spray distance, wick time, thinning ratios, and spray gun settings.
View Directions →
KBS RustSeal: Complete Exterior Rust Protection
For maximum protection, pair Cavity Coater on the inside with RustSeal on the outside. RustSeal stops and encapsulates rust on exterior metal.
Shop RustSeal →
Cavity Coater Support Forum
Answers from the KBS technical team and other customers on Cavity Coater application, coverage, and compatibility.
Visit Forum →
Coverage rates, application methods, surface prep, and how Cavity Coater fits with the rest of the KBS system. Ready to protect your vehicle?
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KBS Cavity Coater is a single-step, super-penetrating corrosion inhibiting coating (CIC) for the inside of enclosed metal cavities. Cavity Coater wicks deep into welds and seams by capillary action, reaching surfaces that primers and topcoats cannot, and displaces water on contact so corrosion never gets started. The cured film is self-healing, closing back over itself after minor abrasion.
Cavity Coater delivers over 4,000 hours of salt spray protection per ASTM B-117 testing on steel, more than four times a conventional cavity wax. Cavity Coater also passes low-temperature flake testing to −60°F, water displacement testing at 0 percent rust, BMS 3-23F penetration testing, and compatibility testing with cadmium, magnesium, and aluminum.
Cavity Coater is used inside any enclosed or hard-to-reach metal surface: rocker panels, boxed frames, inside doors, inside fenders, windshield cowls, trunk lids, hoods, A-posts, B-posts, tailgates, and the back sides of bumpers.
Yes, Cavity Coater also works as an anti-seize. Its lubricating properties resist carbon fusion and make later disassembly easier on nuts, bolts, screws, shafts, pipe fittings, gaskets, press-fit and valve assemblies, chain drives, and general machinery.
Use the Cavity Coater Aerosol with a KBS Cavity Wand. Shake the can extremely well, push the wand onto the spray tip with a slight twist, insert it into the cavity through a 1/4-inch access hole, depress the tip, and withdraw at about one foot per second. Repeat for complete coverage, then wait 10 minutes for the coating to wick into the seams.
For bulk quart and gallon sizes, thin 30 to 50 percent with KBS #1 Thinner or mineral spirits and spray through a KBS Schutz Underseal Spray Gun with a 48-inch 360-degree wand at 90 to 150 PSI.
Cavity Coater requires minimal surface preparation. Remove any readily accessible loose, scaly rust and leave the rest. If grease or oil is present, clean the surface with KBS Klean first. The surface must be dry before application. Bare metal is not required; Cavity Coater is designed to penetrate and protect imperfect surfaces.
Do not caulk or paint over Cavity Coater. Cavity Coater is a final-step product applied to interior cavities after all exterior paints and coatings have completely cured. Topcoats will not adhere to Cavity Coater.
If you are using both RustSeal and Cavity Coater, apply and fully cure RustSeal first on the exterior, then coat the interior cavity.
Yes. Pairing RustSeal with Cavity Coater gives inside plus outside rust protection: RustSeal seals the exterior surface, Cavity Coater seals the interior cavity. Order matters. Apply and fully cure RustSeal first, then apply Cavity Coater. RustSeal will not adhere to Cavity Coater, but Cavity Coater over fully cured RustSeal is not a problem.
Coverage at 1 mil (0.001 inch) dry film thickness:
Aerosol: 125 sq. ft.
Quart (32 oz.): 200 sq. ft.
Gallon (128 oz.): 800 sq. ft.
5-Gallon Pail: 4,000 sq. ft.
55-Gallon Drum: 44,000 sq. ft.
A typical car or light truck takes one to two aerosols to treat all rocker panels, doors, and frame rails.
The Cavity Coater Aerosol with Cavity Wand works best between 70°F and 80°F. Bulk quart and gallon material should also be at room temperature before stirring and thinning. Once cured, Cavity Coater resists cracking and flaking down to −60°F, so cold-climate vehicles and equipment are not a problem.
Lightly dampen a clean, dry rag with mineral spirits (do not soak it) and wipe off any excess Cavity Coater that ran onto exterior surfaces. To clean the Cavity Wand, invert the aerosol can and spray for 10 seconds to flush residual coating out of the wand. The wand is then ready for storage or reuse.
All About KBS Cavity Coater: Designed To Stop Rust
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