3M Urethane Seam Sealer 08368 White 310 mL Cartridge — Flexible, Paintable, Non‑shrinking

This high-solids urethane comes in a 310 mL (10.5 fl oz) cartridge and bonds to bare metal, primed panels and painted substrates. It offers permanent flexibility, resists shrinking and cracking, and can be tooled to a fine featheredge or brushed for a neat finish. The product cures in 24 hours, becomes tack-free and paintable in roughly 30–45 minutes, and is formulated to outperform traditional solvent-based seam sealers in hot or humid conditions.

How quickly can I paint or finish after applying this seam sealer?

The sealer reaches a tack-free state and accepts paint in about 30–45 minutes under normal shop conditions. Full cure is achieved in approximately 24 hours, providing the final elastomeric properties you expect from a urethane system.

• Tack-free and paintable: 30–45 minutes
• Functional cure: 24 hours for full flexibility
• Work time: roughly 10 minutes after bead placement
• Allow longer cure in cold or very humid environments

Will this adhere to different auto surfaces and how is it applied?

Yes — the one-component formula adheres reliably to bare metal, primed metal and factory paint, giving technicians a versatile sealing option. It’s dispensed from a standard cartridge gun and can be tooled, feathered or brushed to match surrounding contours.

• Compatible with bare, primed and painted metal
• Use a standard 10.5 fl oz cartridge gun for application
• Tool or brush to blend edges or fill large voids
• Designed for industrial and occupational use only

How does this urethane seam sealer perform compared with solvent-based products?

3M’s urethane formula delivers greater elasticity and long-term durability versus solvent-based alternatives, which can shrink or crack over time. The moisture-curing chemistry also keeps the bead stable in high heat and humidity, making it suitable for demanding automotive and RV environments.

• Non-shrinking and non-cracking for long-term seals
• Maintains flexibility for dynamic joints and panels
• Performs well in hot, humid conditions thanks to moisture cure
• High-solids formulation fills gaps without excessive sagging

What should technicians know about working time and toolability?

After extrusion, you typically have about ten minutes of workable time to tool, smooth or brush the bead before it begins to skin over. Because the product can be feathered to a fine edge, it’s suitable for both structural seam filling and cosmetic finishing when matched with proper surface prep and tooling.

• Approximate work time: 10 minutes after application
• Can be feathered, tooled or brushed for a clean finish
• Best results when surfaces are clean, dry and free of contaminants
• Full mechanical properties after 24-hour cure

This cartridge is intended for professional, industrial or occupational use and is not sold for consumer DIY applications. For safety and performance, follow 3M’s product data sheet, observe shop ventilation practices, and use appropriate personal protective equipment.

Who is this for: 3M Urethane Seam Sealer 08368 is aimed at collision repair shops, RV service centers, fleet maintenance crews and industrial body shops that need a robust, flexible seam filler that accepts primer and paint quickly. It’s ideal for technicians who require a durable, moisture-curing product that fills large gaps, smooths to a featheredge, and withstands challenging environmental conditions.