3M 08027 Marine Grade Silicone Sealant White 10 oz Cartridge | Mildew & High-Temp Resistant | Non-Yellowing | Removable | Above Waterline Trim, Hatches, Drip Rails & Moldings

3M 08027 Marine Grade Silicone Sealant White 10 oz Cartridge — Mildew & High-Temperature Resistant | Non-Yellowing | Flexible & Removable | Above Waterline Trim, Hatches, Drip Rails & Moldings | Skin Time 5–10 Min, Full Cure ~24 Hours

3M Marine Grade Silicone Sealant White (08027) is a marine-formulated silicone sealant designed for above-waterline sealing of trim, hatches, drip rails, and moldings on gel coat, fiberglass, wood, glass, metal, rubber, and vinyl. Mildew resistant and high-temperature resistant. Remains flexible after cure. Non-yellowing. Removable — silicone seals can be cut away for hardware removal without damage to bonded surfaces. Skin time 5–10 minutes; full cure approximately 24 hours. White. 10 oz cartridge for standard caulking gun. Above waterline use only. Non-paintable — paint will not adhere to cured silicone.

Part Specifications

• Part Number: 3M-08027
• Product Line: 3M Marine Grade Silicone Sealant
• Color: White
• Size: 10 oz cartridge (requires standard caulking gun)
• Chemistry: Silicone
• Application Zone: Above waterline only — not rated for below-waterline use
• Substrates: Gel coat, fiberglass, wood, glass, metal, rubber, vinyl
• Typical Applications: Trim, hatches, drip rails, moldings, port lights, deck hardware above the waterline
• Cured Properties: Flexible, mildew resistant, high-temperature resistant, non-yellowing, removable
• Paintability: Non-paintable — paint will not adhere to cured silicone; do not use where the sealant bead will be painted over
• Skin Time: 5–10 minutes
• Full Cure Time: Approximately 24 hours

Silicone vs Polyurethane — Choosing the Right Marine Sealant

The 08027 is a silicone sealant. Most other 3M marine sealants in this catalog are polyurethane (5200, 4200FC, 4000 UV). These are chemically different and suited for different applications:

• Silicone (this product — 08027): Above waterline only. Excellent mildew resistance and high-temperature resistance. Flexible, non-yellowing, serviceable (removable). Bonds to a wide range of substrates including rubber and vinyl that polyurethane may not bond to as effectively. Non-paintable — cured silicone repels paint. Best for trim, hatches, port light frames, drip rails, vent covers, and other above-waterline fittings where the sealant bead will remain exposed and visible.
• 3M Marine Adhesive Sealant 4200FC (06560 White 10 oz): Polyurethane, strong serviceable bond. Above and below the waterline. Paintable. For through-hulls, rub rails, stern joints, and deck fittings where below-waterline rating, paintability, or higher bond strength is needed.
• 3M Marine Adhesive Sealant 5200 (06500 White 10 oz): Polyurethane, permanent bond. Above and below the waterline. Paintable. For structural permanent bonds that will never be disassembled.
• 3M Marine Adhesive Sealant 4000 UV (06580 White 10 oz): Polyurethane, medium strength serviceable. Above waterline only. UV resistant. Paintable. For UV-exposed above-waterline hardware where paintability and UV resistance are priorities.
• When silicone is the right choice: Rubber and vinyl substrate bonding, mildew-prone areas such as hatches and trim channels, high-temperature areas such as exhaust cover plates and engine compartment trim, and any above-waterline application where the exposed sealant bead must remain flexible and non-yellowing over extended sun exposure.

Non-Paintable — Critical Consideration Before Applying

• Cured silicone repels paint — any paint, primer, topcoat, or gel coat applied over cured silicone will not adhere and will peel or fish-eye
• Do not use the 08027 in any joint, seam, or fitting location where the sealant surface or surrounding area will be painted or topcoated after application
• If the area around a fitting has been contaminated with silicone (from a previous repair or other silicone product), the surface must be fully cleaned and decontaminated before painting — silicone contamination is one of the most common causes of paint adhesion failure in marine refinishing
• For above-waterline fittings that will be painted over, use a paintable polyurethane sealant such as 3M 4000 UV (06580) instead
• If you are unsure whether a surface has been previously sealed with silicone, apply a test drop of water — silicone contamination causes water to bead tightly; a clean, decontaminated surface will sheet water

Application Notes

• Requires a standard 10 oz caulking gun (not included)
• Surfaces must be clean, dry, and free of old sealant, grease, oil, wax, and loose material before applying; wipe with isopropyl alcohol and allow to dry
• Apply in a continuous bead; tool the bead with a wet finger or plastic tool within the 5–10 minute skin time window — once the surface skins over, the bead cannot be tooled or smoothed without tearing
• Moisture and atmospheric humidity cure the silicone — higher humidity accelerates cure; cooler, drier conditions slow it
• Full cure approximately 24 hours — do not stress the joint or expose to standing water at the seam until fully cured
• To remove cured silicone: score the bead edge with a razor blade and peel; residue can be cleaned with a silicone remover or isopropyl alcohol. Thoroughly remove all silicone residue from any surface that will be painted
• Wear gloves — uncured silicone is messy and difficult to remove from clothing and porous surfaces

Additional Information

• Vendor: 3M
• SKU: 3M-08027
• Product Type: Boat & Engine Maintenance / Adhesives & Sealants
• Color: White
• Size: 10 oz cartridge
• Country of Origin: USA
• HS Code: 3910.00 (silicones in primary forms — cured silicone sealant in cartridge may classify under 3214 or 3910; verify for your import classification)

Frequently Asked Questions

Q: Can the 08027 be used below the waterline?
A: No — the 08027 is rated for above-waterline use only. For below-waterline sealing, use a polyurethane sealant rated for below-waterline use: 3M 4200FC White 10 oz (06560) for serviceable bonds or 3M 5200 White 10 oz (06500) for permanent structural bonds.

Q: Can I paint over the 08027 after it cures?
A: No — the 08027 is non-paintable. Cured silicone repels paint; any topcoat, primer, or gel coat applied over cured silicone will not adhere and will peel or fish-eye. For above-waterline fittings that will be painted, use a paintable polyurethane sealant such as 3M 4000 UV (06580) instead.

Q: What is the difference between the 08027 silicone sealant and 3M 4200FC?
A: Different chemistries for different applications. The 08027 is silicone — above waterline only, non-paintable, mildew and high-temperature resistant, bonds rubber and vinyl. The 4200FC (06560) is polyurethane — above and below waterline, paintable, stronger adhesive bond. Use silicone for trim, hatches, and drip rails where mildew resistance and flexibility are priorities and the bead will not be painted; use 4200FC where below-waterline rating, paintability, or higher bond strength is needed.

Q: How long before I can get the boat wet after applying?
A: Full cure is approximately 24 hours. Above-waterline applications (trim, hatches, drip rails) can be exposed to rain and spray after full cure. Do not submerge the joint or expose to standing water at the seam until fully cured.

Q: Is the 08027 removable if I need to replace a hatch or fitting later?
A: Yes — silicone is removable. Score the cured bead edge with a razor blade, peel, and clean residue with silicone remover or isopropyl alcohol. Silicone does not bond as permanently as polyurethane — fittings sealed with the 08027 can be removed for maintenance and replacement without cutting or grinding.