3M 08029 Marine Grade Silicone Sealant Clear 10 oz Cartridge | Mildew & High-Temp Resistant, Removable, Non-Paintable | Above Waterline Trim, Hatches, Drip Rails & Moldings

3M 08029 Marine Grade Silicone Sealant Clear 10 oz Cartridge — Mildew & High-Temperature Resistant, Removable Above-Waterline Sealant for Trim, Hatches, Drip Rails & Moldings on Gel Coat, Fiberglass, Wood, Glass, Metal, Rubber & Vinyl

3M Marine Grade Silicone Sealant is designed for the harsh marine environment and formulated to be mildew resistant and high-temperature resistant. Seals gel coat, fiberglass, wood, glass, metal, rubber, and vinyl surfaces. Remains flexible after cure, does not yellow, and is removable for future service. Clear color maintains a clean appearance on exposed seams and joints. Skin time 5–10 minutes, full cure in approximately 24 hours. Above waterline use only. Non-paintable — paint does not adhere to cured silicone. 10 oz cartridge for use with a standard caulking gun.

Part Specifications

• Part Number: 3M-08029
• Color: Clear
• Size: 10 oz cartridge (caulking gun)
• Chemistry: Silicone
• Bond Type: Removable
• Substrates: Gel coat, fiberglass, wood, glass, metal, rubber, vinyl
• Typical Applications: Sealing trim, hatches, drip rails, moldings
• Waterline Use: Above waterline only
• Paintable: No — non-paintable; paint does not adhere to cured silicone
• Mildew Resistance: Yes
• High-Temperature Resistance: Yes
• Yellowing: Non-yellowing
• Flexibility: Remains flexible after cure
• Skin Time: 5–10 minutes
• Full Cure Time: Approximately 24 hours

Silicone vs Polyurethane Sealant — Choosing the Right Chemistry for the Application

The two primary sealant chemistries used in marine applications are silicone and polyurethane. They are not interchangeable — each has specific strengths and limitations that determine the correct choice for each application:

• Silicone sealant (3M-08029 — this product):
  • Removable after cure — can be cut and peeled from most surfaces for future service or replacement without damaging the underlying substrate
  • High-temperature resistant — silicone handles heat better than polyurethane, making it suitable for applications near engines, exhaust, or other heat sources
  • Mildew resistant — silicone resists mildew growth on the sealant surface, suitable for interior seams and areas that trap moisture
  • Non-yellowing — maintains a clear appearance on exposed seams and joints without discoloring over time from UV exposure
  • Wide substrate compatibility — seals gel coat, fiberglass, wood, glass, metal, rubber, and vinyl
  • Above waterline only — not recommended for below-waterline sealing
  • Non-paintable — silicone-contaminated surfaces will cause paint adhesion failures (fish-eye); do not apply over or adjacent to surfaces that will receive paint
  • Best applications: trim, hatches, drip rails, moldings, interior seams, port light seals, and above-waterline sealing where removability, mildew resistance, and high-temperature resistance are priorities
• Polyurethane sealant (3M 5200 / 4200 series):
  • 5200 (3M-05203): Permanent bond — above and below waterline; bonds wood, gel coat, fiberglass; structural applications; extremely difficult to remove after cure
  • 4200: Serviceable bond — above and below waterline; bonds gel coat, fiberglass, wood, metal; through-hulls, deck hardware, hatches; can be removed for service
  • Paintable after cure — polyurethane sealants can be painted over when fully cured
  • Not high-temperature resistant in the same range as silicone

Key decision rule: Use silicone (08029) for above-waterline applications where removability, mildew resistance, high-temperature resistance, or wide substrate compatibility (especially rubber, vinyl, and glass) are needed, and where paint will not be applied after sealing. Use polyurethane (4200 or 5200) for below-waterline sealing, structural bonding, and applications where painting after sealing is required.

Application Notes

• Requires a standard caulking gun — cut the cartridge tip at a 45° angle to the desired bead size before loading
• Surface preparation: surfaces must be clean, dry, and free of grease, wax, oil, and loose material; clean with isopropyl alcohol and allow to dry before applying
• Apply a continuous bead and tool to the desired profile within the skin time window — skin time is 5–10 minutes; in warm or humid conditions, tooling time is shorter
• Do not apply in wet conditions or on wet surfaces; moisture affects silicone cure quality on some substrates
• Full cure in approximately 24 hours; joint can be exposed to water and normal use after full cure
• Non-paintable warning: Do not apply silicone where the sealed surface or adjacent area will receive paint. Silicone contamination — even from handling with silicone-contaminated gloves — causes fish-eye and adhesion failure in paints and coatings. If the area will eventually be painted, use a polyurethane sealant (3M 4200) instead
• Above waterline only: Do not use below the waterline. For through-hulls and below-waterline sealing, use 3M Marine Adhesive Sealant 4200 or 5200
• Cleanup: uncured silicone can be removed with isopropyl alcohol or mineral spirits; cured silicone must be cut and peeled for removal

Additional Information

• Vendor: 3M
• SKU: 3M-08029
• Product Type: Boat & Engine Maintenance / Adhesives & Sealants
• Color: Clear
• Size: 10 oz cartridge
• Country of Origin: USA
• HS Code: 3214.10 (glaziers' putty, grafting putty, resin cements, caulking compounds — verify for your import classification)

Frequently Asked Questions

Q: Can this silicone sealant be used below the waterline?
A: No — 3M Marine Grade Silicone Sealant is rated for above waterline use only. For below-waterline sealing including through-hulls, keel bolts, and hull fittings, use 3M Marine Adhesive Sealant 4200 (serviceable) or 5200 (permanent).

Q: Can I paint over this silicone sealant after it cures?
A: No — this product is non-paintable. Cured silicone repels paint and causes adhesion failures (fish-eye) in any paint or coating applied over it. Even silicone residue on adjacent surfaces from tooling or handling can cause paint adhesion failures across a wider area. If the sealed area or surrounding surfaces will be painted, use a polyurethane sealant (3M Marine Adhesive Sealant 4200) which is paintable after full cure.

Q: What is the difference between this silicone sealant and 3M 4200 or 5200?
A: Different chemistries for different applications. This silicone sealant is removable, non-paintable, high-temperature resistant, mildew resistant, compatible with rubber and vinyl, and rated for above waterline use only. 3M 4200 and 5200 are polyurethane sealants — 4200 is serviceable (removable) and 5200 is permanent; both are paintable after cure and rated for above and below waterline use. Use silicone for trim, hatches, drip rails, rubber and vinyl seals, and above-waterline joints where removability and temperature resistance are needed. Use 4200 or 5200 for structural bonding, through-hulls, and applications where paint will be applied after sealing.

Q: What surfaces does this product seal?
A: Gel coat, fiberglass, wood, glass, metal, rubber, and vinyl. The wide substrate compatibility — particularly rubber, vinyl, and glass — makes it suitable for port light seals, hatch trim, and applications that involve mixed materials.

Q: How do I remove cured silicone sealant if I need to service a joint?
A: Score the cured silicone bead with a utility knife or silicone removal tool and peel it away from the surface. A plastic scraper helps remove the bulk. Residual silicone film on the surface can be removed with a silicone remover solvent or by careful scrubbing with a nylon abrasive pad and isopropyl alcohol. Thoroughly remove all silicone residue from any surface that will be re-sealed or painted after removal.