Sailboats USA 🇺🇸

3M 5200 Marine Adhesive Sealant

Type: One-part polyurethane adhesive/sealant

Bond strength: Extremely high — one of the strongest marine sealants made. Bonds fiberglass, wood, metal. Once fully cured (5–7 days), it is essentially permanent.

Flexibility: Moderate — flexible enough to handle hull movement but stiff enough to hold structural joints.

Waterproof: Yes — above and below waterline.

Paintable: Yes, after full cure.

Removal: Extremely difficult. Requires mechanical cutting, chisels, and chemical remover (Un-Hesive). Plan to damage the substrate.

Also available: 3M 5200 Fast Cure — same strength, sets in 24 hrs vs. 5–7 days. Same warnings apply.

USE FOR: Hull-to-deck joints, keel bolt bedding, through-hull fittings below waterline, structural bonding where permanence is acceptable. Anywhere you intend it to be there forever.

DO NOT USE FOR: Deck hardware you ever plan to remove, portlights, hatches, or any fitting you will need to service.

3M 4200 Marine Adhesive Sealant

Type: One-part polyurethane adhesive/sealant

Bond strength: Strong — significantly less than 5200 but still a robust sealant with good adhesion. Designed to be removable with reasonable effort.

Flexibility: Good — excellent for joints that move, flex, or expand/contract with temperature.

Waterproof: Yes — above and below waterline.

Paintable: Yes, after cure.

Removal: Workable with plastic scrapers and solvent — does not require a grinder.

Also available: 3M 4200 Fast Cure.

USE FOR: Bedding deck hardware (cleats, stanchion bases, chainplates, winch bases), portlights and opening ports, hatches, keel-stepped mast partners, rubrails, deck plates. The best all-around choice for most deck hardware bedding on a sailboat.

DO NOT USE FOR: Anything that must be truly structural or permanently bonded underwater.

Sikaflex 291

Type: One-part polyurethane adhesive/sealant

Bond strength: Similar to 3M 4200 — strong sealant, serviceable bond. Sikaflex products are the standard choice when bonding to aluminum (where 5200 and 4200 are less effective on metal).

Flexibility: Excellent — highly elastic, handles significant movement.

Waterproof: Yes — above and below waterline.

Paintable: Yes.

USE FOR: Bedding stainless steel stanchion bases, aluminum deck hardware, aluminum toe rails, portlights, hatches, any application involving metal-to-fiberglass joints. The preferred alternative to 4200 when metal is involved.

DO NOT USE FOR: Structural bonding requiring maximum strength — use 292 for that.

Sikaflex 292

Type: One-part high-strength polyurethane structural adhesive

Bond strength: Extremely high — Sika's equivalent to 3M 5200. Particularly effective on metal substrates where 5200 can fail. Dries faster than 5200.

Flexibility: Moderate.

Waterproof: Yes — above and below waterline.

USE FOR: Structural bonding of metal fittings, aluminum spars, keel bolts, highly loaded through-deck fittings, any structural joint involving metal. Use where 5200 would be chosen but metal is the substrate.

DO NOT USE FOR: Anything you plan to service or remove.

BoatLIFE Life-Calk

Type: Polysulfide sealant

Bond strength: Moderate — primarily a sealant, not a structural adhesive. Remains very flexible permanently.

Flexibility: Outstanding — polysulfide stays flexible longer than polyurethanes in high-UV environments.

Chemical resistance: Excellent — resistant to diesel fuel, oils, and solvents. The only common marine sealant that holds up in fuel fills and around engine areas.

Compatible with teak: Yes — polysulfide does not break down from teak's natural oils and resins, unlike polyurethanes.

Paintable: Yes.

Removal: Easier than polyurethanes — can be cut and peeled with reasonable effort.

USE FOR: Teak deck seams (the correct sealant for traditional teak decks), fuel deck fills and fuel vents, diesel and fuel system fittings, bedding wooden deck hardware, seacocks on wooden boats, any seam near diesel fuel. Classic choice for traditional boatbuilding.

DO NOT USE FOR: Bonding to most plastics, EPDM, or neoprene (polysulfide attacks these materials).

BoatLIFE Life-Seal

Type: Silicone-modified sealant

Bond strength: Moderate. Top performer in adhesion tests across a wide range of surfaces including most plastics — broader substrate compatibility than most marine sealants.

Flexibility: Excellent.

Paintable: No — silicone-modified; will prevent paint adhesion.

USE FOR: Plastic portlights and windows where paintability is not required, bedding where broad substrate compatibility is needed.

DO NOT USE FOR: Any surface that will be painted. Below waterline.

Dow Corning / 3M Marine Silicone

Type: Silicone sealant

Bond strength: Low to moderate. Permanently contaminates surfaces — nothing will bond over it.

USE FOR: Interior non-marine plumbing only (sink drains, freshwater fittings below countertops). That is all.

DO NOT USE FOR: Any deck hardware, portlights, hatches, hull fittings, or any surface that may ever be painted or rebedded. A single application of silicone will cause paint fish-eyes and adhesion failures on that surface indefinitely.

Butyl Tape

Type: Non-curing butyl rubber tape

Bond strength: Low — it is a gasket, not a structural adhesive. Relies on mechanical fastener clamping to seal.

Flexibility: Permanent — never hardens, never cures, stays pliable indefinitely.

Removal: The easiest of all marine sealants — peels cleanly without solvents or scrapers.

USE FOR: Bedding deck hardware with mechanical fasteners (cleats, blocks, winches, stanchion bases, chainplates) where the fastener does the holding and the sealant only prevents water intrusion. The preferred choice for DIYers who want to be able to re-bed hardware in the future without a fight. Does not work for structural bonding or irregular gaps.

DO NOT USE FOR: Below waterline. Structural bonding. Large gaps.