There are many different marine sealants on the market and deciding which is the best choice for your application can be a bit daunting. In this post we will look at the characteristics of the various 3M marine sealants and provide recommendations for the best sealants to use on different parts of your boat.
All of the 3M marine sealants are designed for marine environments and will bond or seal wood, metal, glass, gelcoat and most plastics—including fiber-reinforced plastic (FRP).
5200
3M 5200 is the strongest of the marine grade sealants. It provides the greatest tensile strength and hardness while still maintaining flexibility to absorb shocks and structural movements. It is a high-performance polyurethane designed for permanent bonding & sealing both above and below the waterline. Typically tack-free in 48 hours and fully cured in 5-7 days, it is ideal for large surface area applications that require a long open time.
5200 FC (Fast Cure)
3M 5200 FC is a fast-cure version of 5200 which cures faster and has slightly less tensile strength and hardness than standard 5200. Like 5200, it is a high-performance polyurethane designed for permanent bonding & sealing above and below the waterline. Typically tack-free in 1 hour and fully cured in 24-48 hours, it is ideal for applications that require a fast, long-term seal.
Both 5200 and 5200 FC are a great choices for heavy-duty bonding & sealing of hull to deck seams, wood to fiberglass, marine hardware, and hull and stern joints.
4200 FC (Fast Cure)
3M 4200 FC is a fast-curing urethane that provides medium-strength bonding & sealing. It has lower tensile strength and hardness than 5200 and can be removed after prolonged used, allowing for easier disassembly of bonded parts. Typically tack-free in 1-2 hours and fully cured in 24 hours, it forms watertight, weather-resistant seals on hardware and in joints both above and below the waterline.
4000 FC UV (Fast Cure Ultraviolet)
3M 4000 FC UV is a medium-strength, UV-resistant, color-stable polyurethane that provides water-tight sealing above and below the waterline. With a tensile strength in between the 4200 and 5200 sealants and a hardness similar to 4200 FC, it can be removed if rework or disassembly is needed. Typically tack-free in less than 1 hour and fully cured in 24 hours, it is ideal for through-hull fittings and deck hardware where cosmetics are important.
3000 UV (Ultraviolet)
3M 3000 UV is a silane-modified polymer (SMP) that cures without isocyanates. With a relatively low tensile strength and hardness it is designed for cosmetic sealing where UV-resistance and low VOC (volatile organic compounds) are important. Typically tack-free in 1 hour and fully cured in 24 hours, it can be used above and below the waterline and is ideal for port hole and general cosmetic sealing.
Marine Silicone
3M Marine Silicone is a non-yellowing, mildew-resistant sealant. With a low tensile strength and hardness, it remains flexible even after years of exposure. Typically tack-free in 10 minutes, Marine Silicone is a good choice for above-waterline sealing around dashboard components and port lights.
View the following 3M brochures for additional information:
Marine Adhesives and Sealants
Marine Adhesives for Boat Owners
Homer Marine supplies all of the marine sealants reviewed here, from single 1 oz tubes up to cases of cartridges and sausage packs. Feel free to call us at (907) 435-7881 or email ericsloth@gmail.com if you have any questions about which marine sealant to use for your application.