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Selecting a Sealant »
By Paul Esterle — Fall
2004
Polyurethanes: Among the most aggressive adhesives in the sealant world, these are best used where the fitting involved will never be removed, typically below-the-waterline through-hulls. Removing the fitting may well damage the gelcoat. Not recommended for bedding deck hardware.
Examples: 3M5200,
3M4200, Sikaflex-291
Polysulfides: Good sealant characteristics combined with good adhesive performance make this class of sealants one of the most versatile. Bonds well but can be removed without damage to the gelcoat. Highly recommended for bedding deck hardware.
Examples: 3M101,
BoatLife’s Life-caulk
Silicones: Silicones are not good bonding agents. As such, they seal best when under compression. Because they don’t bond well, they are ideal for fittings that are removed and replaced regularly. Also compatible with most plastics. Okay for bedding deck fittings when it can be compressed to form a gasket-like seal.
Examples: 3M
Marine-Grade Mildew-Resistant Silicone Sealant, Boat Life Sandable Silicone
Sealant
Polyethers: A relatively new class of adhesive/sealant, their best quality is resistance to yellowing from UV rays. They fall somewhere between polyurethanes and polysulfides in bond strength. Also recommended for use with plastics. Okay for bedding deck hardware when the sealant will be exposed to UV rays.
Examples: 3M4000
UV
The bottom line: 3M101 or BoatLife’s Life-Caulk are your best all-around choices for bedding deck hardware.
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