What They Do

Since the whole point of a boat is to seal the water out, it's no wonder that sealant products find wide application aboard. The three primary functions of sealants are: 

1. To form a water/air-tight seal between two or more pieces.
2. As an adhesive to join two or more pieces (often used in conjunction with mechanical fasteners.
3. To isolate one piece from another (to prevent electrolysis, noise, etc.)

How They Work

Sealants compounds cure to a tough, flexible, rubbery consistency. They adhere to surfaces to prevent water or air from penetrating. Unlike epoxies or glues, sealants remain permanently flexible so they can withstand some movement of the surfaces to which they are bonded without cracking or losing adhesion.

How They Differ

There are three primary sealant formulas commonly used in marine applications. Here's how they stack up:

1. Polysulfides One of the most versatile sealants available. Two-part polysulfides have long been popular as a caulking material for teak decks. One-part polysulfides are easier to use and just as durable, but slower to cure. Bonds well to most surfaces. Oily woods (such as teak) should be primed before using polysulfide. It should not be used on plastic as it will melt it.

2. Polyurethanes recommended for permanent bonding because of its enormous adhesion. Good for hull/deck joints and bonding through hull fittings. It is incompatible with ABS and Lexan plastic.

3. Silicone Very elastic and highly chemical-resistant. Makes an excellent insulating barrier between dissimilar metals. Not as strong in adhesive strength as polysulfide or polyurethane. Compatible with plastics.
 
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