There is a bewildering array of sealants available at your chandlers for jobs requiring a watertight seal or bond between surfaces.
Attaching deck hardware, repairing the inflatable dinghy, making a hull to deck seal, fitting portlights or sealing through-hulls and seacocks all require sealants with special qualities.
Here’s a brief run through of what’s available and what it’s good for:
These are easy-to-use and generally clean products with a variety of uses such as isolating dissimilar metals and for sealing wood, glass and most plastics. Silicone resists most boaty chemicals. Not recommended for underwater tasks such as sealing through hulls or for really tough jobs like hull to deck joints. A bit wimpy on the adhesive front.
For sealing electrical and coax cable connections you can get non-adhesive silicone compression tape that self-amalgamates into a blob of silicone after application – Bandit tape is an example. Also great for temporarily sealing leaks in water pipes, sealing rope ends , covering turnbuckles and other boatly duties. Very handy to have in the boat’s toolbox.
Polysulphide (polysulfide). Fantastically versatile and strong, stays flexible, bonds well to most surfaces and can be used above or below the waterline. Not suitable for bonding plastics – melts acrylics and some plastics such as ABS and polycarbonates such as Lexan. (Yikes!)
Takes ages to cure.