See full version: What is the best sealant for thru hull fittings
The terms “caulk” and “sealant” are often used interchangeably, since both are used to fill joints and seams. The biggest difference between caulk and sealant is elasticity. Caulk is more rigid than sealants when dry. Sealants hold up better in spaces that are prone to a lot of expansion and contraction.
Coat-It Epoxy Sealer with Kevlar is a waterproof epoxy sealer for aluminum, steel, fiberglass, wood, and concrete. You can apply this sealer with a brush, roller, or squeegee. The ten mils prime coat is flexible and non-shrinking in one application. It has a pot life of 30 minutes.
Flex seal does work as a temporary fix for small leaks in a jon boat. However, it should not be used as a permanent solution for a leaking boat.
Polyurethane: Recommended for permanent bonding because of its enormous adhesive strength of about 700psi, polyurethane is more of an adhesive than a sealant. It is good for hull/deck joints and bonding thru-hull fittings but incompatible with ABS and Lexan, and does not adhere well to many other types of plastic.
Clean the fiberglass with soap and warm water. Rinse the fiberglass with clean water to remove soap residue and let dry. Rub the surface with a polishing compound to take off the oxidized layer. Polishes have abrasives in them and will act like fine sand paper.
When selecting a sealant, these properties are typically the most important:
Polyurethane: Recommended for permanent bonding because of its enormous adhesive strength of about 700psi, polyurethane is more of an adhesive than a sealant. It is good for hull/deck joints and bonding thru-hull fittings but incompatible with ABS and Lexan, and does not adhere well to many other types of plastic.
When selecting a sealant, these properties are typically the most important: more
Flex seal does work as a temporary fix for small leaks in a jon boat. However, it should not be used as a permanent solution for a leaking boat. here
Marelon plastic thru hulls are coast guard approved for use below the water line and bronze or SS needs to be isolated from the aluminum below the water line. more
Agree,Either one will work fine but the 5200 is stronger.
If it is something you may want to remove one day then use the 4200.
I know its one in a million..but if your going to replace a through hull fitting below the waterline then why not make it bronze ( or another metal ) ? [links]
IMHO..use metal ( SS. or Bronze coated ) will work better if your going to replace them.
Polysulfide is a synthetic rubber compound and is the “workhorse” of marine sealants. A polysulfide sealant will adhere to joint materials well, but will allow for movement due to temperature or load. It will attack plastics (but not Marelon, epoxy or Delrin). It’s sometimes sold under the trade name “Thiokol”. It can be sanded and painted after it cures (typically 14-21 days). It can be used below the waterline and is good for thru-hull fittings and fixing deck hardware.
Silicone is a gasket material, not a sealant. Its adhesive properties are minimal and should be disregarded. It is great for insulating dissimilar metals such as stainless steel and aluminum and for any above the waterline joint that needs to be dismantled periodically. It is not possible to paint silicone. Up until recently it was the only material you could use to bed plastic (portlights etc.) more
Two part polysulfide sealant is used to caulk teak decks.
Marine silicone rubber sealant by BoatLife
Marine grade silicone sealant by 3M
Bostik 9732 RTV silicone by Bostik
Marine silicone sealant by West Marine more