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  • Sikaflex 291

    Sikaflex 291

    Sikaflex 291 is an all purpose marine adhesive / sealant that is used for bedding and light...

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    Price: $13.99
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Marine Caulk and Adhesive Sealants Explained

The majority of marine-specific sealants are one of three material types: Polysulfide; Polyurethane; and Silicone. A fourth kind of sealants are hybrid silicone and polyurethane compounds that provide benefits of both materials.

In addition, there are application-specific teak deck caulking product designed to fill the grooves between teak planks on boat decks. Lastly, there is a group of items associated with traditional wooden boatbuilding, and designed for caulking wood planking seams both above and below the waterline. Examples of classic wooden boat caulk items include Oakum, Caulking Wick, Caulking Cotton, Caulking Irons, Bedding Compounds, Seam Compounds, and Seam Cement.

Choosing the correct type of adhesive or sealant is easy once the application, materials to be bonded and the sealant characteristics are understood.

Polysulfide Caulk

Items and Brands: Boatlife Life Calk

  • Where to use: Polysulfide sealants are ideal for teak decks, bedding deck and hull hardware, sealing thru-hull fittings, and underwater seams. They bond to fiberglass, wood, metal, glass, and themselves.
  • Do not use for: Bedding plastic windshields, plastic portlights (acrylic aka Plexiglas; or polycarbonate aka Lexan), bedding plastic marine fittings made from ABS or PVC.
  • Cure time: Can take a week or more to fully cure.
  • Waterline: Use above and below the waterline.
  • Chemical Resistance: Excellent resistance to teak oils, gasoline, and diesel fuel.

Polysulfide caulk is a one-part synthetic rubber material that makes a very versatile marine sealant. This type of caulk will bond readily to fiberglass, wood, metals, glass, and to itself. Polysulfide cures to a firm flexible rubber seal with excellent waterproofing and adhesion qualities. It can be applied underwater for emergency repairs, and or on damp surfaces. Please note: The solvents contained in polysulfide sealants may chemically react with and degrade many plastics, and this why they are not to be used on ABS, PVC, acrylic and polycarbonate materials as noted above.

Polyurethane Adhesive Sealants

Items and Brands: 3M 5200, 3M 5200 Fast Cure, 3M 4200 Fast Cure; Sikaflex 201US, 252, Sika-292, Sika-296, Sika-295UV, Sika-521UV, Sika-291, Sika-221

  • Where to use: Polyurethanes are ideal for thru-hull fastening, and best choice for hull-to-deck joints, deck fittings, railings and transducers. They bond tenaciously to fiberglass, wood, metal, and glass.
  • Do not use for: Bonding parts that may require disassembly in the future, as Polyurethanes are generally permanent. Do not use to bed plastic windshields, plastic portlights (acrylic aka Plexiglas; or polycarbonate aka Lexan).
  • Cure time: A week or less.
  • Waterline: Used above and below the waterline.
  • Chemical Resistance: Teak cleaners can degrade the sealant and compromise its strength.

Polyurethane adhesives form an extremely strong bond while retaining flexibility and strength above or below the waterline. Watertight bonding / sealing of fiberglass, gelcoat and wood. Alcohol should not be used when preparing surfaces for bonding as it will stop the curing process and cause the adhesive to fail. Polyurethane is not recommended for use as a teak deck seam sealer. Extended exposure to chemicals (teak cleaners, oxalic acid, gasoline, strong solvents and other harsh chemicals) may cause permanent softening.

Marine Silicone Sealants

Items and Brands: 3M Marine Grade Silicone Sealant; Boatlife Marine Silicone Rubber

  • Where to use: Head plumbing applications, interior & exterior wood, trim sealing and as a gasket adhesive.
  • Do not use for: Silicone Sealant is not recommended for the installation of glass, polycarbonate (Lexan) or acrylic (Plexiglas) windows that are not also mechanically fastened. Do not use silicone on any surface to be painted.
  • Cure time: A day or less.
  • Waterline: Used above the waterline only.
  • Chemical Resistance: Unaffected by most chemicals.

Marine Silicone sealants are mildew resistant, non-sagging, moisture curing products, suitable for above the waterline applications only. Marine Grade Silicones remain flexible with excellent resistance to the corrosive effects associated with salt, dirt, spray, and moisture. Silicone adheres to bare and painted metal, glass, fiberglass, non-oily woods, many plastics and abraded rubber. Silicone sealants typically set in a few minutes while reaching full cure in a day.

Teak Deck Caulk

Items and Brands: TDS Teak Deck Caulking; Maritime Teak Deck Caulk

  • Where to use: Caulking teak deck seams.
  • Do not use for: Anything else
  • Cure time: Up to two weeks.
  • Waterline: Used above the waterline only.
  • Chemical Resistance: Excellent.

Teak deck caulks are typically one-part, neutral curing, adhesive sealants specially formulated for caulking teak decks with outstanding adhesion to teak and other naturally oily woods. When used as directed, no primer is necessary. The caulk cures when exposed to moisture in the air to form a tough, flexible, solid rubber seal with excellent temperature stability and resistance to chemicals, sunlight, UV and water. Teak deck caulks are non-corrosive to all substrates and can be sanded when cured.

Traditional Wooden Boat Caulk

Items and Brands: Oakum, Caulking Wick, Caulking Cotton, Caulking Iron, Dolfinite Bedding Compound, Pettit Seam Compound, Interlux Boatyard Bedding Compound, Davis Slick Seam

  • Where to use: Hand Caulking or planked boat seams.
  • Do not use for: Anything else.
  • Cur etime: N/A
  • Waterline: Used above and below the waterline.
  • Chemical Resistance: N/A

Traditional wooden boats are constructed and maintained with these 'old time' products. The caulking on wooden vessels uses fibers of cotton, and oakum. These fibers are driven into the wedge-shaped seam between the planks with a caulking mallet and a broad chisel-like tool called a caulking iron. The caulking is then covered with a seam compound in the case of hull seams, or else in deck seams with melted pine pitch, in a process referred to as paying. Modern marine sealants are frequently used now in place of the pitch, or even to supplant the oakum and cotton.


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