Composite Research, Inc.

Composite Research, Inc.
Makers of Sundance, Sea Born, and Spyder Boats

How to clean the caulk in my boat’s seams?

The “caulk” used in your CRI boat is a UV resistant, polymer sealant made specifically for permanent elastic seals.  Occasionally you may notice what appears to be mildew forming on the surface. This is actually hydrocarbons primarily from air pollution (typically auto exhaust) that forms a film on the surface of the sealant.

To clean, use mineral spirits and a soft cotton rag to scrub the sealant surface. Several applications may be required. Once clean, wash the area with a large amount of a degreasing liquid detergent (i.e. ”Dawn”) and plenty of fresh water.

Remember to use personal protective equipment such as solvent resistant gloves and protective eyewear.

Product Information

Sikaflex®-521 UV

Sikaflex®-521 UV is a multi-purpose, UV resistant, non-sag, elastic, one-part silane-terminated polymer sealant, which cures on exposure to atmospheric moisture to form a durable elastomer. Sikaflex-521 UV is solvent and isocyanate free.


Sikaflex®-521 UV bonds well to a wide variety of substrates without the need for special pre-treatment and is suitable for making permanent, high strength elastic seals. Compatible substrate materials include wood, metals, (particularly aluminum including anodized components), sheet steels (including phosphated, chromated and zinc-plated components), metal primers and paint coatings (two-part systems), ceramic materials, fiberglass, plastics and glass.

Characteristics and Advantages
  • Very low VOC/solvent free
  • Silicone and PVC-free
  • Isocyanate-free
  • High electrical resistance
  • Resistant to aging and weathering

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