SikaFlex 1a is the professional standard for sealing foundation cracks, expansion joints, and penetrations that let water into basements and crawlspaces. Unlike hydraulic cement or epoxy, SikaFlex is a polyurethane elastomer — it remains permanently flexible after curing, accommodating the seasonal movement of foundations without re-cracking. A single tube covers cracks up to 1/2 inch wide and 1/2 inch deep with a single application. It adheres to concrete, masonry, wood, metal, and most substrates without primers on dry surfaces. The weathergrade formulation is rated for exterior use and holds up to UV, freeze-thaw cycles, and direct water exposure. Used by waterproofing contractors on foundations, window wells, pipe penetrations, and below-grade joints.

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