Sika Thoroseal 581 – Waterproof Cement-Based Coating (50 lb Bag) (Formerly MasterSeal 581)

Sika Thoroseal 581 (formerly MasterSeal 581) is a polymer-modified, cement-based coating for concrete and masonry that provides a durable waterproof and air-barrier finish. It’s formulated to resist both positive and negative hydrostatic pressure — making it ideal for waterproofing foundations, basements, retaining walls, water-treatment structures, cisterns, and other below-grade or exterior masonry surfaces.

The coating remains breathable, allowing interior moisture to escape without damaging the barrier, and can be applied to vertical and light-pedestrian horizontal surfaces. Available in multiple standard and custom colors, Sika Thoroseal 581 also helps improve the appearance of architectural concrete while sealing pores and minor imperfections for a maintenance-free finish.

Benefits

• Waterproof and air-barrier performance — protects interiors from dampness and moisture damage
• Withstands positive and negative hydrostatic pressure — suitable for below-grade, foundation, and water-retaining applications
• Breathable cure allows vapor escape while maintaining barrier integrity
• Compatible with architectural coatings and textured finishes — improves surface appearance
• Available in multiple standard landscape colors and custom color options for design flexibility
• Suitable for interior and exterior, above- and below-grade applications