Swellstop is a butyl polymer-based sealant tape. Swellstop is a water-swellable, waterproofing sealant designed for use on many types of poured-in-place and below-grade precast concrete applications. On exposure to water, it will begin to swell to seal any exposed gaps in concrete joints. Swellstop has excellent adhesion to clean, dry concrete. It is specifically intended for non-moving joints. It features an all-weather application and is engineered for use under most temperature conditions.