SealBoss® SwellCaulk™ – Caulk-Grade Swelling Waterstop for Cold Joints and Concrete Sealing

An Overview of SealBoss SwellCaulk

In concrete construction, water intrusion is one of the most persistent threats to structural durability and performance. Construction joints, cold joints, and pipe penetrations are particularly vulnerable to leakage, especially in below-grade, submerged, or high-moisture environments. Enter SealBoss SwellCaulk™—a next-generation, high-performance caulk-grade swelling waterstop developed specifically to combat these challenges.

What is SealBoss SwellCaulk?

SealBoss® SwellCaulk is a single-component, polyurethane-based, hydrophilic waterstop and leak-sealing caulk grade swelling waterstop paste designed for easy application and long-lasting waterproofing. The product is engineered to react with water by expanding up to 350% of its original volume, effectively sealing gaps and voids in concrete joints.

• Single-component system – no mixing required
• Water-activated expansion for maximum sealing power
• Extremely adhesive – bonds to concrete, even when rough or damp
• Flexible and moldable to irregular joint surfaces

Packaging Formats for On-Site Versatility

SealBoss SwellCaulk is available in two user-friendly packaging formats:

• Cartridges – For use with standard caulking guns
• Sausages – For use with common sausage-style applicator guns

These application options allow field teams to adapt to specific project conditions and scale—from small detailing work to long joint runs on large concrete slabs or walls.

How SwellCaulk Works: Hydrophilic Expansion and Active Sealing

The core innovation behind SwellCaulk lies in its hydrophilic polyurethane composition. Upon exposure to water, this Caulk Grade Swelling Waterstop undergoes a controlled expansion, growing up to 3.5 times its initial volume while creating a permanent compression seal. This physical expansion enables the product to fill gaps and irregular surface areas, forming a dense, resilient, and water-impermeable seal.

• Self-adheres to dry or moist concrete
• Eliminates need for primers or adhesives
• Adapts to rough, porous, or irregular substrates
• Forms watertight seals even in uneven joints

SwellCaulk as a Pressure-Positive Compression Seal

Unlike conventional caulks that merely sit in a joint, SwellCaulk becomes an active barrier once confined and hydrated. Its expansion creates a compression seal, pressing outward against joint walls to establish a pressure-positive seal—blocking water flow even under significant hydrostatic pressure.

• Withstands considerable hydrostatic pressures
• Provides permanent, resilient water sealing
• Ideal for below-grade, wet, or submerged conditions

Understanding Cold Joints—and Why They Need SwellCaulk

Cold joints form when a new batch of concrete is poured next to an existing pour that has already begun to set. These unbonded seams can act as fine channels for water migration, creating long-term leakage problems.

Despite appearing solid from the surface, cold joints are inherent weak points in a concrete structure.

SwellCaulk is engineered to permanently seal cold joints. Its expanding action allows it to create a strong bond with both concrete layers, forming a continuous, flexible and active seal.

• Designed to seal cold joints in cast-in-place and precast concrete
• Seals non-bonded gaps caused by pour delays
• Creates a permanent watertight barrier at potential failure points