When sealing cracks in slabs or foundation walls, which type of caulk is required?

When sealing cracks in slabs or foundation walls, the recommended type of caulk is urethane or polyurethane that complies with ASTM C920 class 25. This specific requirement is crucial because ASTM C920 sets the standard for the performance and durability of sealants used in construction, particularly in scenarios where movement is a factor, such as in concrete slabs and foundation walls.

The “class 25” designation indicates that the sealant can accommodate up to 25% movement in extension or compression, which is essential for maintaining a watertight seal in areas that experience dynamic pressures or shifting due to settling or thermal expansion and contraction. Urethane and polyurethane caulks are known for their excellent adhesion, flexibility, and resistance to moisture, which makes them especially suitable for outdoor applications and areas that frequently encounter environmental stressors.

This specific formulation provides not only the necessary flexibility to withstand movement but also ensures long-lasting durability, helping to prevent further damage to the foundation or walls from water intrusion, ground movement, or thermal effects. Thus, selecting this type of caulk for sealing cracks is critical for effective radon mitigation and structural integrity.