Cementitious vs Polyurethane Waterproofing: When to Use Each

Cementitious waterproofing and liquid-applied polyurethane (PU) membranes are both widely used on internal wet areas, planters, podiums, and roofs. They behave very differently in service, and the wrong choice on a substrate with movement will lead to early cracking and leaks.

How each system works

Cementitious systems are powder-and-liquid blends — typically a polymer-modified cement matrix — that cure into a rigid, mineral-bonded coating. They bond chemically to concrete and are vapour permeable, allowing the substrate to breathe. Liquid PU membranes are single- or two-component polyurethane that cure into an elastomeric film with significant elongation. They form a continuous, flexible membrane that bridges hairline cracks.

Side-by-side comparison

Decision framework

• Static substrate with potential hydrostatic pressure → cementitious.
• Exposed substrate with thermal movement → liquid PU (or polyurea).
• Potable water tank → certified cementitious system.
• Planter or podium with overburden → liquid PU under protection board.
• Below-grade with risk of water ingress from outside → negative-side cementitious.