Waterproofing Chemicals

Polymer-modified bitumen (SBS or APP) in sheet or liquid form is the most widely used for roofing and underground structures. Polyurethane (PU) liquid-applied membranes (1K moisture-cure or 2K) are used for complex geometries (rooftop gardens, balconies, tunnels). Cementitious crystalline systems (CCCW) penetrate into concrete and self-seal cracks. Acrylic and SBR-based elastomeric coatings are used for below-grade dampproofing.

SBS (styrene-butadiene-styrene) is a thermoplastic elastomer added to bitumen to improve cold flexibility and elastic recovery — SBS-modified bitumen remains flexible at -25°C and is preferred for cold climates. APP (atactic polypropylene) improves heat resistance (softening point > 120°C) and oxidative stability — preferred for hot climate torch-applied membranes and flat roofs with high solar load.

PMMA (polymethyl methacrylate) reactive liquid membranes cure in 20–45 minutes regardless of temperature (even at -10°C), allowing rapid return to service. They have excellent UV stability, bond well to wet concrete, and can be applied in cold or damp conditions. PMMA has higher raw material cost than PU but is preferred for bridge decks and car park decks where rapid reopening is critical.

Root-resistant membranes are tested per EN 13948 (4-year resistance to common roof-garden plants) or the FLL standard. SBS-modified bitumen with FLL-tested formulations and root-resistant PVC membranes are common. A copper-foil root-deterrent layer is sometimes added. The drainage layer above the membrane prevents pooled water and protects the membrane mechanically against root penetration over the design life.

Pre-applied (loose-laid) membranes are placed before concrete pour — they bond to fresh concrete during curing, eliminating water tracking between membrane and concrete. Post-applied membranes (paint-on or sheet) are applied after concrete cures — useful for retrofit but require dry, clean substrate. Pre-applied HDPE-based technology with adhesive layer is increasingly specified for new tunnels and basements.

Below-ground waterproofing is specified by water-table conditions: above water table uses dampproofing (asphalt or solvent-based bitumen); below water table uses positive-side membrane (HDPE, EPDM, or thick SBS-modified bitumen) at hydrostatic-rated thickness. Type A (barrier), Type B (structurally integral, e.g., crystalline concrete admixture), and Type C (cavity drainage) classifications guide selection per BS 8102 or equivalent standards.