Gypsum‐Based Self‐Leveling Mortars Modified With an Emulsified Waterproofing Agent: Physical and Mechanical Properties and Microstructure

ABSTRACT Hydrogen‐containing silicone oil (HCSO) is widely used as a waterproofing agent in building materials, yet its tendency to agglomerate leads to uneven distribution and poor performance. In this study, we developed a controllable emulsification strategy—using Span 80, Tween 80, and OP‐10 at a mass ratio of 8:1.6:6.4 (HLB = 9.05)—to produce a stable emulsified HCSO (EHCSO) with a stability value of 1. By incorporating 0.8 wt% EHCSO into gypsum‐based self‐leveling mortars (GSLMs), we achieved an optimal balance of properties: apparent density of 1.26 × 10 3 kg/m 3 , softening coefficient of 0.85, flexural strength of 6.81 MPa, compressive strength of 20.90 MPa, and contact angle of 126.39°. X‐ray diffraction and SEM analyses confirmed that EHCSO does not alter the hydration phases but promotes the in situ formation of short columnar dihydrate crystals that fill pore spaces, refining the microstructure and enhancing mechanical integrity. This work contributes to the field by (1) introducing a scalable surfactant formulation for uniform HCSO dispersion in gypsum systems; (2) quantifying the link between surfactant HLB, emulsion stability, and waterproofing performance; and (3) demonstrating a dual improvement in both durability and strength, with potential applicability to a broad range of cementitious materials.