An adhesion bond strength enhancer for cementitious adhesive mortar is disclosed. The adhesion enhancer improves bond strength between the mortar and relatively hydrophobic plastic material, such as extruded polystyrene boards and expanded polystyrene boards of the type generally employed in Exterior Insulation Finishing Systems (“EIFS”). Preparation of non-caking, free-flowing, solid dialkyl sulfosuccinate compositions for use as the adhesion enhancer is also disclosed. The adhesion enhancer is attractive for large-scale application in mineral mortar dry-mixes or other solid construction materials. The invention can be used to improve the strength of an adhesive bond between a) gypsum based plaster or stucco and concrete or bricks, b) tile adhesives and concrete, and c) mineral mortars on polystyrene boards, among others.