A method of preparing an antimicrobial coating comprises coating a surface with an aqueous mixture of 3-(trihydroxysilyl)propyl dimethyloctadecyl ammonium chloride, 3-chloropropyltrimethoxysilane, and triethanolamine and then coating the surface with an aqueous titanyl sol-gel solution comprising an aqueous mixture of peroxotitanium acid and peroxo-modified anatase sol overtop of the silane to form the antimicrobial coating. The antimicrobial coating exhibits residual antimicrobial efficacy against E. coli and S. epidermidis after water rinsing or after abrasion. The use of 3-chloropropyltrimethoxysilane was found to improve storage stability of the quaternary silane composition and the durability of the antimicrobial coating.