A synergistic antimicrobial composition containing chlorotoluron and 3-Iodo-2-propynyl butylcarbamate is provided. Also provided is a method of inhibiting the growth of or controlling the growth of microorganisms in a building material by adding such a synergistic antimicrobial composition. Also provided is a coating composition containing such a synergistic antimicrobial composition, and a dry film made from such a coating composition.
