A synergistic antimicrobial composition containing a glyphosate compound 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. Also provided is a method of making zinc glyphosate.
