The present invention concerns an antimicrobial composition, a process for making antimicrobial building construction surfaces, and building construction products treated with the composition on their surfaces. The water based antimicrobial composition disclosed comprises a water resistant polymer, at least three organic based antimicrobial agents, with at least one antimicrobial agent being halogen containing, and at least one antimicrobial agent being non-halogen containing. The composition is useful for treating the surfaces of building construction materials to make products that are highly resistant to microbial growth even in severe environments.