The present invention relates to a method for suppressing mold formation on building parts using hydrophobic substances, wherein a dispersion of hydrophobic particles having a mean particle diameter of from 0.005 to 5 .mu.m in an organic dispersant is applied to the surface to be protected from mold attack and the dispersant is then removed, and to a composition for building parts which inhibits mold growth and comprises from 0.1 to 10% by weight of hydrophobic particles having a mean particle diameter of from 0.005 to 5 .mu.m dispersed in an organic dispersant.