The present disclosure is generally directed to a mold inhibiting composition. The mold inhibiting composition can be used to treat various different substrates, including building material products, such as facing layers for wallboard. In general, any suitable paper product may be treated with the composition. The composition contains a mold inhibiting agent in combination with a defoamer. The mold inhibiting agent may comprise a pyrithione. The defoamer, on the other hand, may comprise an oil based defoamer containing metal oxide particles, such as silica particles. The mold inhibiting composition can be combined with a water repellent and applied to a substrate without excessive amounts of foam or froth being formed. The defoamer is selected so as to not interfere with the resulting water absorption properties of the product.