This invention provides facing materials for cementitious boards such as those
including Portland cement or gypsum cores. The preferred facing material includes,
in a first embodiment, a facing layer having an areal weight of about 300 grams/M2,
and an air permeability rating of no greater than about 300 CFM/ft2 (FG
436-910 test method). The facing layer reduces the penetration of a slurry of cementitious
material during the manufacture of a cementitious board, while permitting the water
vapor from the slurry to pass therethrough. The facing materials of this invention
can be designed to substantially eliminate the fouling of rolls used in continuous
processing of such boards without the use, or with greatly reduced use, of costly
viscosity control agents in the slurry. In addition, further embodiments of this
invention can include binders, coatings or saturants which are designed to decrease
pore size, increase or decrease the contact angle of liquids, or promote greater
adhesion to cementitious cores, greater adhesion to other layers in the facing
material, or greater adhesion or affinity to various types of adhesive compositions
used to join cementitious boards to insulation and exterior finishing systems (EIS
or EIFS).