Multifunctional primer formulations are disclosed for composite building materials, such as materials that are generally cementitious, gypsum, or of another inorganic building material, including those containing cellulose, glass, steel or polymeric fibers. The multifunctional primer formulations provide multifunctional action to the primer including an ability to function as a primer and sealer in only a single coating. Such formulations when applied to a suitable substrate provide excellent adhesion to the substrate and improve paint adhesion and performance when applied thereto. Superior properties over commercial products is particularly notable when the formulations herein are applied to substrates, such as fiber cement, that have been manipulated or sized by cutting (e.g., by saw or water jet), sanding, punching, and/or shearing.