Abstract: A cementitious building product such as a siding clapboard is composed of about 30 to 50% cement, 40 to 60% sand and 5 to 15% fiber, by volume. A preferred mix has about 35% portland cement, 55% fine sand and 10% cellulose fiber by volume. As so composed the product can be worked after curing in a manner similar to wood. At least one elongated cut is formed after curing the product in the shape of an elongated board or plank, preferably by planing or routing the product along an edge to form a distinct bead that can be round, teardrop shaped, crowned or coved.