A vibrating smoothing device or plate transverse to a direction of travel of deposited gypsum-cementitious slurry and embedded chopped fibers. The plate is used to smooth the top surface of the slurry panel as it exits a first fiber embedment station and a second slurry depositing station before passing through a second fiber embedment station of a structural cementitious panel production line to remove grooves and other non-uniform surface imperfections to have the slurry cover the embedded fibers The plate is designed to float over the surface of the formed slurry without tearing or otherwise damaging the surface of the heavily fiber reinforced surface layers of the formed slurry before it sets. The vibrating plate is pivotally mounted on the web production line so it can float over the panel surface during use, but be raised off the line when not in use.