A gypsum wallboard suitable for Level 4 finishing having a coated non-woven first glass fiber mat facing material on one major surface and an optionally coated second glass fiber mat where on the other major surface. The apparatus further includes a sensor for measuring the relative distance between the housing and ground engaging member, and apparatus for selectively stopping the motor upon the distance between the ground engaging member and the housing exceeding a predetermined distance. The acceptor layer has an acceptor layer valence band and an acceptor layer conduction band. The digital controlling device can be digital mirror devices, for example. Each fence has a determined electrical resistance which is used to monitor the validity of the fence.