A thin, distinct layer of contrasting rock, usually clay or shale, that separates massive beds of limestone or sandstone. Wayboards act as planes of weakness in the rock mass, making them critical features for ground control because they allow massive roof blocks to detach and fall if not properly supported.
Heard on the job
The roof bolt needs to anchor at least two feet past that clay wayboard to hold the lower limestone block.
Insider tip
Wayboards often form natural boundaries for underground excavations, allowing miners to break the rock cleanly along the flat clay seam.