The vacuum tube in a CRT can implode if it is broken or punctured. The surrounding air will rush violently into the unsealed vacuum in the CRT, spraying broken glass in every direction. Color CRTs may contain mercury or other potentially toxic materials.
Instructions. Build a hearth for a fireplace that is 16 inches deep, according to This Old House writer Harry Sawyers. This is the standard requirement for municipalities and homeowner associations. The hearth should also extend a minimum of eight inches on either side of the fireplace.
To build a new wooden hearth, measure the area desired next to the fireplace and cut a wood frame using plywood. Cut 2x4 wood pieces and attach to the underside of the plywood with wood glue and nail gun around all edges. Place the hearth against the stone and lay the slate the hearth frame with mortar.