Masonry Magazine February 1993 Page. 58
inches, and not less than one times the footing projection unless reinforced. Example: For a 15" x 20" masonry unit excavate a hole approximately 4' x 5' x 4' deep. If a form were constructed to the dimensions 24" x 32" the footing projection would be 6" and the thickness would be 9". (Refer to detail A).
Allow the concrete to cure for at least 24 hours before beginning construction of the chimney.
Base Section
A cleanout opening must be provided in all chimney flues. The cleanout must be equipped with a non-combustible door and frame which will remain tightly closed when not in use.
Begin the masonry units at the top of the footer and place the cleanout in the first two units completely above ground. Fill in the first four and one half masonry units with a prepared gravel mix concrete to bring the solid base closer to ground level, or fill the first four units with compacted gravel and place a 4" solid concrete base on which to begin the flues. Prepare a bed of refractory cement on top of the concrete to receive the first section of the flue liner. This will create the proper base and keep the flue liner in place. Mortar for flue linings must be a refractory cement. (Refer to detail A).
Flue Liners
Every chimney designed to service a wood burning stove must have a fire clay flue lining with a minimum thickness of 8 in. The flue lining should provide continuous protection of the surrounding masonry throughout the chimney. Flue liners should begin at the base of the chimney and must be offset so that their joints do not occur at the same place as the joints between the masonry units. Flue linings should be capable of
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58 MASONRY-JANUARY/FEBRUARY, 1993