Cinders should be composed of hard, clean, vitreous clinkers, free from
sulphides, soot, and unburned coal or ashes. As a precaution against the
presence of small amounts of detrimental substances, cinders should be
soaked thoroughly with water 24 hours before being used. If clean they
will not discolor the hands when a small quantity is rubbed between the
palms.
Cinder concrete, on account of its light weight, commonly is used for
filling between sleepers of floors and grading roofs, and frequently for
fireproofing, for which it is very effective. Cinders should never be
used when the concrete is to be subjected to heavy loads or abrasion.