The Ontario Building Code | Topping Course
220.127.116.11. Topping Course
(1) Where a topping course is provided for a concrete floor slab, it shall consist of 1 part cement to 2.5 parts clean, well graded sand by volume, with a water/cement ratio approximately equal to that of the base slab.
(2) When concrete topping is provided it shall not be less than 20 mm thick.