I am interested in obtaining any information available concerning 1-inch and 2-inch toppings on structural concrete slabs.
This subject is covered in the ACI 302 Standard, "Recommended Practice for Concrete Floor and Slab Construction," Sections 1.3, 7.6, 7.6.1, and 7.6.2. Much of the other information in this same recommended practice would also be pertinent. The top surface of the structural slab should preferably be roughened by brushing with a coarse wire broom when it has partially set. The slab should be cured at least three days using polyethylene or other sheet membrane but not a liquid membrane curing compound. When the topping is to be applied the sheet should be removed and the slab should be hosed with water to remove whatever dirt has collected. As soon as this water has been removed or has evaporated, a grout of 1 part portland cement and 1 part sand passing the Number 8 sieve should be scrubbed in. This grout, mixed to a cream-like consistency, should be applied in segments just ahead of the fresh concrete that is being placed so that the grout is always fresh and damp until covered. If more than about two hours elapses between the removal of the curing sheet and the placing of the topping, the surface should be prevented from accumulating plaster, paint, oil, grease, dirt or other contamination that would inhibit bond. The slab should be kept wet overnight before placing the topping. Its surface should be thoroughly scrubbed with a brush and clean water and then all water removed. The surface is then grouted and topped as already described. If the time that elapses after curing is more than a week and the floor has been subjected to heavy construction traffic, the surface preparation must be more thorough. It should be scrubbed with water containing a detergent. Sodium metasilicate and resin soap may be used to remove grease. The floor should then be thoroughly rinsed. Commercial hydrochloric acid (about 35 percent hydrogen chloride concentration) should be applied at the rate of approximately one gallon per hundred square feet and broomed over the surface until it stops foaming. Workmen should be well protected with rubber boots, gloves, goggles, and possibly rubber suits and respirators. It is also advisable to protect exposed areas of the skin with grease. The floor should be thoroughly hosed, while water and loosened sand are pushed off the surface with stiff brooms. Before proceeding further the surface should be inspected for laitance or dirty concrete and given additional treatment where necessary. All free water should be removed and the same grout treatment used that has been discussed. When the top course has been spread and screeded it is best to use a disc-type power float. The topping should be troweled twice with a power trowel and at least once by hand to remove trowel marks left by the machine. The topping should be given the best curing possible because the hardness obtained will depend directly on the quality of the curing.