I have been placing quite a few concrete floors that are scored in 32-inch squares. The finish on these floors is hand troweled. When completely cured, the floor is either acid stained and waxed or simply waxed. I usually use a black wax. My problem is this: I am getting larger size work to finish in this manner and the number of finishers required is prohibitive. The only source of so many skilled finishers is an union crew. I find that they stand for about 4 hours until the floor is ready to finish, and then they end up working long hours of overtime. Additionally, in hot weather, a large slab will "get away" from even the most faithful crew under these finishing requirements. I am considering several alternate methods of doing the finish: 1. Use a retarder in some of the finish to control it until finishers can get to it. 2. Place separate monolithic castings by dividing the building into sections where feasible. 3. Use a pea gravel topping of about 1 3/4 inches to provide better control of the finish. 4. Use a thin topping--about 1/2 inch thick--of a better grade grout. It is difficult for me to evaluate the various aspects of these alternatives. But, for the following reasons, number 4 appeals to me most: 1. The work can be stopped at any point. 2. This method permits construction to proceed beyond the finish floor work. 3. The method uses small amounts of material which can be prepared in small batches. 4. The method is most flexible in manpower requirements. Crazing is a desirable feature on these floors because it enhances the antique quality of the squares. Can this be obtained with the proper mix? I am aware that there are several ways to get thin, long-wearing toppings, but I do not know how to go about evaluating these other techniques. I would appreciate any comments you might have about this problem.
You are producing a highly satisfactory floor, but the delay in finishing makes it a rather expensive floor. The 4-hour waiting period seems excessively long. It could be shortened by using a rich mix (6 1/2 to 7 bags cement per cubic yard of concrete) of not more than a 2-inch slump. The use of high-early-strength portland cement (Type III) would also reduce the waiting time by at least 1 hour. If the area is large, place the concrete in separate or alternate sections. A separate floor topping is a possible approach to your problem, but it would involve a special preparation of the base concrete and grouting before the topping is applied. A 5/8-inch topping is possible, but this work requires expert craftsmen, a 1:1:2 mix (by weight) using coarse aggregate between 3/16 and 3/8 inch, and practically a no-slump concrete. This no-slump concrete must be compacted to bond well to the pre-wetted base and must be preceded by the application of a 1:1 cement-sand grout. A 3/4-inch to 1-inch topping would be somewhat easier to apply. In order to have the job well under control, you should mix the topping concrete on the job, weighing out fine and coarse aggregate. You are right that this topping can be applied at any time, either integrally or when the base concrete is several days old. The monolithic slab could be economical if you made the suggested modification in mix design and slump. Try that first before going to a separate topping. In regard to admixtures, manufacturers of accelerators and retarders should be ready with technical advice.