Q.: We are under contract to build a large custom home. The buyers want to have concrete floors kept uncovered and with a shiny finish. We have never done this before and are seeking information for varnishing the slab.
A.: You should first be sure you produce a good, smooth, hard troweled finish. You will also want to take precautions against cracking by using good jointing procedures. An adequate amount of welded wire fabric used in the slab will limit crack width in case shrinkage-temperature cracks do occur. The fabric should be positioned about 2 inches below the surface. You can find good instruction on both finishing and jointing in ACI 302, "Guide for Concrete Floor and Slab Construction," available from the American Concrete Institute, Box 19150, Detroit, Michigan 48219. A good publication on the use of welded wire fabric is Using Welded Wire Fabric in Residential and Light Construction, available without charge from Wire Reinforcement Institute, 7900 Westpark Drive, McLean, Virginia 22102.
The coating should be an epoxy or a polyurethane coating, either of which will provide excellent wear resistance, though you should understand that not all epoxies have the same wear resistance, nor do all polyurethanes have the same wear resistance. You will have to ask the manufacturers which of their products are epoxies or polyurethanes and suitable for use as floor coatings.
Another possibility is to produce a maximum amount of shine by a sufficient number of hard trowelings, and then improve the shine by applying a slip-resistant wax.