We are preparing construction documents for remodeling a junior high school shower and locker room. The building was constructed in the thirties. Floor construction is a four-inch thick concrete slab on grade with a 1 l/2-inch concrete topping. The topping has cracked badly but it is still bonded to the base slab. The School District wants to seal the floor to eliminate a potential health hazard and, if possible, to create a more eye-appealing floor. What do you recommend?
There are a number of methods available for repair of such a floor. We would like to suggest three: use of thin-bonded concrete resurfacing, terrazzo, or epoxy resins. Thin-bonded resurfacing. The existing badly cracked 1 1/2-inch topping should be removed by jackhammering; otherwise, reflection cracks would be likely to develop in any new topping bonded directly to the old topping. The base is then acid-etched, flushed clean with water and kept wet overnight. Before placing the topping mix, a slush coat of portland cement and water is broomed into the surface. Details of this procedure are given in the reprint collection on "Repair, available from CONCRETE CONSTRUCTION. Terrazzo finish. Terrazzo finishes can be installed over practically any type of existing floor finish. For example, an attractive bonded portland cement terrazzo surface may be applied. In this method the old topping is removed and the base slab prepared for bonding as above, including the use of the portland cement slush coat. A bed of portland cement and sand mortar is then placed and struck off one-half inch below the final floor level desired. While this mortar bed is still semiplastic terrazzo divider strips are installed. Next the terrazzo topping mix is prepared using the desired type and color of marble chip with white or gray portland cement and possibly a color pigment. Again a slush coat of cement and water is applied and the terrazzo is placed and finished level with the top of the strips. Finally the topping is finished by grinding. More details of this method are given in the reprint collection on "Concrete Floors" available from CONCRETE CONSTRUCTION. Only a qualified terrazzo contractor should attempt this repair. If the existing architectural conditions limit the finish thickness, perhaps one of the thin set terrazzo toppings chemically bonded to the existing topping would be the best solution. The relative thinness of these toppings (one-fourth to one-half inch in thickness) is possible because the resinous binders such as epoxy used in them have high bond strength. Such a surface can be attractive and impermeable and it would minimize development of reflection cracks. Further information on thin set terrazzo toppings is given in the same reprint collection on "Concrete Floors. " Epoxy resin coatings. Still another possibility would be to squeegee a low viscosity epoxy over the surface of the existing slab and into the cracks. The final finish over this surface could be a paints probably another epoxy with or without a fine aggregate broadcast to make the surface more attractive and slip resistant. Materials formulated especially for this purpose should be used.