Epoxy coatings can be used as: (1) an epoxy mortar provided they contain no solvents; (2) a film with broadcast aggregate for skid resistance; and (3) a clear film in areas where there is no traffic. As a mortar, it is spread evenly to smooth out any unevenness. It is then troweled to a smooth, hard finish. When properly cured this finish will provide not only resistance to heavy traffic but in addition the finish will provide extremely high resistance to chemicals, oils and other materials. The epoxies can also be used as a film with skid resistant aggregate. While the coating is still wet, an excess of selected fine aggregate such as sand should be broadcast over the film. After the film has cured, the surplus aggregate is brushed off. The epoxy system surface coatings have one big advantage: they will penetrate and seal small cracks. The cracks should be filled by pouring the coating into them some time before the overall surface coating is applied. In this way the epoxy material will be able to penetrate to the maximum depth and glue the crack together, filing it up to the top and then leveling off with the surface coating later. It should be noted that epoxy systems should generally not be used over slabs-on-grade, particularly in northern United States, where the slab will be subjected to freezing and thawing over long periods of time. In summer months when the slab is exposed to the sun, water vapor will rise from the subsoil and pass through the concrete as vapor. However, upon reaching the epoxy coating this water vapor will condense into water. The water cannot go back through the concrete, so it lies between the slab and the coating. In winter, the water freezes, spalling the concrete.