To follow expandability of a substrate by applying urethane resin as finish coating via a primer and undercoating after grinding of a concrete substrate.

After the surface of placed concrete is smoothed being sanded with a polisher, polished material is sucked and eliminated by a cleaner for surface treatment. An epoxy resin solvent is applied as a primer with a roller brush, and epoxy resin is applied as an undercoat with a trowel. After undercoating is executed, urethane resin with zeolite added as an adsorbent is applied as coating material to the surface of the undercoat by troweling work to finish a coated floor. The adsorbent is mixed to avoid a foaming phenomenon under high temperature and high humidity, and diatom earth, activated charcoal or activated clay can be used instead of zeolite. Substrate expansion is therefore followed well to prevent the formation of a crack.