Mason productivity is determined by architectural design, contractor efficiency, mason skill, and weather. Thermal stress in humans is affected by the balance between metabolism and evaporation, convection, and radiation. These heat transfers are affected by environmental conditions of temperature, humidity, air movement, and radiation. Correlations between all thermal stress variables and labor productivity have not been established for construction craftsmen. However, relationships between mason productivity and temperature and humidity have been established. Meteorological data from 73 United States weather stations have been used to determine geographical variations in mason productivity as affected by these climatic variables.