For preventing from exfoliation of cement mortar rendering on structural bodies such as reinforced concrete, progress interval time tied with construction cost is important. For optimizing on the time, moisture movements of cement mortar with two plies consisted of cement, silica sand, water and admixtures were measured. Three levels of the time, namely one, three and seven days, were selected in view of actual situation of construction site. The shorter time and the longer one are not desirable for keeping movements stable because of lack of cement hydration or so much water absorption, and for keeping a sustainability from the view points of economy. As a result, the time three days is clarified to be optimum.

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