The formation of efflorescence required 3 conditions: 1. Sufficient free calcium, 2. Sufficient humidity, 3, proper temperature change. Cement is abundant in calcium, if the cement mortar on the wall is in damp environment, the free calcium is easily soluble in moisture, once in cold and dry climate, the calcium-containing moisture will permeate onto the surface, when the moisture is evaporated, the calcium will be subject to dehydration and crystallization to form efflorescence, the climate in Taiwan is quite suitable for the formation of efflorescence, there¡¦s no effective prevention of efflorescence except water prevention at present, efflorescence shrivels plasterers, ¡§the cancer on the wall¡¨ has become a nightmare of many people.