Cement mortar contains calcium carbonate and calcium sulfate. If not properly maintained, the free calcium or free magnesium separates from the plastered wall in high temperatures and humidity. It forms efflorescence, commonly known as wall mold. This study used six experimental groups with brick wall cement blocks coated with moisture-proof coatings and two control groups. The temperature and humidity sensors were embedded in the test samples to monitor deep layers’ temperature and moisture content for a long time. An air temperature and humidity recorder was placed on the inner side of the wall. An outdoor weather station was placed on the outer side to monitor the outdoor temperature and humidity. A gun-type infrared thermometer was used to measure the surface temperature of eight outside (outdoor) and inside (indoor) groups. This study found the preferred moisture-proof coating and discusses the selection of moisture-proof coating for the cement mortar plastering layer. Based on the results, suggestions are presented for water resistance and moisture permeability of innovative composite moisture-proof materials in the future.