The improved thermal resistance from the paint mixed with CaSO4 whiskers on different substrates (i.e., concrete pillar, stainless steel foil, and calcium silicate plate) has been investigated. An efficient microwave-assisted method is used to synthesize CaSO4 whiskers from wastewater. Experimental results reveal that the addition of CaSO4 whiskers provides a thermal barrier against the heat transfer. The temperature difference between the painting with and without the CaSO4 whiskers exceeds 13 degrees C, indicating superior thermal-insulating performance. The presence of CaSO4 whiskers is capable of providing a fire barrier against the flame at 900 degrees C. The enhanced performance can be attributed to the fact that the CaSO4 whiskers possess an endothermic nature and a high melting temperature (i.e., 1460 degrees C). Accordingly, the introduction of CaSO4 whiskers facilitated not only the thermal barrier but also fire protection of construction coatings, suitably complementing the thermal management for green architecture or buildings. Since the CaSO4 whiskers were prepared from industrial wastewater, the two-step microwave-assisted method offers a straightforward way to produce green construction materials because of its pollutant reduction, non-toxicity, low cost, and environmental friendliness.