Application of bromocresol purple dye for plaster drying time determination

•The plaster with BCP has a purple color in the wet state.•The plaster with BCP has a greenish-yellow color in the dry state.•BCP cost is equivalent to 3.67% of the plaster coating total cost.•A mechanism for determination of the drying time of plaster proposed in thepaper.•BCP alone already works as a sensor for determining drying of the gypsum plaster. This paper verified the efficiency in using the acid-base indicator of bromocresol purple (BCP) dye to determine the moment when gypsum plaster reaches the dry state. For this purpose, the materials used were characterized by X-ray diffraction and by scanning electron microscopy (SEM). We determined the following parameters: workability time, geometric porosity, compressive strength, hardness, and tensile adhesion strength. Two dosages of the indicator, 1.6% and 3.2%, were tested and compared with the reference, and we observed that the addition of the indicator did not change the workability time of the paste. In addition, the values of compressive strength, hardness, and tensile adhesion strength, at the 1.6% dosage, were 6.41 ± 0.59 MPa, 14.19 ± 1.08 N·mm2 and 0.48 ± 0.24 MPa, respectively. At the 3.2% dosage, the values obtained for those properties were 5.55 ± 0.67 MPa, 13.81 ± 0.88 N·mm2 and 0.46 ± 0.23 MPa. Moreover, we verified that the BCP indicator can be used to determine the drying of the gypsum plaster coating, either through the analysis of the color change in the sample surface or by using reflectance spectroscopy.