Improvement of Local Gypsum Plaster Setting Time by the Combined Usage of (TGP) and (PVA) Additives

An investigational study had been done in this research to improve the setting time of Local Gypsum Plaster by using two additives, namely : Tree Glue Powder (TGP) and Polyvinyl Acetate (PVA). For this objective four sample mixtures had been made, the first sample is the reference sample (mixture without additives), the second and the third mixtures are made by adding one of the two additives; Tree Glue Powder (TGP) and Polyvinyl Acetate (PVA) respectively, while the fourth mixture is prepared by the addition of both additives (TGP and PVA) together. Because of the importance of "the Compressive Strength" property in gypsum works, it was taken into consideration together with the "Setting Time" property in the assessment of results in this study. It was found that, when adding (TGP) alone with a content of (1.0 %), the setting time of the mixture was extremely increased by (333.8 %) as compared with that of the reference mixture, while the compressive strength is reduced by (18.8 %). And when the other additive (PVA) with a content of (4%) was added to the (TGP) mixture (altogether), an almost similar increase in the setting time has occurred (equals 306 %), with an attendant slight improvement in the compressive strength (equals 2.2 %).