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This research presents a study of using an additive for the objective of increasing the setting time of a material used in several aspects in the constructional field, this material is “Local-Gypsum” which is locally called “Joss”, and the additive used in this study is “Trees Glue Powder” denoted by “TGP”. Nine mixtures of Local-gypsum (joss) had been experimented in the current study to find their setting time, these mixes were divided into three groups according to their water-joss ratios (W/J) (0.3, 0.4 and 0.5), and each group was sub-divided into three sub-groups according to their TGP contents (0.0%, 0.3% and 0.6%). It was found that, when TGP is added with the two contents (0.3% and 0.6%), the setting time of local gypsum (joss) is increased, and the percentage of this increase at (TGP content = 0.6%) is doubly multiplied as compared to the percentage at (TGP content = 0.3%). Moreover, when TGP content is increased from (0.0% to 0.6%), the percentage of increase in the setting times of joss is reduced with the increase of (W/J) ratio from (0.3 to 0.5). It was also found that, when (W/J) ratio is increased, the setting time of joss is increased, and this behavior is applicable for all TGP contents (0.0%, 0.3% and 0.6%). While, when (W/J) is increased from (0.3 to 0.5), the percentage of increase in the setting times of joss is reduced with the increase in TGP contents from (0.0% to 0.6%).

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The current work studies the effect of adding chopped carbon fiber (CCF) on gypsum plaster properties (precisely the compressive strength and the modulus of rupture). The research plan consists of using six mixes of gypsum plaster; these mixes are divided into two groups according to the (Water/Gypsum) ratios (0.5 & 0.6). Each group was divided into three subgroups according to CCF volume fraction (Vf): 0.0%, 0.2% and 0.4%. Three cubic (50×50×50) mm and three prismatic (40×40×160) mm samples were performed for each mix. It was found that, the addition of CCF to the gypsum plaster mixes increases both the compressive strength and the modulus of rupture for both (W/G) ratios, and the percentage of this increase is enlarged with increasing (W/G) ratio. On the other hand, when (W/G) ratio is enlarged, the compressive strength and the modulus of rupture is deteriorated for all (Vf) of CCF, and this percentage of deterioration is decreased in the presence of CCF.