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Aims: Studying the effect of microwave drying on the physical and mechanical properties of modifiedIraqi plaster and modified Plaster of Paris in comparison with open air drying method. Materials andmethods: Two types of gypsum products were used in this study (Iraqi plaster, Plaster of Paris) withthe combined additives (gum arabic 0.5%, calcium oxide 0.75%, and ferric oxide 0.2%) that incorporatedwithin the two gypsum products. Physical and mechanical properties of the experimental gypsumproducts have been evaluated by measuring the compressive strength, surface hardness, and surfaceroughness. Mean, standard deviation, analysis of variance (ANOVA), and Duncan's multiple rangestatistical test were used to analyze the data. Results: ANOVA analysis showed that there was a significantdifference in the compressive strength, surface hardness, and surface roughness between Iraqiplaster (I.P) and Plaster of Paris (P.O.P) with or without additives. Conclusions: At two hours timeinterval microwave oven drying, Iraqi plaster and Plaster of Paris samples were stronger than air driedsamples; and microwave oven at 10 minutes for 800 Watt not only increased the strength of gypsumproducts samples, but also save time.

Aims: A pilot study was done to evaluate the physical and mechanical properties of the Iraqi plaster (Al- Ahliya gypsum) and Plaster of Paris (British Gypsum), and to improve the quality by the incorporation of some additives. Materials and Methods: Two types of gypsum products were used in this study (Iraqi plaster, Plaster of Paris). Three types of additives {gum arabic at a concentration of (0.1%, 0.25%, 0.35%, 0.50%), calcium oxide at a concentration of (0.1%, 0.25%, 0.35%, 0.50%, 0.75%), and ferric oxide acts as a pigment (blue or red) at a concentration of (0.1%, 0.2%)} were incorporated after preparation into the weighted dried gypsum powder. The effects of these additives on the physical and mechanical properties of the experimental gypsum products (Iraqi plaster and Plaster of Paris) have been evaluated by measuring the water/powder ratio, setting time, linear setting expansion, and compressive strength. Four hundred sixty gypsum samples were prepared for this study. Mean, standard deviation, variance (ANOVA), and Duncan's multiple range tests were used to analyze the measurements. Results: ANOVA showed that there was a significant difference in the water/ powder ratio, setting time, linear setting expansion, and compressive strength between Iraqi plaster and Plaster of Paris depending upon the type and the concentration of each additive used. Conclusions: The last concentration of each additive (gum arabic 0.5%, calcium oxide 0.75%, or ferric oxide 0.2%) in all the experimental measurements that are incorporated within the two gypsum products showed