Masonry components of Historic building in Bagamoyo, Tanzania have suffered considerable deterioration in a variety of forms, and close examination indicates that the root cause of the deterioration of the structure is mainly due to masonry mortar joint failure because of chemical and physical degradation of the material. This paper examines the colours, physical and mechanical properties as well as chemical composition of the mortar; thus its replacement carefully matches the historic in chemical composition, strength and texture as determined by a laboratory analysis. In terms of colour, the mortars were divided into three groups of colours namely light grey, light brown and light yellowish brown. Point counting by microscopical study indicated that the hard mortar has higher binder content and composed of a homogenous hydraulic matrix and a heterogeneous coarse fraction with moderate voids while the moderate hard mortar contained modest binder and soft and friable lime mortar contained little hydraulic binder. The results of chemical composition indicated that the stones composed of high amount of Calcium Oxide (CaO) while the mortar contained low percentage of CaO indicating that the mortar is not pure hydraulic lime but hydrated lime (air-hardening lime).
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