Résumé
Conserving of weathered limestone historical structures is an important target for many interested Egyptian builders. Studying the original mortar of any limestone archeological building led to thinking about a new suitable mix design of mortar. The chemical composition of the old studied mortar shows enrichment in chlorides, ammonia and sulfates. Seven mixes composed of different quotients of sand, lime and gypsum were prepared for choosing the suitable one as restoring mortar. X-ray diffractograms of the suggested mortar mixes show composition of quartz, gypsum and calcium hydroxide as the main minerals comprising all mixes. Calcium silicate hydrate [C SH] and di- calcium silicate hydrate [CSH] phases were detected with mixes, which contain considerable gypsum and sand. Mix No.1 [60% sand, 30% lime and 10% gypsum] is considered to be the best blend for mortar. Such mix achieved reasonable compressive strength, bulk density and water absorption values along all of the studied curing times. This work suggests that the using of sand, lime and gypsum mortars is adequate for repairing and conserving the historical and archeological limestone buildings