Introduction: The use of earthen materials is common in hot and dry areas around the world, due to a cheap, abundant and easy access to materials. Today, the use of earthen materials is common in urban and rural areas in developing countries. In Iran earthen materials have partly shaped our architectural culture and identity. Kahgel is one of the oldest traditional plastering and mortars in Iran, which has been used to insulate the roof and facades of buildings from moisture and rainfall. Although the importance of processing and curing mortars and plasters is well known among architecture and building professionals and builders, no research has been conducted on the effect of processing time upon the physical quality and mechanical properties of traditional mortars, especially Kahgel. The main purpose of this study is to evaluate the importance and duration of curing process on the physical and mechanical properties of Kahgel using experimental methods.

Material and methods: As the first step, soil samples were taken from different areas of Isfahan and then these samples were examined using different experimental methods. Then the most appropriate soil sample in terms of physical and mechanical properties was selected. Several samples of Kahgel mortars were produced using the selected soil sample and different percentages of straw fibers. For these kahgel samples the compressive strength, tensile strength, linear shrinkage and cracking were measured to determine the most appropriate combination of selected soil mixed with straw fibers. In the second phase of the study, the type of soil and straw percentage were not changed, while the processing time was considered as an independent variable. The new Kahgel samples were prepared by a variety of processing time and then their compressive strength and tensile strength were measured to examine the effect of the curing time on the mechanical properties of Kahgel.

Results: The results indicate that the compressive strength dropped with increasing straw fiber content and increased with increasing soil content. The results of all the tests indicate that tensile strength of Kahgel increased with increasing straw fiber content up to 6 %, but the higher straw contents decreased tensile strength. The linear shrinkage of samples decreased with increasing straw fiber content. The results showed that the curing time of Kahgel affects its mechanical properties, especially compressive strength and tensile strength. Therefore, the mechanical properties of Kahgel can be improved by increasing the duration of curing time.