Improving the durability of straw-reinforced clay plaster cladding for earthen buildings

Many historic earthen structures in the Middle East, Central Asia, and parts of Africa and Latin America are traditionally protected against the rain by straw-reinforced clay-plaster applied as a protective layer to the exterior of the building. The plaster is effective in keeping the building dry and can sustain the severe temperature changes of the regions; however, the plaster is susceptible to relatively fast water erosion. This article presents the results of a program of experiments, aimed at enhancing the durability of this traditional plaster against rain erosion. Hydrated lime and a very fine-grained aggregate (crusher dust) are used to improve the resistance of the straw-reinforced plaster. Samples made of the improved plaster mixes are tested for compressive and flexural strengths, water tightness, and resistance to water erosion; the results are used to obtain an optimum mix proportion for the improved clay soil plaster. The results indicate a substantial increase in the strength and durability of the plaster by using small quantities of these low-cost additives.