Summary and Conclusions

This study investigated the effect of moisture content, drying time, drying conditions, and clay content on the strength and elastic modulus of an earthen plaster. The plaster was mixed using soil consisting of 69% silt, 27% clay and 4% sand. The earthen plasters were also compared to a plaster mixed using a commercially available clay, and cement-lime plasters. The specific conclusions of this work are:

(1) The stress-strain response of the earthen plaster was similar to that of concrete or cement-lime plaster.

(2) The initial moisture content of the earthen plaster had a negligible effect on the strength and elastic modulus. This is in contrast to structural concrete or cement-lime plasters.

(3) There is a negligible increase in compressive strength, but a significant increase in elastic modulus with 10 to 18 days of drying of an earthen plaster.

(4) Increased clay content significantly increased the strength of the earthen plaster.

(5) Placing the plaster in a 110°C oven substantially reduced the moisture content and increased the strength. Leaving the plaster in a humid environment increased the moisture content and resulted in lower strength as opposed to a lab environment.

(6) The earthen plaster had higher strength and elastic modulus than typical cement-lime plasters used for straw-bale construction. The earthen plaster also had higher strength and elastic mod­ulus than the plaster mixed with commercial clay.