Natural additives and biopolymers for raw earth construction stabilization – a review

•Natural stabilizer’s efficiency is related to the earth's composition.•The use of experimental framework and guidelines is advised for results comparison.•Biopolymers binds modify ductility, plasticity, viscosity, hydrophobicity and cohesion.•Need of a systematic frame to conduct studies and report material data is emphasized.•Microscopic interactions between clay and biopolymers require further investigations. The importance of earthen construction materials lies in their widespread availability combined with a low embodied energy. Chemical stabilizers are commonly used to improve their durability and mechanical performance. The main drawbacks are the high environmental impact of their production, the loss of recyclability, and the possible reduction of raw earth’s hygrothermal properties. Historically stabilization was achieved by the use of different kinds of fibers, agricultural wastes, and biopolymers incorporated into the earthen matrix. The purpose of the present study is to review the state of the art of investigations on the influence of natural additives for raw earthen materials, to promote and facilitate future research in this field. More than 50 independent studies have been considered, including different types of raw earth constructions: plasters, adobe, compressed earth blocks and rammed earth. To enlarge the opportunity of investigating the use of biopolymers as stabilizers, some studies about soil stabilization have been included in the review. Results show that the use of recycled and waste material as a natural additive is promising direction for future research as it can provide a sustainable alternative to chemical stabilization.