Optimization of lime and clay-based hemp-concrete wall formulations for a successful lime rendering

Different pathologies may arise on a wall finish if this is applied on a hemp-based rammed wall that is not completely dry. By simulating uneven drying and early-rendering of load-bearing and non-load-bearing hemp concrete blocks (made with natural hydraulic lime only or a mix of lime with clay) and studying them by means of chromatic, microbiological, textural and morphological investigations, we found that: it is advisable to wait at least ten weeks before rendering; adding clay to hemp concrete delays drying, leading to more intense deterioration of the render; natural hydraulic lime is the preferred binder for rendering hemp concrete.