Influenza delle finiture sulle prestazioni moisture buffering di blocchi in calce e fibra di canapa

Hempcrete, made with the woody core of hemp plant and a lime based binder, has an excellent hygroscopic performance, confirmed by a consolidated international literature that highlights the capacity of this bio-composite material to dampen the indoor relative humidity variations (moisture buffering capacity) (Collet, 2015; Rahim 2015). However, it is not possible to use hempcrete for building envelope without a finishing layer, due to aesthetic reasons. This study aims to evaluate how different finishing layers could influence the hygroscopic performance of hempcrete, by assessing the water vapor permeability and the moisture buffering capacity of samples finished by a rendering layer and three types of painting: two latex paints and an acrylic based paint. From experimental tests it was observed that the vapor permeability of hempcrete decreases up to 28,5% when finished by acrylic based paint - characterized by a high water vapor diffusion resistance factor - if compared to the unpainted sample. Experimental determination of moisture buffering values (MBV) in accordance with the Nordtest protocol demonstrates that the rendered hempcrete can reach a MBV value of 2,34 [g/m2∙%RH] (“excellent” MBV performance according to the Nordtest protocol). A surface painting could further reduce the moisture buffering capacity of hempcrete: up to 14,1% with high and medium permeable latex paints and up to 78,6% with acrylic based paint.