The humidity buffer capacity of clay–sand plaster filled with phytomass from treatment wetlands

The aim of our study was to measure the amount of moisture absorption and desorption in clay-sand plaster mixed with "fibre-wool" from Typha spadixes and chips of Typha and Phragmites. Common cattail (Typha latifolia) and common reed (Phragmites australis) are the most common plants in constructed and semi-natural wetlands for wastewater treatment, as they are highly valued in ecologically oriented construction. The cattail and reed for the experiment were harvested in a wastewater treatment subsurface flow semi-natural wetland and in two free water surface constructed wetlands which showed reliable aboveground phytomass production over a 5 years period (for Typha, 0.37-1.76 kg DW m-2 in autumn and 0.33-1.38 kg DW m-2, and for Phragmites, 0.61-1.32 and 0.61-1.02 kg DW m-2, respectively). The quantity of moisture absorption and desorption was measured in a climatic chamber where the humidity of ambient air was suddenly raised from 50% to 80% (absorption) and reduced from 80% to 50% (desorption). Over 12 h, all of the samples released the same amount of water as they absorbed. The clay-sand plaster samples absorbed slower than they desorbed, whereas the gypsum wallboard required significantly more time for desorption. Added phytomass gave positive effects by reducing the weight of the clay-sand plaster, accelerating and increasing moisture absorption.