Abstract
Experiments were carried out according to the Nordtest protocol to study the moisture buffer potential of hemp-lime walls with a range of different internal linings and surface treatments. It was observed that the moisture buffer value was ‘Excellent’ when the inner surface of hemp-lime was exposed. ‘Excellent’ moisture buffer values were also obtained for hemp-lime with lime plaster. All other assemblies demonstrated ‘Good’ moisture buffer value. Moisture buffer values of the assemblies, after application of paint on the upper surfaces, were also determined. It was observed that application of synthetic pigment based trade paint could reduce the moisture buffer performance of the assembly consisting of hemp-lime and lime-plaster from ‘Excellent’ to ‘Good’ while between 61 and 69% reduction of moisture buffer value was observed for the other assemblies. However, the reduced buffer values of the assemblies are still comparable with other moisture buffering building materials. It was further observed that moisture buffer performance was improved when clay based organic paint was used instead of trade paint.
Highlights
Hemp-lime is a bio-composite material comprised of hemp shiv, the woody core of hemp plant, and a lime based binder [1]
The results show that the application of trade paint on the surface of the assemblies decrease the moisture buffer value (MBV) value of Assembly 2 by 62%, Assembly 4 by 3.6%, Assembly 7 by 2.2% and increased the MBV values of Assembly 3 by 5.2%, Assembly 6 by 5.4%, Assembly 9 by 2.8% and Assembly 10 by 7.6%
It can be observed that the MBV value of Assembly 3 is 103% higher than that of the plaster board (PB), confirming that the hemp-lime in the assembly is actively involved in the moisture buffering of the composite assembly
Summary
Hemp-lime is a bio-composite material comprised of hemp shiv, the woody core of hemp plant, and a lime based binder [1]. Hemp-lime is a carbon-negative and low embodied energy material [2,3]. The dry thermal conductivity of hemp-lime varies between 0.06 and 0.12 W/m K [1,10,11]. It is observed that the thermal performance of hemp-lime is better than what its U-value or thermal conductivity value suggests [4]. This is may be because of the low thermal diffusivity of hemp-lime resulting from its high specific heat capacity [12], varying between 1300 and 1700 J/Kg.K [3], combined with its high density, ranging between 220 and 950 kg/m3 [13]. Since the external boundary conditions are dynamic, the high thermal mass of hemp-lime means that variations in changes in temperature can be dampened and the peak energy load can be reduced [14]
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