Study of a hemp concrete wall exposed to outdoor climate
Tuesday, 10 January 2017
French researchers have exposed cement based hemp concrete walls for one year to indoor controlled and outdoor climate. The objective of the study was to analyse the behaviour of the walls in realistic conditions.
Hemp concrete is becoming a popular building construction material, as it has a low environmental impact and helps reducing the heat conductivity of walls. The generally used binder is lime, but in this study a prompt natural cement binder was used.
Two exterior coatings were applied
Two test walls made of prefabricated hemp concrete blocks were built. Those walls were exposed to the outdoor climate on the one side, and to a controlled indoor climate on the other side. Two different exterior coatings were applied. The experiment lasted one year. In addition, numerical simulations were carried out. The model was used to determine the material properties and to help understand the behaviour measured.
Drying can last several month
The results show that an important humidification of the wall can occur if the coating is not well chosen. The exterior coating must be very permeable to water vapour, but it seems to be important to prevent the absorption of rain as well, otherwise, the humidity inside the wall can lead to degradations such as mould growth or increased thermal conductivity. Both numerical simulation and measurements show that applying a vapour permeable coating on the blocks does not slow down the drying process, the hempcrete itself being the limiting factor.
The study is published in: Construction and Building Materials.