Full scale tests of moisture buffer capacity of wall materials

Moisture buffer capacity of hygroscopic materials can be used to moderate peaks in the relative humidity (RH) of indoor air as well as moisture content variations in building materials and furnishing. This can help to ensure healthier indoor environments by preventing many processes that are harmful such as growth of house dust mites, surface condensation and mould growth. Therefore a series of experiments has been carried out in a full scale test facility to determine the moisture buffer effect of interior walls of cellular concrete and plaster board constructions. For the cellular concrete, the buffer performance is investigated first for the untreated material, then after adding rendering on the surfaces, and finally with latex paint. Similarly for the walls of plasterboard construction, the buffer effects are investigated first for the insulation (cellulose or mineral wool), then after adding untreated plasterboards as cladding, and finally with additional latex paint. The walls were exposed to cyclic humidity variations like in an inhabited indoor environment, and the response of the indoor humidity was followed over time. The investigations also comprised simultaneous determination of the changes of moisture content in specimens of the wall composites exposed to the same environment. It was found that the finishes had a big impact on the buffer performance of the underlying materials. Even though the untreated cellular concrete had a very high buffer capacity, the effect was strongly reduced even with the supposedly highly vapour permeable rendering finish, not to mention the case when the latex paint was used. In the same way, the experiments for the plaster board construction demonstrated how cellulose insulation, as a very hygroscopic material, is a good buffer compared to the almost non-hygroscopic mineral wool. For example, it was found that if half of the surface area of the walls in a test room consists of cellulose insulation, the variation in RH can be reduced to nearly half of the variation seen for a similar room using non-absorbing materials and the same moisture load. However, subsequent tests demonstrate that for daily humidity variations it is not possible to take advantage of the moisture buffer capacity of the interior layers of a composite wall if the absorbing layers are covered with plasterboard, painted or not.