Moisture uptake and technical drying of cross-laminated Timber (CLT) Walls

Abstract

During construction, rain can cause unprotected CLT panels such as walls to absorb water, especially through the end-grain on the narrow sides. Practical experience shows that in such cases, the moisture content (MC) in the lower centimetres of the wall rises well above fibre-saturation. Within a sub-project of a larger research programme, we examined the long-term water absorption of five-layer CLT walls and the wood’s response to both technical and natural drying. Two test series were carried out: in both series the several CLT-walls were immersed 1 cm deep in water for 21 days and then dried. The series differed in the type of bonding, the external climate, and the support (with or without foam-rubber). Because technical drying has received little research attention, we evaluated convection drying and diffusion drying. In series 1, convection drying resulted in rapid drying of the walls, as moisture was quickly removed through a narrow gap under the wall. In series 2, a modified support (foam rubber) prevented air flow, extending the drying time. Diffusion drying, proved to be ineffective and was abandoned after series 1. The overall drying effort was high, indicating that early protection of CLT is essential. The use of coatings or timber-protection membranes to safe the panels from moisture ingress were investigated in another sub-project.