Tensile cracking of ventilated rendered rain-screen cladding systems

Ventilated and rendered rain-screen cladding (VRRC) systems are increasingly used in refurbishment of existing and construction of new buildings. Knowledge concerning different VRRC systems’ ability to withstand tensile cracking is however limited and critical levels of thermal or moist induced loads seldom stated in a quantitative way. The research presented in this paper deals with tensile cracking of VRRCs with cement based carrier boards. Laboratory experiments have been carried out to study parameters influencing tensile cracking of VRRCs. The testing involved direct tensile tests on specimens representing joints where the carrier board is fastened to wooden laths. In specimens manufactured according to the standard procedure a plastic zone formed close to the joints at imposed deformations corresponding to 0.7-0.8 mm/m. The first visible cracks formed outside the joint zone at imposed deformation levels larger than 1.0 mm/m. Omitting joint reinforcement did not result in a significant change in cracking behaviour. In specimens manufactured by omitting the surface reinforcement large cracks appeared at imposed loads of 0.4 mm/m. Use of renders with dispersed fibre reinforcement does not limit appearance of large cracks. Shrinkage normally observed in cement based boards and renders seems not large enough to cause visible cracks in VRRCs. In order to verify this statement, mechanical behaviour of entire walls with VRRCs is to be simulated with realistic climate data and verified by suitable laboratory and field measurements.