Hebel is extremely absorbent. Put a standard cement render on it and the panel pulls the water out of the mix before the cement has hydrated, which leaves you with a weak, powdery render that has never properly gained strength. It has to be rendered with a system made for it.
Why Hebel needs its own render system
The suction is the issue. A dry Hebel panel will draw the mix water straight out of a conventional render within minutes. Cement needs that water to cure, and without it the render simply never reaches strength. It looks fine on the day and it comes away in your hand six months later.
The purpose made systems get around this with polymer content that holds water in the mix, plus a base coat designed for a high suction substrate. On some jobs the panel is also dampened or primed first, depending on conditions and the manufacturer's specification.
We follow the panel manufacturer's system. That matters for warranty as well as performance, because using non specified products on Hebel can void the panel warranty.
Joints, corners and mesh
Like blueboard, Hebel is a panel product with joints, and joints are where movement concentrates. The system includes mesh reinforcement in the base coat, with additional reinforcement at panel joints and at every window and door corner where stress is highest.
Hebel corners also need proper corner beads. The material is soft enough that an unprotected external corner will chip if something knocks it, and once the render corner is damaged the repair is visible.
Where we see Hebel in Sydney
Mostly on first floor additions, particularly across the North Shore and the Hills where adding a storey to a single storey brick home is the standard renovation. The weight saving over brick is the deciding factor.
Also increasingly on new builds through the south west growth corridor, on party walls between attached dwellings where its fire and acoustic rating is useful, and on granny flats.