Case 1

Good Practices

Some backing walls are more liable than others to give rise to cracking of the rendering. On such backing walls precautions should be taken to control the incidence of cracking.

Backing wall of masonry should be divided into panels to accommodate movement. A straight joint should be formed in the plastering coincident with the joint in the background and with the resultant subsequently sealed with a suitable joint sealant.

For rendering on metal lathing, which is subjected to movement, the plastering should also be divided into panels at intervals of approximately 5m.

Design

Tall slender concrete structures should be designed with due consideration of the effects of lateral deflection and be within acceptable vibration limits in accordance with BS EN 1992-1-1, SS EN 1992-
1-2, CP 65-1 or equivalent. Any deflection/deformation of the concrete structure due to vertical loading
should be compatible with the degree of movement acceptable by other elements (i.e., the finishes,
services, partition, glazing and cladding) in accordance with BS EN 1992-1-1 or equivalent. Limit State Method should be considered for design and verification of structure for durability of façade structures. Refer to modelling of deterioration process in accordance with ISO 13823 or equivalent.

The causes, effects and methods of prevention and repair for cracks (e.g., longitudinal cracks, transverse
cracks, cracks above prestressing strands, web crack at or near the prestressing strands, corner crack, and miscellaneous cracks) in precast concrete wall panels should be considered and applied in accordance with BS EN 13369, SS 677 or equivalent. Limit the design crack width with reference to CP 65-2 or equivalent. Laboratory mechanical tests should be carried out to measure deformations on horizontal joints between load-bearing walls and concrete floors in accordance with ISO 7845

Construction

Use two-stage joints for precast façade construction to ensure higher watertightness performance, since doing so will avoid seepage through hairline cracks, as is the case with one-stage joints in accordance with SS EN 1992-1-2 or equivalent. Seal off horizontal joints for load bearing walls with non-shrink grout.
Minimise cracks in rendered brick walls by using appropriate mix ratio, thickness and number of coats.
Provide bonding bars at interfaces between different materials in order to minimise cracks (e.g., where a brick wall abuts concrete). Alternatively, the bonding bars can be cast together with the concrete member.

At the completion of the construction stage, minor repair work or fixing adjustments may be acceptable. Enhance the durability of vulnerable parts of construction; ensure that surfaces exposed to water are freely drained; provide adequate cover to steel; use protective coatings for either steel or the concrete, or
both in accordance with BS EN 1992-1-1, SS EN 1992-1-1, SS EN 1992-1-2, CP 65-1 or equivalent. Make accessible components of which predicted service life is less than the design life of the structure for inspection, and replace them in accordance with ISO 13823 or equivalent.