Case 1

Good Practices

Design

The substrate for stone cladding plays a important part. 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 or equivalent.

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.

Detailing

• Window, door or abutment are points of weakness where tile edges can be exposed and water ingress can occur. Metal cappings or flashings can be used.
• Horizontally tiled surfaces should be avoided and openings should be set back within the elevations.

Structural Frame

• An understanding of the type of structural frame and the amount of movement that could be experienced is needed.
• Structural concrete to which the tiles adhere to creeps under dead load and live loads. Proper movement joints of about 10mm wide, horizontally at every floor level, and at about 4m centers vertically is needed. They should be as deep as the tile and adhesive, and filled with a stable sealant such as polyurethane. Proper movement joints must be incorporated to prevent overall shrinkage of the frame and to allow expansion of the tiling.
• The frame must be regular so that a thin coat of adhesive will be able to adhere tiles to the surface.
• The reinforcement bars within the concrete substrate should be inspected regularly for signs of corrosion as an unstable background would bring about failure of tile covering.

 Materials

• The suitability of a ceramic tile for external wall depends mainly on its water absorption rate and thermal expansion.
• The tile bed has to be sufficiently flexible to accommodate moisture and thermal movements. Cement based polymer latex or resin are suitable for tiles. The grouting material is normally of the same type as tile bed, compatible to the tile bed and the tile.
• Single-fired vitrified wall tiles (glazed or unglazed) are especially suited for external walls subject to thermal shock conditions on tropical climates. The ceramic tile can withstand short-term changes in temperature over a range of 0°C to 150°C because of its microstructural characteristics.
• The tiles shall be fully tested to meet the performance requirements stipulated in the contract before mass installation.

Movement joints

Movement joints are required in 4.5m intervals in areas in excess of 4.5m of external tiling.
For multi-storey construction, some form of deflection of the building can occur at lower levels as the building increases in height as loading increases accordingly. Hence, by selecting an appropriate level to commence tiling, movement due to deflection at the lower levels can be accommodated before tiling works begins.

Tile joints

• Joints should be filled with a grout of good adhesion and low shrinkage.
• The grout should be reasonably flush with the tile face to ensure adequate thickness.
• It must also be complete and flexible both at the time of installation and after.

Adhesion

• Clean the surface thoroughly to remove foreign particles accumulated on wall. This is to ensure that the bonding of the rendering will not be affected.
• If the bedding material is ordinary cement mortar, the surface (render) should be damped to prevent any suction of water from screed/ or render. However, if the bedding material is an adhesive (Figure 4b), the manufacturer’s instructions should strictly be followed. These instructions such as surface preparation, mixing and application of adhesives are clearly labeled on the packing.
• The substrate has to be sound and even so that the adhesive will have a stable background.
• The substrate needs to adequately roughened so that the adhesive will bond. Concrete is a difficult surface to bond plaster to. It is hard, smooth and dense and will require careful and thorough preparation. Brick infill may be slightly easier. If mechanical roughening of the concrete cannot be adequately achieved then it may be advisable to plaster on to mechanically secured stainless steel mesh.
• The adhesive used should cover the tile completely and should be applied using the correct mix, thickness and consistency. It should also be ensured that retarders or parting oils are removed from concrete faces prior to tiling.
• Tiles should also be lightweight. Tiling should also not be done over existing tiling.
• Cleaning and roughening the surface of substrates is very important to ensure good adhesion of tile bed. It is good practice to limit the rendering layer to 20-25mm. If further thickness is needed, use reinforcement in a form of a lath or a wire mesh.
• On-site tests such as pull out test for anchors can be done to ensure the required strength stated by the specifications is met.