Case 1

Good Practices

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 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.

Brick

Design

Design and plan well. Attention must be paid to waterproofing the brickwall. Important considerations to place on:

• Design recommendations
• wall types,
• workmanship characteristics,
• detailing, flashing,
• drips and weep holes (Figure 1)

Allow sufficient joint size between bricks.

Expansion joints should be allowed at regular intervals of the brickwall.

Interface between brick wall and other components such as windows or other materials should be given sufficient allowance for movement (Figure 2). The use of sealant can accommodate the relative movement at the interface.

Material

• Selection of bricks should meet the requirements of relevant standards.
• All bricks should be accompanied by the manufacturer’s certificate.

Construction

• Workmanship characterized by the complete filling of all mortar joints intended to receive mortar is desirable, as is the need to keep all cavities clean and free of mortar droppings.
• Attention to both of these items is of primary importance in preventing moisture penetration to the interior of masonry.
• Protection
• Partially completed masonry walls exposed to rain and other elements during construction may become saturated with water and can require weeks, or even months (depending on climatic conditions), after the completion of the building for the masonry to dry. This prolonged saturation may cause many “slightly” soluble salts, as well as the highly soluble salts, to go into solution. Such conditions may also contribute to the contamination of the masonry with soluble salts from elsewhere in the construction (concrete, plaster, trim, etc.).
• During construction, all walls should be kept dry by covering with a strong, waterproof membrane at the end of each workday or shutdown period. These are used in conjunction with plastic sheets or water-repellent tarpaulin material and offer excellent protection for extended periods of time.

Quality control

Conduct water test to the external full height facing brick walls to test the water tightness of external wall construction [3].

Storage

Masonry units should be stored off the ground to avoid contamination by dirt and ground water, which may contain soluble salts.

Mortar

Design

Table 1: Mortar mixes and designations

Material

• Use prepacked mortar for consistency
• Mortar types and proportions should be selected on the bases of structural and exposure requirements for the particular project.

Construction

•  Mechanical mixing of prepacked mortar is advisable. Mixing time should be approximately 10 minutes to achieve good workability .
•  Fill all mortar joints solidly
• Clean all excess mortar from mortar joints.

Storage

Cementitious Materials

Cementitious materials for mortar should be stored off the ground and either inside or under cover.

Sand

Sand for mortar should also be stored off the ground to prevent contamination from dirt, plant life, organic materials and groundwater, any of which may be a contributor to efflorescence. In addition, it is advisable to store sand and other aggregates under a protective membrane cover, if possible.

Water repellent and surface coating system

Clear water repellents are most effective at reducing the amount of water absorbed by the brick masonry.

Surface preparation is important. The surface on which the coating is to be applied has to be:

1. cleaned by grinding, chemical etching or blasting.
2. dried by allowing the wall to cure for a few days before the coating is applied. During rainy periods, the walls should be protected with a plastic covering so that the drying is not interrupted.

Other surface protection systems include:

• Impregnation systems:
• Materials used:
  • silicon organic solutions
  • resins
  • oils
• Sealers
  • Heavy barrier against penetrating solutions but may hinder the escape of internal moisture
• Materials used:
  • epoxy resins (EP)
  • polyurethane resins (PU)
  • unsaturated polyester resins (UP)
• Coatings
  • compared to sealers, they provide additional protection against mechanical influence.
• increased resistance to diffusion of internal moisture
• Materials used:
  • plastic modified cement systems and resins

Window design

Selection

The manufacturer has to fully comply with the specification as set out in the SS 212. Specification for Aluminium Alloy Window.

Storage of window