Case 2
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Good Practices
Dampness
Design
The material selection for exposed surfaces, and their regularity and surface texture should be detailed to
prevent moisture retention. Areas prone to high moisture exposure shall be made impervious with adequate waterproofing systems. Also such surfaces should be without impediments (e.g. built-in cabinet, fixed equipment/services) to ensure access for inspection and ease of cleaning. Access for adequate cleaning should be provided in accordance with BS 8221- 1, SS 509-1 or equivalent. Ventilate to prevent moisture retention on floor/wall/ceiling. For natural ventilation, opening > 5% of floor area. For mechanical ventilation, air exchange rate > 20 air changes per hour, in accordance
with “CP on Environmental Health”.
Construction
Exterior surfaces of porous building material (e.g., cellulose, brick, stone, cement rendering) can develop biological growth. Avoid such growth as much as possible with treatments of anti-algae/anti-fungus solutions and allow to dry before painting/repainting (SS 652: B.5.2.1). Improve ventilation and remove sources of dampness to dry out the substrates as thoroughly as possible during painting works in
accordance with BS 6150, SS 542 or equivalent. Ensure access ducts are connected to the mechanical
ventilation system. The exhaust system shall dispel the air directly outdoors.
Brick Wall
Design
A suitable wall thickness and finishes such as plaster or water repellents or other coatings should be provided to improve the water-tightness of the brick wall. E.g. wall rendering consists of cement and sand mix in the ratio of 1:3 to 1:5.
Material
Suitable finishes can be used to enhance the water-tightness of the brick wall. A suitable cement mortar mix should be used to minimise water penetration through mortar joints. The cement mortar should possess the desired characteristics of high water retentivity, high plasticity, good adhesion and should not shrink excessively during and after hardening. Table 1 recommends some plaster mix proportions.
| Mix | Mix proportions by volume based on damp sand | ||||
| Cement : Lime : Sand 1) | Cement : Ready-mixed lime/sand 1) | Cement: sand 1) (using plasticizer) | Masonry cement: sand 1) | ||
| Ready-mixed lime:sand | Cement: ready-mixed material | ||||
| I | 1 : ¼ : 3 | 1:12 | 1 : ¼ : 3 | – | – |
| II | 1 : ½ : 4 to 4 ½ | 1:12 | 1 : ½ : 4 to 4 ½ | 1 : 3 to 4 | 1 : 2 ½ to 3 ½ |
| III | 1 : 1 : 5 to 6 | 1:12 | 1 : 1 : 5 to 6 | 1:5 to 6 | 1 : 4 to 5 |
| IV | 1 : 2 : 8 to 9 | 1:12 | 1 : 2 : 8 to 9 | 1:7 to 8 | 1 : 5 ½ to 6 ½ |
| V | 1 : 3 : 10 to 12 | 1:12 | 1 : 3 : 10 to 12 | – | – |
| 1) With fine or poorly graded sands, a lower volume of sand should be used. Note: In special circumstance, e.g. where soluble salts in the background are likely to cause problems, mixes based on sulphate-resisting Portland cement should be employed. | |||||
Non-film forming water-based polymeric impregnating agent is used impregnate the brickwall to reduce its water absorption properties.
The following waterproofing coatings can also be used for fair-faced brick wall or walls exposed to more severe weather condition or subjected to frequent impingement of rainwater from the roof
- Plaster mixed with waterproofing admixtures
- Elastomeric paints
- Cementitious coating
- Water-repellent coating such as silane
Construction
- Particular attention should be paid to ensure that the joints are properly grouted and to be free of voids. For joints between brick wall and reinforced concrete wall like this case, there should be bonding bars secured to or cast in the reinforcement concrete wall and be extended into the brick wall. The bonding bars are important in minimizing cracks along the joint.
- Brick units should be thoroughly wetted before laying to reduce the absorption of water from the mortar thus, reduce the risk of mortar cracking.
Painting (internal)
Material
Select an appropriate paint which has fungi-resistance. There are many paint systems available in the industry.
Quality Control
Checklists for paint work can be used as means to enhance onsite workmanship quality [18].
Ventilation
Design
- Good ventilation of wet areas is necessary to keep the place dry and remove excess moisture. With dry conditions, the growth of fungi will be inhibited [19-20].
- Adequate ventilation should be provided to enhance the drying process. Proper air circulation can be designed by natural, mechanical or a combination of both mechanical and natural ventilation systems in which minimum air change per hour (ACH) should be 10 [21]. However, if entirely mechanically ventilated systems, minimum ACH should be 15.[22]