Case 2
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Good Practices
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 to ensure 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 inaccordance with BS 6150, SS 542 or equivalent. Ensure access ducts are connected to the mechanicalventilation system. The exhaust system shall dispel the air directly outdoors.
The stone should be sealed so that moisture could not penetrate the stone easily. By cutting off water, biological growth cannot be sustained.
Sealers for stones should be applied to prevent water from being retained in the pores of the stones. Sealers should have the following properties:
- virtually odourless
- non yellowing
- deep penetrating protection
- weather resistant
- maximum stain resistance.
Keep dense vegetation and low hanging branches clear from the façade.
Water shedding features should be incorporated to throw water off and prevent runoff from running down the façade. The period where the wall remains damp after a rainfall should be kept as short as possible.
Dampness
Prolonged dampness on a facade is determined, among other, the following:
(1) Rainwater runoff pattern
(2) Water absorption coefficient and texture of the material
Water absorption affecting staining
Source: Flow and Changes in Appearance, 1996
For more information on staining issue on facade, please visit “Staining of Facades“.
Recommendations for Treatment
Use only an approved surface biocide. Apply the biocide in compliance with the manufacturer’s instruction, avoiding application during or shortly before rain. Avoid over-application as run-off could damage adjacent vegetation or contaminate water courses.
Where a significant thickness of surface growths is present, maximum efficacy can be obtained by following initial biocide application with a dry brushing procedure to remove growths which have died, and then re-treating with biocide. Where growths are superficial, not forming a thick layer, and only unsightly, the additional cost of cleaning and re-treating is generally not justified on the sole basis of improved performance.
On relatively sheltered sites re-treating may be needed at intervals of about 5-10 years and on exposed sites after 3-5 years.