Case 4

Good Practices

Avoiding or minimising staining involves good design practices from the onset.

The method of fastening by which the fixture is attached to the façade has a large effect on the intensity of staining.

Allowing a clearance between the signage and the façade may be considered good practice as it minimises disruption to the even flow of runoff on the façade. The clearance left between the fixture and the façade must be wide enough to prevent debris and large dirt particles from collecting within the clearance gap.

Disruption of even and regular runoff flow on the façade will be minimised and dirt that gathers on the protrusion cannot be washed onto the façade. In addition, the attachments should be made to be as small in dimension as possible and should ideally be made of materials that do not corrode.

Instead of fixing the letterings and signage tightly to the wall, they may be fixed by means of small-dimensioned bolts with clearance allowed between the façade and the fixture (Figure 2). In this way, disruption of runoff flow would be significantly minimised. The attachment points would also gather minimal dirt.

Runoff would be able to flow undisturbed and staining below the protrusion would be minimised.

When selecting the material of attachment, more attention should be paid to its durability. Materials that would rust easily should not be used.

Some contractor teams may overlook such consideration. Consequently, staining may result from the attachment materials corroding, rather than dirt accumulation and redeposition.

Design

Specify material and application methods for water repellence of porous masonry in accordance with BS 8221-2, SS 509-2 or equivalent. Throw off water from the façade altogether through an outward projecting sill or overhanging eaves (which incorporate a throat or drip lines on its underside) or provide blocking features such as copings/flashings. Use efficient scupper drains/downpipes to channel water down and away from the façade. To provide drip grooves along the underside of projecting features. Specify a paint system, which is permeable to avoid any paint defects which may cause staining.

Render the detailing for open joints as opposed to butt joints to avoid sealant staining. To use nonbleed sealants so as to prevent staining from silicone oil. Recommend joint designs, which are able to retain rainwater runoff within joints and expansion joints designated to provide vertical runoff carrying dirt down along the façade surface. Specify façade self-cleaning applications (e.g., TiO2, superhydrophobic
paint products, etc.) with due consideration given to site orientation, sunshades and protruding features. To understand the impacts of environmental, material, design and maintenance aspects on rainwater runoff.

See also Staining of Facades

Construction

Paint façade surfaces evenly with no patchiness. The finished texture should be uniform in colour. Ensure proper rendering to control surface granularity and local faults as it influences colour uniformity of the external façade in accordance with ISO 7361 or equivalent. Correct sealant applications to ensure consistent and continuous quality. Avoid misaligned panels of cladding in accordance with BS 8000-0 or equivalent. Refer to the planning of the painting programme, including inspection regime (initial and routine inspections) for buildings in accordance with BS 6150, SS 542 or equivalent.

Use self-cleaning coatings on newly built substrates for increased success in its performance. All construction/repair works on a façade surface should be done prior to application of a water repellent in accordance with BS 8221-2, SS 509-2 or equivalent. For serviceability of exterior façade surfaces, adopt ASTM E1667-95a or equivalent. It is important as it dictates the building’s individual and corporate identity. The correct application of TiO2 coating is crucial to ensure proper adhesion to the substrate. It is also challenging to check the proper application of the coating, especially on high-rise buildings, due to
its transparent property.