Case 1

Good Practices

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 runoff within joints and expansion joints designated to provide vertical runoff carrying dirt down along the façade surface. Specify façade selfcleaning 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 “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.

Plastering

• If the background is known to contain appreciable amounts of soluble salts (especially sulphates) and may remain wet for prolonged periods of time, the plastering may deteriorate due to chemical action between the salt and cement in the plastering or in the mortar joints.
• Damage may result during the crystallization of soluble salts. The limits for soluble salts given in BS 3921 provide a useful guide for clay bricks.
• The leaching of soluble salts can be reduced by the use of sulphate-resisting Portland cement for plaster mix.
• The use of water resistant ready mix plaster may also reduce the occurrences of such efflorescence provided that it is used in areas where the internal areas are of high moisture content.