Case 2

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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 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.

Paint

Material

Use of a paint system, which allows moisture to pass through the coating to reduce the moisture pressure is another alternative to minimize paint defects caused by moisture [1-7].

Construction

Prior to the application or re-application of paint system, surface condition should be checked. Surface condition for painting process should be as follows[7-9]:

  • For new plaster, the plaster surface should be allowed about 30 days for proper curing and the reduction of moisture content. Further, it will need to be primed. The type of primer used will depend upon the final decoration required. If you plan to use oil-based paint, an alkaline-resisting primer should be used. For water-based paints, a diluted first coat can be used to prime.
  • For old surface, the preparation required will depend upon the condition of the surface. If it is clean, dry, and sound it will require no special preparation. However, if the surface is powdery or there is other evidence of old distemper residue, it should be dusted off and sealed with a stabilizing solution.
  • For the painted surfaces, the existing paintwork should be washed down first. This is necessary to remove traces of dirt and grease, which would otherwise cause failure of subsequent decoration.
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Figure 1
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Figure 2
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Figure 3

Light sanding with fine-grade, preferably part-worn, sandpaper would be able to remove ‘nibs’ and adherent dust particles, and to assist adhesion or provide a smooth level surface (Figure 1). Remove all loose and foreign particles by manual cleaning with scraping for painted surfaces (Figure 2).

Check the moisture of the substrate(Figure 3). The moisture content should not be more than 6%.

Quality Control

Quality assurance can be carried out as below:

STAGES OF WORKCHECKCRITERIA
Recognition of environmental conditionsTemperature of siteAmbient temperature > 5 °C or refer to manufacturer’s recommendations
Substrate temperatureSurface temperature of substrate < 60 °C or refer to manufacturer’s recommendationsSurface temperature of substrate > 3 °C + ambient temperature or refer to manufacturer’s recommendations
Relative humidityRefer to manufacturer’s recommendations
Checking of Surface PreparationMethod of surface preparationComply to approved submission
Prepared surfaceFree from foreign and unstable matters such as dust, dirt, rust, cement, spatter, salt, grease and oil
Mixing of paintMixing ratioComply to specificationSufficient stirring until uniformity
Painting controlSurface just before paintingPainting should start preferably within 24 hours after preparation
Protection to elements not to be coatedMask or cover those elements not to be coated
Process of applicationComply to approved submission
Intervals between coatsRefer to manufacturer’s recommendations
Wet film thicknessRefer to manufacturer’s recommendations

Source: BCA (2001b) Good Industry Practice-Painting

Reinforcement

Design

Sufficient concrete cover should be provided to prevent corrosion of reinforcement due to the ingress of sulphates and chlorides (Table 2).

Material

All high yield reinforcement bars should comply with SS 2 and welded steel fabric should comply with SS 32 [5]. Reinforcement can be protected further by using following methods:

  • removal of rust and mill scale before embedment
  • use of non-metallic coatings such as epoxy resins and solvent containing acrylic resins[6]
  • use of metallic coatings such as zinc and nickel[2]
  • Cathodic protection[3]
  • use of corrosion inhibitors
  • use of corrosion resistance reinforcement (eg. stainless steel)[2]
  • use of low permeability concrete, with improved resistance to chloride ion ingress

Water repellent and surface coating system

Clear water repellents are most effective at reducing the amount of water absorbed by the brick masonry. Thus, they can help reduce staining and fungi growth caused by moisture absorption, particularly on highly absorptive masonry.

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

  • cleaned by grinding, chemical etching or blasting.
  • 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:
    • Prevent penetration of water and solutions into brick without hindering the escape of internal moisture from concrete
  • Materials used [3]:
    • silicon organic solutions
    • resins
    • oils
  • Sealers
    • Heavy barrier against penetrating solutions but may hinder the escape of internal moisture
  • Materials used [3]:
    • 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 [3]:
    • plastic modified cement systems and resins