Case 3
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Good Practices
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.
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 WORK | CHECK | CRITERIA |
| Recognition of environmental conditions | Temperature of site | Ambient temperature > 5 °C or refer to manufacturer’s recommendations |
| Substrate temperature | Surface 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 humidity | Refer to manufacturer’s recommendations | |
| Checking of Surface Preparation | Method of surface preparation | Comply to approved submission |
| Prepared surface | Free from foreign and unstable matters such as dust, dirt, rust, cement, spatter, salt, grease and oil | |
| Mixing of paint | Mixing ratio | Comply to specificationSufficient stirring until uniformity |
| Painting control | Surface just before painting | Painting should start preferably within 24 hours after preparation |
| Protection to elements not to be coated | Mask or cover those elements not to be coated | |
| Process of application | Comply to approved submission | |
| Intervals between coats | Refer to manufacturer’s recommendations | |
| Wet film thickness | Refer to manufacturer’s recommendations |
Source: BCA (2001b) Good Industry Practice-Painting