Case 1
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Good Practices
Plastering
Material
Use properly graded sand and in particular, avoid excessive proportion of a very fine material. With the wide use of ready mix plaster in Singapore, the occurrence of this defect has been greatly reduced.
Construction
The following practices can be followed-up to minimize crazing during construction:
- Prevent rapid drying out of the plastering coat by dampening before and during the application of plaster especially on high absorption rate background.
- Avoid overworking, which causes an excess laitance to be drawn to the surface.
- Start curing the plaster as soon as possible and continue it for a minimum of 3 days. During the curing of plaster, rapid loss of moisture from the plaster can be reduced by covering the plaster or regularly wetting the plaster.
Quality Control
Avoid the following during plastering to minimize crazing:
- Do not dust any cement onto the surface to absorb bleed water.
- Do not sprinkle water on the surface while finishing.
- Do not trowel excessively as it will draw the water to the surface.
Painting
Construction
Prior to the application or re-application of paint system, the surface condition should be checked. Surface condition for painting process should be as follows[3-5]:
For new plaster, the plaster surface should be allowed about 30 days for proper curing and the reduction of moisture content. Also, it will need to be primed. The type of primer used is dependent on the final decoration required. If you plan to use an 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 on the condition of the surface. If it is clean, dry and sound, no special preparation is required. However, if the surface is powdery or there is 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.
Quality Control
Quality assurance can be carried out as below:
| STAGES OF WORK | CHECK | CRITERIA |
| Recognition of environmental conditions | Temperature o f 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 |
For more information on paint crazing due to moisture, please refer to Paint Blistering, Peeling & Flaking.