Case 1

Good Practices

Plastering

The risk of crazing should be minimized by:

• The use of properly graded sand, in particularly the avoidance of an excessive proportion of a very fine material. The plastering sand used maybe of poor quality. With the wide use of ready mix plaster in Singapore, this defect has been greatly reduced.
• The use of a mix which is relatively lean in cement. This practice can be enforced with the use of ready mix and proper installation through manufacturer’s installation guides.
• The avoidance of overworking, which causes an excess laitance to be drawn to the surface.
• The avoidance of too rapid drying out of the plastering coat. This can be prevented by dampening before and during the application of plaster especially on high absorption rate background or in hot and dry environment. Hence for the application of plastering coat, care must be taken in the awareness of the different types of background and their absorption.
• During the curing of plaster, rapid loss of moisture from the plaster in hot weather can be reduced by covering the plaster or regularly wetting the plaster.
• For ready-mix plastering coat, to prevent rapid shrinkage of coating, the amount of water mixed should follow manufacturer’s specification.

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: