7 Quality Issues of Pre-Mixed Dry Mortar

2.1 Plastic Shrinkage Cracking

Cause: Plastic shrinkage cracking occurs during the early stages of the mortar setting when rapid moisture loss leads to shrinkage stress. Common causes include:

• High cement content
• Low sand fineness modulus
• High water-to-cement ratio
• Environmental factors like high temperature, wind, and low humidity

Preventive Measures:

• Reduce cement content and optimize the sand fineness modulus to improve mix consistency.
• Incorporate appropriate retarders and additives to slow down moisture evaporation.
• Monitor environmental conditions and take steps to control temperature and humidity during construction.

2.2 Drying Shrinkage Cracking

Cause: Drying shrinkage cracking happens after the mortar sets, primarily due to moisture loss and the associated volume shrinkage. Contributing factors include:

• High cement content
• Inadequate curing methods
• Mismatched elastic modulus between mortar and substrate materials

Preventive Measures:

• Use low-shrinkage additives and reduce cement content to minimize shrinkage.
• Implement proper curing techniques to maintain moisture levels during hydration.
• Ensure compatibility between the mortar and substrate materials to reduce the risk of cracking.

2.3 Clumping and Aggregation

Cause: Clumping of mortar results in reduced performance and inconsistent quality. Causes include:

• Insufficient drying of sand
• Short or uneven mixing times
• Variations in the quality of raw materials from production companies
• Lack of maintenance of mixing equipment

Preventive Measures:

• Enforce stringent quality control measures at production facilities to ensure consistency.
• Clean and maintain mixing equipment regularly to ensure thorough blending.
• Provide contractors with adequate training on proper material handling and mixing practices.

2.4 Non-Compliance with Test Block Strength

Cause: Inconsistent test block strength can indicate poor-quality mortar, often due to:

• Use of unqualified molds
• Improper curing and preparation of test blocks
• Non-standard testing methods

Preventive Measures:

• Train staff on proper testing and curing procedures.
• Ensure test molds meet industry standards.
• Regularly inspect and calibrate testing equipment to ensure accurate measurements.

2.5 Surface Detachment and Uneven Finish

Cause: Poor surface adhesion, which leads to peeling or sand shedding, is a frequent issue. Causes include:

• Excessively fine sand with high clay content
• Insufficient bonding agent content

Preventive Measures:

• Control the particle size distribution of sand, ensuring low clay content.
• Increase the proportion of cementitious materials and bonding agents to improve adhesion.

2.6 Inconsistent Setting Time

Cause: Variability in setting time can disrupt the construction workflow and schedule. Contributing factors include:

• Temperature variations
• Excessive moisture content
• Improper use of retarders

Preventive Measures:

• Adjust formulations based on environmental conditions and project-specific requirements.
• Monitor site conditions and control the use of retarders to maintain consistent setting times.

2.7 Water Separation and Surface Foaming

Cause: Water separation and foaming can occur due to poor mixing or excessive water content. Causes include:

• Inadequate mixing times
• Insufficient use of water retention agents
• Poor sand grading

Preventive Measures:

• Improve mixing time and ensure thorough integration of materials.
• Optimize sand grading and use sufficient water retention agents to prevent separation and foaming.