How to solve common problems with dry-mix mortar?

Shijiazhuang Qingquan Cellulose Co., Ltd. is a Chinese manufacturer of HPMC/PVA/CMC/MHEC/HEC. HPMC is one of our key products, known for its excellent quality and reasonable price, and can be used as a thickener/water retention agent in building mortars.

Mortar is exhibiting clumping and agglomeration on the construction site, resulting in a decrease in quality.

Reasons for the problem: The mortar manufacturer is using substandard raw materials, the sand's moisture content does not meet the requirements for sand drying, the mortar mixing time is too short, and the mixing is uneven; the construction company failed to protect the mortar from rain and moisture during storage, and did not clean the dry mortar silos and mixers in a timely manner, as required by pre-mixed mortar construction specifications.

Solutions: The mortar manufacturer needs to establish a comprehensive quality management system, strengthen control over the production process, and improve raw material testing; the construction company should strengthen the protection of dry mortar, improve quality control measures for mortar construction, and assign dedicated personnel to maintain and clean the dry mortar silos.

 Mortar Appearance Quality Problems

1. Mortar does not adhere well after application and easily falls off.

Reasons: Poor workability and low bonding strength of the mortar; the contractor applied too thick a layer of plaster at once, and the time interval between plastering layers was too short. Improper treatment of the substrate interface.

Solutions: Adjust the formula based on different raw materials and substrates to increase bonding strength; during construction, it is recommended to apply plaster layer by layer, with a total thickness not exceeding twenty millimeters, and pay attention to controlling the time of each process and ensuring proper interface treatment, especially for some new wall materials, which should use special matching mortar.

2. Mortar shows peeling, powdering, and sand shedding after application.

Reasons: Peeling and powdering are mainly due to the small fineness modulus of the sand used in the mortar, excessive use of admixtures, and excessive troweling during construction, which causes some powder to float to the surface and accumulate, resulting in low surface strength and thus powdering and peeling. Sand shedding is caused by a fineness modulus that is too small, as well as excessive clay content in the sand and a low proportion of cementing materials, which causes some sand to float to the surface and shed.

Solutions: Strictly control the fineness modulus of the sand, the grading of particles, and the clay content. Increase the amount of cementing materials, adjust the formula, materials, and proportions in a timely manner, and pay attention to construction techniques and curing measures.

3. Mortar surface is rough, lacks mortar, or the surface is uneven after finishing.

Reasons: The aggregate (sand) in the pre-mixed mortar contains too many large particles and has a high fineness modulus, resulting in less mortar and inability to achieve a smooth finish.

Solutions: Optimize and adjust the particle size distribution of the aggregate in the mortar, and appropriately increase the amount of powder.

4. Mortar shows hollowing, detachment, and penetration problems after hardening.

Reasons: Insufficient quality management and control by the manufacturer, leading to quality problems in the mortar product; poor construction quality by the construction company, not strictly following construction specifications, leading to usage problems; incompatibility between the interface agent and adhesive used for wall interface treatment and the dry-mix mortar; changes in ambient temperature causing expansion or contraction of building materials; cracking of the wall itself. Solution: Mortar manufacturers need to improve their quality control measures and responsibilities, and construction companies also need to improve their construction measures and responsibilities for mortar projects. Both parties should jointly provide relevant technical knowledge and skills training to production and construction personnel at key operational points.

Quality Problems of Mortar Cracks

1. Plastic Cracking

Plastic cracking refers to cracks that occur in mortar before or during hardening.  It generally occurs in the early stages of mortar hardening. Plastic cracks are typically coarse and short.

Reasons: This is mainly related to the material properties of the mortar itself and the ambient temperature, humidity, and wind speed. High cement content, smaller fineness modulus of sand, higher clay content, and higher water content all increase the likelihood of plastic cracking. Higher ambient temperature, lower humidity, and higher wind speed also increase the risk of plastic cracking.

Solutions: By adding water-retaining and thickening agents to the mortar, reducing the amount of cement, controlling the fineness modulus and clay content of the sand, reducing the water content, and controlling the construction environment to avoid high temperatures, dryness, and strong winds, the risk of plastic cracking can be reduced.

2. Drying Shrinkage Cracking

Drying shrinkage cracking refers to cracks that occur in mortar after hardening. It generally occurs in the later stages of mortar hardening. Drying shrinkage cracks are characterized by being thin and long.

Reasons: The main factors causing drying shrinkage cracking include high cement content in the mortar, resulting in excessive volume shrinkage; inadequate curing after mortar application; high drying shrinkage value of the admixtures or additives added to the mortar; cracking of the wall itself and improper interface treatment; misuse or incorrect use of mortar grades; and a large difference in elastic modulus between the substrate and the mortar.

Solutions: Reduce the amount of cement used, add appropriate admixtures to reduce shrinkage, strengthen the training and guidance of relevant construction personnel on professional knowledge, strengthen management, and strictly adhere to the pre-mixed mortar construction methods.

Efflorescence on Mortar Surfaces

Reasons: This is partly due to construction companies rushing to meet deadlines (mostly occurring in spring and winter), and also due to the use of early-strength admixtures containing sulfur tetroxide, chlorine, or composite products primarily composed of these substances.

Solutions: Use low-alkali cement and admixtures as much as possible, optimize the mix ratio, increase the density of cement-based materials, and reduce capillary pores. Avoid construction in windy, dry, or low-temperature conditions. Strictly control the amount of water added during mortar mixing. The flooring material should not bleed water during construction, and the surface should not come into contact with water before it is completely dry. Efflorescence inhibitors can also be used.

Unstable or Non-Setting of Mortar

Reasons:

(1) Mortar setting time is too short: This is due to high ambient temperature, excessive water absorption of the substrate, and low water retention of the mortar, resulting in a shortened setting time.

(2) Mortar setting time is too long: This is due to weather and seasonal changes, as well as excessive use of admixtures, resulting in a prolonged setting time.

(3) Mortar does not set: This is due to substandard cement quality or uncontrolled admixture dosage, resulting in water separation, significantly increased consistency, and failure to set.

Solutions: Adjust the type and dosage of admixtures according to different seasons, weather conditions, and wall materials; strengthen on-site inspections to obtain construction information promptly; strengthen the inspection and maintenance of metering equipment to prevent equipment damage and malfunction; strengthen the sense of responsibility of operators and quality control personnel, and strictly prohibit the shipment of unqualified products.