Common quality problems with plastering mortar and how to deal with them

1.Hollowing: The main causes are:
①unclean base treatment, such as dust and loose objects attached to the surface of the base, release agents and oil stains, etc. If these impurities are not completely removed, it will affect the adhesion between the plastering layer and the base.
②There are concave areas or the first layer of plaster is too thick, etc., and before the mortar dries, the mortar layer has already separated from the base due to gravity.
③The interface is not properly treated or not treated at all, the base surface is too smooth, and the dry shrinkage of the mortar cannot be suppressed, causing the mortar layer to separate from the base. Before plastering, the base should be cleaned, and water should be sprayed onto the wall 2-3 days in advance. After the water seeps to a depth of 10 mm, construction can begin. If there are deep concave areas, the mortar should be filled in advance. In addition, the interface mortar should be sprayed in advance.

2. Delamination: mainly due to the underlying layer of plaster being too dry. Prevention methods: In addition to construction according to specifications, if the underlying layer is found to be dry, it should be moistened with clean water, and the surface layer should be plastered after the underlying layer is thoroughly moistened.

3. Blasting: The main reason is poor material quality, with impurities or soil. The quality of the materials should be carefully checked before construction, and the sand should be sieved through a fine sieve before use.

4. Cracks: The main causes are an excessively thick plaster layer without crack-resistant measures or cracking due to hollowing. If the plastered surface is very thick, the base layer should be filled first during construction, or a crack-resistant agent should be sprayed after the base plaster is applied. If the above situations occur in cement plastering mortar, the work should be reworked and repaired. When repairing, remove the delaminated, hollowed, crumbling and cracked parts cleanly, and then plaster the local area according to the specifications.

Common problems and solutions for floor mortar

1. Cracking: Cracks appear on the floor due to changes in temperature (thermal expansion and contraction), or because the base layer is very damp. During the setting process, the floor mortar reacts chemically with some of the water, while the rest evaporates. The volume of the mortar shrinks after the water evaporates, causing the floor to crack. Therefore, the base layer should be cleaned in advance, and watering should begin 2-3 days in advance to keep the floor damp and free of standing water. In addition, the setting time of the floor mortar should not be too long.

2. Sanding of the floor: ① Water bleeding from the mortar causes the fly ash and other admixtures with lower density in the mortar to float, resulting in sanding. ② An unreasonable mortar mix ratio and excessive admixture will result in poor wear resistance of the surface of the mortar and sanding. Therefore, when designing the mortar mix ratio for the floor, it is necessary to design it in combination with the construction environment, and it is not enough to blindly believe that the laboratory data meets the standard requirements.

3. Insufficient mortar strength: An excessively high water-cement ratio results in a high consistency, which reduces the strength and hardness of the surface of the floor mortar and affects the wear resistance of the floor. During mixing, the amount of water used for the floor mortar should be strictly controlled to keep the consistency between 45-55mm.

Problems caused by segregation of dry-mixed mortar

1. In the bulk mobile silo, the mortar in the part of the bulk mobile silo that is just beginning to discharge and the last part to discharge is prone to segregation. Solution: Keep the amount of dry-mix mortar in the mobile bulk silo on the construction site at no less than 3 tonnes to prevent segregation caused by the large difference in discharge height when the dry-mix mortar is discharged into the mobile bulk silo.

2. Dry-mix mortar in storage tanks and transport vehicles is prone to segregation. Solution: Store dry-mix mortar in storage tanks and transport vehicles as full as possible and transport it at a constant speed and in a stable manner.

3. Slow loading and unloading speeds cause dry-mix mortar to segregate easily. Whether loading trucks, pumping materials, or unloading from storage tanks, the loading and unloading volumes should be large and the speeds fast. Experiments have shown that the phenomenon of dry-mix mortar segregation is more serious when the material volume is small and the unloading speed is slow than when the material volume is large and the unloading speed is fast. Solution: Increase the aperture of the silo discharge port to speed up the unloading speed.

4. The mixer under the bulk mobile silo has a small capacity and mixes a small amount of material, which is also the cause of the slow discharge speed and poor mortar quality. Solution: Consider modifying the capacity of the mixer under the bulk mobile silo or installing a large-capacity mixer.

Quality problems caused by dry-mix mortar production units

1. The excessive clay content or fine sand in the sand causes the dry-mix mortar to crack.

Solution: Control the clay content and fineness of the raw sand and use medium sand as much as possible.

2. The dry-mix mortar production unit did not adjust the mortar mix ratio in a timely manner in response to changes in wall materials, temperature, etc., causing the mortar to crack. Solution: Adjust the production formula in a timely manner according to different environmental temperatures, different wall materials, and other conditions. For example, if the temperature in summer is as high as 30°C, when plastering the wall of a light aggregate block, the mortar needs to have a higher water retention rate, and the amount of additives in the mortar should be adjusted appropriately to increase the water retention rate of the mortar.

The construction unit did not operate according to the specifications

1. The plaster was applied too thickly in one go during construction, causing the mortar to crack. Solution: Operate according to the specifications and do not apply the plaster too thickly in one go. For example, the specifications for the thickness of external wall plaster require that the thickness of each layer should be 5–7 mm each time. If the total thickness of the plaster is greater than 35 mm, strengthening measures should be taken.

2. Mortar applied to a substrate or base material with an inappropriate strength grade, or mortar shrinkage inconsistent with the base material, causing dry-mix mortar cracking. Solution: Use mortar of an appropriate strength grade for each type of wall material.

3. No measures taken at the junction of different materials, causing dry-mix plastering mortar to crack. Solution: Reinforced mesh should be used at the junction of different materials.

4. No watering or excessive watering of masonry, causing cracks and fissures in dry-mix plastering mortar. Solution: Follow the construction specifications, such as wetting sintered bricks and autoclaved fly ash bricks before plastering.

5. Masonry such as autoclaved bricks is constructed and plastered before reaching the required age, causing cracks in the dry-mix plaster. Solution: All block materials must reach the required age and be stable before use. For example, the age of autoclaved bricks before use should not be less than 28 days.