Wall plastering mortar that lacks sufficient strength or fails to meet grade standards often leads to issues such as sanding, powdering, hollow drum cracking, and surface unevenness. Many people tend to view these as signs of a poorly constructed “tofu-dregs project.” In reality, when such problems arise, contractors are often more concerned than the property owners. However, if these issues are only superficial, the situation may not be as severe as it seems. As long as the main structural integrity remains unaffected, these problems are relatively straightforward to address.
Sanding and powdering on walls are primarily caused by low-strength plaster mortar or substandard grading. On the other hand, blistering or cracking in the mortar layer may actually result from excessive cement content or overly high mortar strength—particularly in the case of cracking. (It is important to note: a distinction must be made between cracks in the mortar layer and cracks in the main wall structure. The latter is not discussed here.)
How to resolve hollow drum cracking in the mortar layer?
Hollow drumming in the mortar layer generally refers to inadequate bonding between the wall base and the plaster mortar, or insufficient compactness of the mortar leading to delamination. When hollow drum cracking occurs in the mortar layer—excluding issues with the main wall structure—it is often due to excessively high mortar strength, typically caused by an improper cement-to-sand ratio with too much cement. Observations during construction often show that the higher the mortar strength, the more frequent and noticeable the cracking.
To address sanding issues, begin by removing loose sand and dust from the wall surface. Evenly mix the wall sanding repair solution and spray it onto the wall, ensuring the surface is thoroughly moistened without causing runoff. For walls with moderate to severe sanding, apply a second spray after 30 minutes (or 10–20 minutes for highly absorbent surfaces, depending on site-specific tests). After 8 hours, inspect the results. If certain areas remain unresolved, analyze the cause or apply a third spray of filler.
In cases where sanding is caused by weathering,cement in the plaster mortar (or insufficient cement content), or excessive soil content in the sand, the effectiveness of repairs may be limited. For such walls, the old plaster layer should be completely removed and replastered.
