Why Do Cracks and Debonding Occur After Using Pre-mixed Plastering Mortar?

Pre-mixed plastering mortar is increasingly used in modern construction due to its stable quality, consistency, and eco-friendly advantages. Compared with traditional on-site mixing, it ensures better control of material performance.

However, in real projects—especially when plastering concrete shear walls—common issues such as cracking, hollowing, and debonding still occur. These are not material defects, but rather the result of construction practices not fully adapted to pre-mixed mortar.

If the base wall is not leveled, mortar thickness varies, causing uneven shrinkage and stress, which leads to cracks or detachment.

👉 Solution: Level the wall first, let it rest 5–7 days, then apply plaster.

When plaster is applied too thick at once, or under low temperature and wet conditions, the layer may slide down before hardening.

👉 Solution: Apply in layers (≤20mm each), avoid rainy or freezing conditions.

Hot weather or strong wind accelerates drying, resulting in early shrinkage cracks.

👉 Solution: Avoid direct sunlight, schedule plastering during cooler hours, and ensure proper curing.

At the junction of masonry walls and concrete beams, varying absorption rates cause stress differences and cracks.

👉 Solution: Use steel mesh or fiberglass mesh at interfaces before plastering.

Corners, windows, and door openings experience different constraints, leading to cracks.

👉 Solution: Reinforce corners with mesh to reduce stress concentration.

If the bonding (interface) layer is not strong enough, later shrinkage pulls the plaster away from the substrate.

👉 Solution: Roughen or prime the surface, strengthen bonding layers, and plaster in multiple coats for thickness >20mm.

Pre-mixed plastering mortar is a reliable, high-quality alternative to traditional site-mixed mortar, but it requires:

By combining the right materials with the right techniques, construction teams can avoid cracks and hollowing, ensuring better surface quality and durability in building projects.