Water Retention Requirements for Plastering Mortar
1. Plastering Mortar for High-Absorption Substrates
High-absorption substrates are typically represented by aerated concrete, and also include various lightweight partition boards, blocks, and similar materials. These substrates are characterized by rapid water uptake and prolonged absorption duration.
For plastering mortars applied to such substrates, the following requirements should be met:
Hydroxypropyl Methylcellulose (HPMC) water retention: ≥ 93%
Mortar water retention: ≥ 88%
2. Plastering Mortar for Low-Absorption Substrates
Low-absorption substrates are typically represented by cast-in-place concrete, and also include polystyrene boards used in external wall insulation systems. These materials exhibit relatively low water absorption capacity.
For plastering mortars applied to such substrates, the following requirements should be met:
HPMC water retention: ≥ 93%
Mortar water retention: ≥ 88%
3. Thin-Layer Plastering Mortar
Thin-layer plastering refers to applications where the thickness of a single layer ranges from 3 mm to 8 mm. Due to the reduced thickness, moisture tends to evaporate rapidly, which may negatively affect workability and final strength.
Therefore, higher water retention is required:
Mortar water retention: ≥ 99%
4. Thick-Layer Plastering Mortar
Thick-layer plastering refers to applications where the thickness of a single layer ranges from 8 mm to 20 mm. Due to the increased thickness, moisture loss is slower, resulting in comparatively lower water retention requirements.
Recommended values are as follows:
HPMC water retention: ≥ 93%
Mortar water retention: ≥ 88%
5. Water-Resistant Putty
Water-resistant putty is an ultra-thin plastering material, typically applied at a thickness of 1 mm to 2 mm. Such materials require very high water retention to ensure adequate workability and bonding strength.
General requirements:
Putty water retention: ≥ 99%
Exterior wall putty should have higher water retention than interior wall putty
