Exterior wall insulation issues–Cracked plaster layer

Cracked plaster layer

Exterior wall insulation plaster layer is composed of plaster mortar and reinforced mesh. Plaster mortar is divided into bottom layer mortar and surface layer mortar. It is understood that when constructing the surface layer, first apply the bottom mortar on the surface of the installed external insulation board. Add reinforcing mesh, lightly apply the reinforcing mesh into the bottom mortar, and then apply the surface mortar on top. The thickness must not be less than 3 mm, and the texture must be exposed but not the mesh.
Plastering mortar, also known as anti-crack mortar or anti-crack mortar, plays a key role in the entire external insulation system. Create a reliable reinforced protective layer for exterior insulation panels. The cracked plaster layer cannot solve the problems of thermal insulation, heat insulation, wind pressure resistance, fire prevention, freeze-thaw resistance, waterproofing, weather resistance, flame retardant, breathability, cracking and other problems of external insulation.
reason:

1. Material factors.

The density of insulation boards for exterior wall insulation should be 18~22kg/m3. Some construction units will use inferior insulation boards of less than 18kg/m3 as good ones. Insufficient density can easily lead to cracking of the plastering mortar layer. The natural shrinkage time of the insulation board is as long as 60 days in the natural environment.
Due to factors such as capital turnover and cost control of production companies, insulation boards that have been aged for less than seven days are already on the wall. The result is that the insulation board continues to shrink after being installed on the wall. And the plastering mortar layer adhered to the insulation board is pulled apart.

2. Construction technology.

The flatness of the base surface is too large, and the use of adhesive thickness, multi-layer boards, surface grinding and leveling and other adjustment methods will lead to defects in the quality of the insulation. Dust, particles and other substances on the surface of the base layer that hinder the adhesion are not treated at the interface.
The bonding area of the insulation board is too small, does not meet the specifications. And cannot meet the quality requirements of the bonding area. When constructing a rice-surface mortar layer under exposure to the sun or high temperature. The surface layer will lose water too quickly, resulting in cracks.

3. Temperature difference changes.

Thermal conductivity of the two layers of expanded polystyrene board and anti-crack mortar is different. Thermal conductivity of expanded polystyrene board is 0.042W/(m·K). The thermal conductivity of anti-cracking mortar is 0.93W/(m·K). The thermal conductivity differs by a factor of 22.
When the sun shines directly on the surface of the plaster mortar in summer, the surface temperature of the plaster mortar can reach 50~70℃. In case of sudden rainfall, the temperature of the mortar surface will drop to about 15℃. And the temperature difference can reach 35~55℃. This temperature difference change is affected by the day and night temperature difference and seasonal temperature. The resulting deformation of the plastered mortar layer is large and prone to cracks.
Landcel HPMC for EIFS