Reasons for hollowing and peeling of the exterior decorative layer
If the hollow drum issue is detected early and addressed proactively, safety hazards can be easily avoided. The main causes of hollow drum and peeling on the exterior decorative layer of a building can be summarized into the following four categories:
Insufficient bond strength between the base and facing layers.
② Defects in mortar thickness and structure.
③ Insufficient base levelness and the effect of temperature;
④ Natural external factors causing hollowing, water leakage, and peeling off.
External wall cladding hollow detection main technical methods
Based on the "Technical Code for Detecting Adhesion Defects in the External Wall Cladding of Buildings by Infrared Thermal Imaging Method": The detection of hollowing in the external wall cladding layer primarily uses infrared thermal imaging, supplemented by methods such as hammering, mortar tensile testing, and drone aerial photography.
Infrared thermal imaging
Principle of Infrared Thermal Imaging
The exterior walls of general buildings undergo cyclic temperature changes due to variations in temperature or solar radiation throughout the day or year. The surface temperature of the buildings varies due to the physical properties of specific wall materials, such as specific heat and thermal conductivity, as well as differences in surface morphology and condition, leading to variations in the temperature field distribution within the walls. Infrared thermography rapidly scans and detects the temperature field distribution of the building's exterior walls using an infrared thermal imager, representing the surface temperature field of the object in the form of a two-dimensional thermal image. Through comprehensive processing and analysis, it can determine the presence of defects. The advantage is that it can perform non-contact scanning of the exterior walls, quickly identifying infrared radiation anomalies in the wall finish, thereby rapidly locating areas of quality defects in the exterior wall finish.
02 Test Methods and Result Determination
Quickly scan and detect the temperature field distribution on the exterior walls of buildings using an infrared thermal imager, which presents the temperature field of the surface in a two-dimensional thermal image. Through comprehensive processing and analysis, determine if there are any defects. The characteristics reflected in the infrared image are: generally, in the absence of interference, the infrared photos of high-quality exterior walls show a relatively uniform temperature color, with no obvious areas of relative color difference. However, for exterior walls with quality defects (such as hollowing), the infrared photos typically exhibit distinct areas of color difference anomalies.
Mortar Pullout
On-site, wall mortar tensile tests are conducted at randomly selected locations on the building's exterior walls. The testing equipment includes tensile plates (100*100mm, thickness 8mm), tensile testers, and auxiliary tools (adhesives, cutting machines, etc.). The samples are cut according to the tensile plate size, with the cut going through the base layer but not exceeding 2mm in depth.
Drone Aerial Photography
On-site, drones are used to inspect the facades of buildings layer by layer from above, capturing aerial footage of wall damage and floor locations. The results of the aerial images are then analyzed.
Hammering method
Based on the infrared measurement results, a hammering method was employed to re-inspect the facade in areas of doubt, to determine the specific hollowed areas of the house.
