Reasons for hollowing and peeling of the exterior decorative layer
If the hollow sound issue is detected early and addressed proactively, safety hazards can be easily avoided. The main causes of hollow sound and detachment in the exterior decorative layer of a building can be summarized into the following four categories:
Insufficient bonding strength between the base and decorative layers.
② Defects exist in mortar thickness and structure.
③ insufficient base levelness and temperature effects;
④ Natural external factors causing hollowing, water leakage, and peeling off.
Main techniques for detecting hollow sound in exterior wall facing
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 for auxiliary detection.
Infrared thermal imaging
01 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 employs an infrared thermal imager to rapidly scan and detect the temperature field distribution of the building's exterior walls, presenting the surface temperature field in the form of a two-dimensional thermal image. Through comprehensive processing and analysis, it can determine the presence of defects. Its advantage lies in the non-contact scanning of the exterior walls, enabling the rapid detection of abnormal infrared radiation on the wall finish, thereby quickly locating areas with quality issues in the exterior wall finish.
02 Testing Methods and Result Assessment
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, without 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 Pull Test
On-site, random positions on the exterior walls of the building are selected for the tensile test of the wall mortar. The testing equipment includes tensile plates (100*100mm, thickness 8mm), tensile tester, and auxiliary tools (adhesives, cutting machines, etc.). The specimens are cut according to the size of the tensile plates, with the cut going deep into the base layer but not exceeding 2mm.
Drone aerial photography
On-site, drones are used to inspect the exterior walls of buildings layer by layer from above, capturing aerial footage of wall damage and floor locations. The results of the aerial photography are then analyzed.
Pounding method
Based on the infrared measurement results, a hammering method was used to re-inspect the facade in areas of doubt, to determine the specific hollowed area of the house.
