Cracking of Prefabricated House Roof

The cracking of a prefabricated house roof may be caused by issues such as rapid shrinkage, improper steel bar placement, and problems with the splicing process of the prefabricated bottom formwork. The danger level of cracks needs to be evaluated based on their size, location, and changes, and different cracks have corresponding repair methods.

Causes of Cracking

• Rapid Shrinkage: After concrete is poured onto the roof, it requires curing during the setting period. If the weather is hot and water evaporates too quickly, the concrete sets too fast, preventing internal air bubbles from being squeezed out. Over time, the bursting of these air bubbles can lead to cracks.
• Improper Steel Bar Placement: Steel bars primarily serve a tensile function within concrete. Adding steel bars haphazardly can alter the overall tensile force, causing inconsistent shrinkage and setting, which in turn leads to cracks. For example, adding several large through-bars to already laid steel bars or installing electrical boxes for lights in the middle of the house can trigger such problems.
• Problems with the Splicing Process of the Prefabricated Bottom Formwork: When using the 3D steel bar truss floor panel prefabricated construction process, cracks may appear at the splicing locations of the prefabricated bottom formwork. This is because stress changes occur at the splices, and if the bonding strength between panels does not meet expectations, regular fine cracks can develop.

Evaluation of the Danger Level of Cracks

According to the 'Technical Guidelines for the Safety Inspection of Self-built House Structures', cracks in prefabricated panels exceeding 1 millimeter require vigilance, and cracks larger than 1 millimeter are considered dangerous. However, the location of the crack is also crucial. If it is a load-bearing crack, such as a horizontal crack that appears when the roof sags, even a crack as small as 0.8 millimeters should be noted. If a crack extends from the roof all the way to two-thirds of the height of the wall or is exactly on a load-bearing beam, the danger factor doubles. If a crack continues to lengthen and widen, even if it has not reached 1 millimeter, a professional organization should be consulted for inspection.

Repair Methods

• For cracks as thin as a hair, they can be directly sealed with glue.
• For medium-sized cracks, special adhesive should be injected, and it takes 72 hours to dry. During construction, problems can easily occur with panel joint treatment. When installing prefabricated panels, a 10 - 15 millimeter thick layer of mortar should be used.