When cracks appear in a floor slab, simply repairing them is usually not enough. The key is to first determine the cause, type, and severity of the cracks, then develop a targeted treatment plan. Skipping diagnosis and jumping straight to repairs can mask underlying structural issues, leading to recurring cracks and even safety hazards. The following explains the core logic, treatment steps, and common misconceptions:

First, clarify: Crack type determines whether repairs are appropriate.

Floor cracks aren't a single issue. It's important to first distinguish between structural and non-structural cracks, as the treatment logic for each is completely different:

2. Correct Treatment Steps: First "Diagnosis," Then "Treatment"

Regardless of the type of crack, the "diagnosis first, then treatment" process should be followed to avoid blind repairs.

 Step 1: Preliminary Determination of the Crack Nature (Owners Can Conduct a Preliminary Investigation on Their Own)

Observe the Form:

Structural Cracks: These are often diagonal, crisscrossing, or extend along floor supports (such as walls or beams). The crack width may increase over time (mark the ends of the crack with a marker and observe after 1-2 months to see if they lengthen or widen).

Non-structural Cracks: These are often straight, short cracks concentrated on the floor surface, typically ≤0.3mm wide, and show no significant expansion.

Observe Accompanying Symptoms:

If cracks appear on the wall or floor near the crack (such as 45° cracks in wall corners), or if doors and windows are deformed and unable to close, it is likely a structural problem (abnormal stress on the foundation or floor).

If cracks are limited to a localized area on the floor surface with no other abnormalities, it is likely non-structural.

Step 2: Professional Inspection (Critical! Especially if Structural Issues Are Suspected)

If the initial diagnosis suggests possible structural cracks, or cracks ≥0.5mm wide and showing signs of leakage/expansion, it is essential to consult a qualified building inspection agency (such as a third-party agency approved by the local Housing and Urban-Rural Development Bureau) for an accurate diagnosis using the following methods:

• Rebound testing of concrete strength;

• Rebar detector to check if the number and spacing of rebar in the floor slab meet design requirements;

• Settlement monitoring (continuously monitoring for 1-3 months to see if the building is still settling);

• Crack depth testing (using an ultrasonic device to determine if the crack penetrates the floor slab).

Step 3: Targeted Treatment (Situation-Specific)

Non-structural Cracks (Shallow, Non-Expansive)

Repairs are recommended as the primary approach, but waterproofing is essential to prevent water seepage from affecting the lower level. The steps are as follows:

Crack Cleaning: Use a utility knife or brush to remove dust and debris from the cracks, ensuring they are clean.

Filling with Repair Material:

• Cracks <0.3mm: Use epoxy resin slurry (highly permeable) to seal the cracks.

• Cracks 0.3-5mm: Use polymer cement mortar (flexible and shrink-resistant) to fill and smooth the surface.

Additional Waterproofing (Optional): If the crack is in a humid area such as a bathroom or kitchen, apply a waterproofing membrane or paint after repair.

Structural cracks (deep, extended, and impacting load-bearing) require "repair first, then reinforcement." Do not simply repair cracks:

Crack repair: After reinforcement, seal the cracks with epoxy resin slurry.

Structural reinforcement: Select reinforcement methods based on test results. Common methods include:

• Bonding steel plates/carbon fiber cloth to the bottom of the slab (to enhance load-bearing capacity);

• Rebar reinforcement (drilling holes on both sides of the crack to insert rebar to increase the tensile strength of the slab);

• Foundation treatment (if caused by settlement, foundation reinforcement is required first, such as grouting and anchoring).

Follow-up monitoring: Observe for 1-6 months after reinforcement to confirm that the cracks have not expanded.

The core contradiction of floor cracks is not "whether to repair or not", but "why they crack" - non-structural cracks can only be repaired (with good waterproofing), while structural cracks must be repaired first and then reinforced.