Ⅰ.Cause Analysis

1.Substrate Issues

·Unchamfered Substrate: The absence of a rounded chamfer (arc transition) at internal/external corners creates stress concentration, making the coating prone to cracking.

·Preexisting Cracks in Substrate:Unrepaired cracks in the substrate at these corners can lead to coating failure and leakage along the crack path.

·Insufficient Substrate Strength: A loose, dusty, or friable substrate at the corners compromises coating adhesion.

2.Coating and Material Issues
·Insufficient Coating Flexibility: Standard rigid coatings cannot accommodate movement and stress at corners, resulting in cracking and leakage.

·Absence of Reinforcement Material：Failure to incorporate fiberglass mesh or a fabric reinforcement layer reduces tensile strength at these critical points.

·Improper Material Lapping: Inadequate overlapping or sealing of the coating at the corner junction creates a weak point.

3.Improper Workmanship
·Lack of an Additional Layer: Omitting a dedicated waterproof reinforcement layer (additional coat) at the internal/external corners.

·Uneven Application: Excessively thick application of coating material can lead to localized shrinkage cracks upon drying.

·Incorrect Construction Sequence: Failing to address corners first and applying the coating simultaneously with the main field can lead to poor coverage and thickness.

4.Other Factors
·Structural Movement: Building settlement or vibrations induce stress concentration at corners, causing the coating to crack.

·External Mechanical Damage: Subsequent construction activities, impact, or foot traffic can damage the coating at the corners.

Ⅱ.Solutions

1.For Minor/Small-Scale Leakage
Clean the affected area, cut a V-shaped groove along the corner, fill it with hydraulic cement, and then apply a waterproof coating reinforced with fiberglass mesh.

2.For Major/Large-Scale Leakage
Remove the existing coating in the leaking section. Prepare the substrate by creating a rounded chamfer (recommended radius ≥50mm), repair any cracks, and strengthen the substrate. Re-apply a flexible waterproof coating, incorporating a fiberglass mesh reinforcement layer.

Ⅲ.Preventive Measures

1.Substrate Preparation
·Internal/external corners must be rounded (recommended: using hydraulic cement to form an R-angle transition), ensuring the substrate is smooth and crack-free.

·Strengthen any loose areas of the substrate using a penetrating primer/bonding agent to enhance its integrity.

2.Reinforcement Layer Installation
·Before general application, apply 1-2 initial coats of waterproof coating specifically at the internal/external corners, immediately embedding an alkali-resistant fiberglass mesh or polyester fabric reinforcement strip (width ≥200mm).

·During the main field application, ensure the coating fully covers the reinforcement layer and extends at least 50mm beyond it on both sides.

3.Workmanship
·Prioritize corner areas, applying the coating in "multiple thin layers" to prevent material buildup.

·Apply each subsequent coat perpendicular to the previous one to ensure uniform, pinhole-free coverage.

·For flexible coatings (e.g., polyurethane, acrylic), allow each layer to become touch-dry before applying the next.

4.Environmental Control
·Avoid application in low temperatures (<5°C) or high humidity (>85% RH), as these conditions can impair proper film formation.

·Protect the finished coating from foot traffic or impact for at least 48 hours after application.

5.Material Selection
·Select high-elasticity, high-adhesion flexible waterproof coatings specifically for corner applications.

·Where necessary, use pre-formed waterproof sheet membranes to encapsulate corners, enhancing joint sealing.

Note: For areas subject to significant structural movement, consider additional reinforcement using waterstops or metal clamping strips.