Views: 31 Author: Site Editor Publish Time: 2025-08-18 Origin: Site
Cracking in the anti-crack mortar layer is a common yet critical issue in external wall insulation systems—especially for inorganic insulation mortar, which is more prone to shrinkage-related damage. Left unaddressed, these cracks reduce thermal insulation efficiency, compromise wall durability, and even lead to water infiltration. This article breaks down the key causes of cracking (focused on material and construction factors) and outlines actionable preventive measures to ensure long-term system performance.
Material quality and compatibility lay the foundation for anti-crack performance. Below are the most frequent material-driven issues:
Insulation boards with a density below 18 kg/m³ lack structural stability—they are prone to dry shrinkage, deformation, or damage from minor impacts. Over time, this instability transfers stress to the mortar layer, causing cracks.
Solution: Specify boards with a density of 18–22 kg/m³ (compliant with industry standards). Conduct on-site density tests (e.g., sampling and weighing) before installation to avoid subpar materials.
Insulation boards require approximately 60 days of natural curing to stabilize their shrinkage rate. Rushing installation (e.g., using boards cured for ≤7 days) leads to post-installation shrinkage: the board continues to contract after mortar application, concentrating stress at board seams and cracking the mortar.
Solution: Plan material procurement 2–3 months in advance to reserve full curing time. Label boards with production dates to track curing progress.
Exposed insulation boards degrade at a rate of 1–1.5 mm per year (due to UV radiation, moisture, and temperature cycles). Delaying mortar application after board installation weakens the bond interface between the board and mortar, increasing cracking risk.
Solution: Apply anti-crack mortar within 48 hours of insulation board installation. If exposure is unavoidable, cover boards with waterproof tarps to shield them from the elements.
A large gap in thermal conductivity between insulation boards and anti-crack mortar causes severe thermal stress. For example:
Expanded Polystyrene (EPS) boards: Thermal conductivity ≈ 0.042 W/(m·K)
Anti-crack mortar: Thermal conductivity ≈ 0.93 W/(m·K)
This 22x difference means the two materials expand and contract at drastically different rates (e.g., during sudden temperature drops from 50°C to 15°C in rain), creating stress that cracks the mortar.
Solution: Select material combinations with balanced thermal properties. For high-conductivity mortars, use insulation boards with slightly higher thermal conductivity (e.g., XPS boards) to narrow the gap.
Mismatched components—such as using an adhesive not designed for the insulation board, or anti-crack mortar with high strength but excessive shrinkage—can cause the board or mortar to crack.
Solution: Source "system-matched" materials (adhesive, board, fiberglass mesh, mortar) from a single certified supplier. Verify compatibility via factory test reports before use.
Even high-quality materials fail if construction practices are substandard. Key construction pitfalls include:
Uneven substrates: If the base wall’s flatness deviation exceeds 3 mm, the insulation board and mortar layer will bear uneven stress.
Contaminated surfaces: Residual loose dust, oil stains, or unrepaired voids weaken the bond between the base wall and insulation layer.
Standards require at least 40% adhesive coverage per insulation board. Inadequate coverage (e.g., spot bonding with <20% coverage) reduces load transfer, leading to localized stress and mortar cracking.
Incorrect depth: Anchors driven too shallow (not reaching the base wall’s solid layer) or too deep (damaging the insulation board) fail to restrain board movement.
Inadequate quantity: Using fewer anchors than required (e.g., <6 anchors per m² for high-rise buildings) leaves the system vulnerable to wind or thermal stress.
Missing diagonal mesh: Window corners and wall edges are high-stress areas—omitting 45° diagonal fiberglass mesh here creates easy cracking paths.
Narrow mesh overlaps: Mesh overlaps of <100 mm (instead of the required ≥100 mm) fail to distribute stress across the mortar layer.
To eliminate cracking, combine strict material control with standardized construction practices:
Certification verification: Ensure all materials meet national standards (e.g., China’s JG 149-2003 for insulation boards and JGJ 144-2019 for external insulation systems).
Pre-installation checks: Test board density, measure curing time, and inspect mesh alkali resistance (via pH tests) before on-site use.
System compatibility: Avoid mixing components from different suppliers—prioritize integrated material systems with proven compatibility.
Smooth the surface: Use mortar to level base walls, ensuring flatness deviation ≤3 mm.
Clean thoroughly: Remove dust, oil, and loose particles with a high-pressure water gun; repair holes with repair mortar.
Apply interface agent: Brush a layer of interface agent on the base wall to enhance adhesion between the wall and insulation layer.
Full-adhesion method: Use a 10 mm×10 mm notched trowel to apply adhesive, ensuring 100% coverage (avoid spot bonding).
Staggered seams: Install insulation boards with staggered joints (like bricklaying) to avoid continuous stress lines. Keep board seams ≥200 mm away from window corners or wall edges.
Mesh embedding: Embed alkali-resistant fiberglass mesh in anti-crack mortar, ensuring the mesh is centered (mortar thickness above and below ≤5 mm total).
Overlap and reinforcement: Maintain mesh overlaps ≥100 mm; use double-layer mesh for ground-floor walls, window corners, and other high-stress zones.
Avoid extreme conditions: Do not apply mortar when temperatures >35°C, <5°C, or during rain or wind >level 5.
Post-application protection: Cover fresh mortar with shading nets (in heat) or waterproof tarps (in rain) for 24 hours to control drying speed.
Cracking in anti-crack mortar is not inevitable—it is preventable through proactive material selection, strict quality checks, and adherence to construction standards. Success depends on collaboration: designers must specify compatible systems, suppliers must provide certified materials, and contractors must follow standardized processes. By prioritizing "prevention over repair," we ensure external wall insulation systems deliver long-term thermal efficiency and durability.
