1. Material Selection (the most common pitfall)
You must use an exterior-specific, high-density board: density generally ≥1.2 g/cm³ (higher required for curtain-wall / point-anchored systems), thickness usually 14–18 mm, manufactured to the JC/T 412 standard. Interior boards have higher water absorption and lower flexural strength — using them on an exterior wall will inevitably cause problems. Where possible, use boards from the same batch on one facade to avoid color variation (adjacent boards ΔE ≤ 2).
2. Substrate and Sub-framing (furring) System
Substrate: wall verticality/flatness deviation ≤5 mm per 2 m, free of dusting and hollowing, bond strength ≥0.4 MPa.
Sub-framing: main (vertical) rails at ≤800 mm spacing, secondary (horizontal) rails at ≤600 mm spacing (calculated from panel module and wind load); after installation, verticality ≤3 mm and levelness ≤2 mm.
Corrosion protection is the critical point: use hot-dip galvanized steel (zinc coating ≥80 μm) or aluminum alloy for the framing; use 304 stainless steel for hangers and screws (316 near the coast). Cut ends of the framing must be touched up with rust-inhibiting paint, or rust will run down and streak the panel face.
3. Panel Installation and Fixing
Panel joints: leave a 3–5 mm expansion joint between panels (may be widened for large panels or regions with high temperature variation); never butt panels tightly — thermal expansion will crack the boards.
Fixing: stainless-steel / galvanized self-tapping screws; screw heads countersunk 0.5–1 mm below the surface without breaking the coating; screw spacing ≤150 mm at board edges and ≤300 mm in the board field; no fewer than 4 anchor points per panel. Predrill holes near panel edges before driving screws to avoid stress concentration cracking; a torque-controlled drill is recommended to ensure consistent fastening force.
4. Joint Waterproofing (the deciding factor in whether it leaks)
Waterproofing relies on the system, not the panel itself: use the three-layer defense of "joint sealing + ventilated cavity + waterproof breathable membrane" (rain-screen / pressure-equalized cavity principle).
Sealant: must be a neutral silicone weatherproof sealant (with adequate movement capacity), backed with closed-cell foam backer rod (diameter 20–30% larger than the joint width); sealant depth ≥6 mm, full and void-free. Clean the joint before tooling and keep the fresh sealant dry for 24 hours.
Cross joints: the intersection of vertical and horizontal sealant runs needs dedicated reinforced sealing to prevent leaks at that point.
Waterproof breathable membrane: lap ≥100 mm horizontally and ≥150 mm vertically; seal every fastener puncture with the specified tape.
5. Detail Terminations (leaks almost always occur at these locations)
Bottom: the bottom edge of the panel should be ≥50 mm above the apron/ground to avoid standing water; open-joint systems should have drainage holes at the bottom.
Door/window openings: leave a 5–8 mm gap between the window frame and the panel, filled with sealant; give the sill ≥3% drainage slope; add flashing / rain-screen baffles around the opening.
Corners: prefer one-piece L-shaped panels or reinforced framing at outside corners; sealant must run continuously with no breaks at corners.
Top: terminate with flashing caps at parapets / eaves to prevent water from running behind the cladding.
6. Movement Joints and Construction Conditions
Provide a movement joint every 6–8 m, with sliding connectors across the joint, movement allowance reserved, and a stainless-steel expansion cover.
Avoid construction in rain and extreme temperatures; re-apply moisture protection to cut edges after site cutting; follow proper fall-protection measures for high-rise work.
7. Acceptance Reminders
Inspect the first row of panels immediately after installation (framing position, joint width, flatness, hanger fixity) before proceeding. If feasible, run a 15-minute hose water test to check for leaks; randomly remove one panel to verify membrane integrity and hanger condition.
