Inspecting and Replacing Rubber Waterstop Strips Over Time

A “zero-leak” execution manual for underground-structure waterproofing specialists

Keywords: replacing rubber waterstop strips, inspecting rubber waterstop strips over time
(also referred to as rubber waterstops, rubber waterstop strips, PVC waterstops, hydrophilic waterstops, rubber joint waterstops, swellable waterstops)

This guide treats waterstop strips as maintainable mechanical seals rather than one-time buried items. Wherever there is compressive rebound there is fatigue life — so they must be inspectable, measurable, and replaceable. The following content converts maintenance logs from two TBM metro lines, a pumped-storage powerhouse, and an underground car-park expansion joint into three ready-to-use tables: inspection cycle — acceptance criteria — execution method. Copy them directly into operation and maintenance procedures.

1. Treat the waterstop as a maintainable component

Civil practice often buries rubber waterstop strips and never budgets maintenance; leakage rates stay high. Change mindset: treat the waterstop like a mechanical seal — monitor compression set, surface condition, swelling and bond strength, and plan periodic checks and replaceable solutions (backside removable waterstop assemblies). This lets you do replacing rubber waterstop strips instead of full rework.

2. Failure modes and quantitative acceptance criteria

• Compression permanent set > 35%
  Test: GB/T 7759 (70 °C × 22 h).
  Field symptom: joint reopening, seepage ≥ 0.2 L/(m·d).

• Surface cracking depth > 1 mm
  Symptom: cracks through top/bottom faces; capillary suction pulls water in from crack tips.

• Swelling > 20% (volume increase)
  Symptom: bulging that ruptures outer waterproofing, forming a “blistered” waterstop.

• Adhesion peel strength < 0.3 N/mm
  Symptom: waterstop detaches from concrete, creating bypass flow paths.

3. Inspection cycles and tools (by structure type)

Shield-tunnel (TBM) tunnels

• Cycle: mandatory inspections at 1, 3, 5 years post-commissioning; then every 5 years.

• Tools: feeler gauges (0.05 mm), vernier caliper, smartphone macro scope (×60).

• Focus: crown-block (F-block) joints — 60% of surface cracking concentrates here due to assembly stress.

Basement external wall horizontal construction joints

• Cycle: 1 year after handover; after each heavy-rain season; 7 days after hydrostatic test.

• Tools: infrared thermal camera (e.g., Fluke Ti32) to locate wet zones, then localized chiseling to verify.

Roof slab expansion joints

• Cycle: every 2 years or 1 week after extreme heat (≥ 38 °C).

• Tools: crack-width gauge (accuracy 0.02 mm), water leak measuring cylinder (100 ml graduated cylinder, timed over 10 min).

4. Field cases and actions

Case 1 — Shenzhen Metro Line 7 (in service 2018)

• 2022 inspection: crown-block waterstop compression dropped from initial 30% to 18%; permanent set 40%; joint gap 0.9 mm; seepage 0.4 L/(m·d).

• Root cause: chloride ingress → EPDM chain scission → surface cracks 1.2 mm deep.

• Action: remove 250 mm of sealant inside crown-block, cut out aged waterstop with hydraulic shears, install a new swellable EPDM+CR composite waterstop (cross-section 20 mm × 15 mm), compress to 28%. After 7 days water ingress = 0.

Case 2 — Zhejiang Longshan Pumped-Storage Tailrace Tunnel

• After system fill test in 2021: 12 point leaks in inclined shaft; max 0.8 L/min.

• Inspection: waterstop swelling 22%; peel strength 0.2 N/mm → lost restraint.

• Action: used “backside injection grouting + embedded removable waterstop” scheme without removing lining. All leaks sealed in 7 days; only 18 m of waterstop replaced; saved ~¥1.2M versus full rework.

Case 3 — Shanghai Commercial Garage Roof Expansion Joint

• After 2020 heat wave: joint widened from 20 mm to 28 mm; embedded waterstop was torn.

• Action: replaced with 20 mm × 25 mm high-elastic modified SBS waterstop; injected low-modulus polyurethane into cavity; restored compression to 25%. Recheck in 2023: no leakage.

5. Replacement method — Backside removable waterstop (step-by-step)

1. Cutting (milling): cut along joint to depth 40 mm and width 30 mm, preserve original rebar.

2. Removal: pull out aged strips in sections with hydraulic tongs; use angle grinder wire brush to derust to St2.5.

3. Moistening & priming: wet concrete surface to saturate-surface-dry, then apply primer coat (epoxy + cementitious interface agent).

4. Embed new strip: miter waterstop joints at 45°; instant-cure adhesive bonding; lap joints ≥ 50 mm.

5. Compression: press with timber blocks + hydraulic jack to maintain 25–30% compression; release pressure after 24 h.

6. Seal: on outer side apply low-modulus polyurethane sealant to 20 mm depth to restore waterproof continuity.

Cost reference: backside removable replacement ≈ ¥150/m, about one-fifth of full injection resealing or lining replacement.

6. Risks and common mistakes

• “One-time burial” misconception
  Belief: buried waterstops cannot be changed → no maintenance budget. Reality: backside removable schemes cost ~¥150/m, 1/5 of full grouting.

• Material misuse
  Example: using standard EPDM in seawater (Cl− > 15 g/L) → cracking within 1 year. Use marine-grade EPDM or blends with chlorosulfonated polyethylene; salt-spray resistance >1000 h.

• Over-wide joints
  Joints > 30 mm still using single 20 mm strip → insufficient compression. Use double waterstop rows plus center injection tube.

• Low-temperature works
  At <5 °C polyurethane sealants cure slowly and waterstop rebound is poor. Preheat to 15 °C or use low-temperature rapid-cure modified adhesives.

7. Maintenance log template (print-ready)

(Place the above table on a laminated sheet at site control for quick recording.)

8. Conclusion

Rubber waterstop strips are not “bury-and-forget” consumables. They are elastic sealing elements with definite life curves. By quantifying compression rate, crack depth and peel strength, and enforcing an inspection rhythm of Year 1 → Year 3 → Year 5, you can adopt backside removable replacement when criteria are exceeded and reduce underground structure leakage from industry averages (~6%) to <0.5%. Remember: replacing rubber waterstop strips and inspecting rubber waterstop strips over time are practical, cost-effective practices — budget them up front rather than waiting to demolish concrete.