Clean and prime. Seal circumference with PU sealant and bandage with liquid membrane + geotextile. If active flow and top inaccessible, drill NRV grid and inject hydrophilic PU. Verify with water test.
LQ-JUNCTION
Summary
Leakage at junctions occurs where dissimilar materials meet or where penetrations interrupt continuity. Differential movement is the dominant failure driver.
Why Junctions Leak
Junctions are interfaces between dissimilar materials — concrete with PVC, metal with concrete, polycarbonate skylight with roofing sheet.
Because these materials expand and contract at different rates (differential thermal movement), rigid detailing fails, cracks open, and water easily finds a path.
1. Pipe Penetrations (Concrete + PVC/Metal Pipes)
- Failure: Cracking and debonding at the annular gap where pipe passes through RCC slab. Concrete shrinks/expands differently than PVC/metal, leaving micro gaps.
- Where you see it: Bathrooms, kitchens, water tanks, STPs.
- Solution:
- Pack annulus with polymer-modified non-shrink grout.
- Apply epoxy primer + flexible PU sealant/epoxy putty around pipe base.
- Reinforce with geotextile + liquid membrane at junction.
2. Skylight Terminations on Industrial Roofs
- Failure: Skylight sheets (polycarbonate) expand/contract faster than metal roofing, breaking sealants at the termination detail. Rainwater seeps inside.
- Where you see it: Industrial sheds, warehouses, PEB structures.
- Solution:
- Use high-movement silicone sealants or PU hybrid sealants with UV stability.
- Provide flashing overlaps with butyl tapes or preformed bands to absorb movement.
- Avoid rigid cementitious patches which will fail under thermal cycling.
Typical junctions
- Pipe penetrations through slabs/walls
- Skylight terminations on metal roofs
- Parapet-wall to slab, curb-to-deck, sleeve openings
Symptoms
- Local dripping during discharge (pipes) or during rains
- Wet rings around sleeves; stains at skylight edges
Probable causes
- No flexible seal/band allowing movement
- Rigid mortar repairs at flexible interfaces
- Inadequate priming/compatibility with PVC/metal
Solution paths
- Flexible sealant repair with proper primers
- Local reinforcement band (geotextile + liquid membrane)
- Injection grouting when active flow is present and top is inaccessible
Recommended technologies
- PU sealant with epoxy/PVC primer
- 2K PU or PU liquid membrane bandaging
- Hydrophilic PU injection grout for running leaks
Quick SOP
1) Clean and abrade substrate; solvent wipe PVC/metal; apply appropriate primer.
2) Seal circumference with PU sealant; tool to concave profile.
3) Bandage area with 2K PU/liquid membrane and geotextile; ensure overlap.
4) If active flow: drill NRV grid and inject hydrophilic PU; then bandage.
Acceptance criteria
- Water test around penetration; no damp ring after 24–48 hr
Video Masterclass
Masterclass: Junctional Leakages Solutions — Coming Soon
Disclaimer
Conix is an industry initiative & a neutral resource, compiled from industry references and best practices. It is not brand-specific. Always cross-check with project requirements and local codes before finalizing specifications.