First-Time-Right Waterproofing: CONQUAS Lessons for Wet Areas, Roof Edges and External Walls

First-time-right is cheaper than rectification. A wet-area defect that goes through CONQUAS sampling costs the project a re-test, a re-membrane, a re-tile and a re-inspection. The pattern of defects under CONQUAS is well documented — the lessons are widely applicable, not just on assessed projects.

Wet area — the three repeat defects

• Wall upturn too low or absent above shower zone
• Pipe collar missing or only flat-applied membrane around the stub
• Floor trap upstand not encapsulated, membrane stops at slab level

All three are detailing failures, not membrane failures. They are designed out at the method statement stage with a typical wet-area detail drawing approved before site work starts.

Roof edge — flashing and upstand

The roof slab membrane stops cleanly at the parapet upstand if the haunch is properly formed and the membrane is dressed up and over. The repeat defect is membrane terminated below the flashing line, with a sealant strip relied on to bridge the gap. Sealant alone is a five-year solution at best.

External wall — joint sealant and crack repair

On a coated external wall, the repeat defect is loss of sealant adhesion at movement joints and uncontrolled crack propagation. The coating is sound; the joint or the crack is not. The fix is a properly sized joint with the right backing rod and a movement-tolerant sealant, with PU injection at structural cracks before the area-wide coating.

Documentation discipline

CONQUAS rewards documentation almost as much as workmanship. A wet area that passes the ponding test but has no signed record gets marked down. The simple fix: a one-page record per wet area, photos at each step, signed by the supervisor.

Material lessons

Material substitution at site, without re-checking the data sheet for compatibility, is a recurring source of failure. A switch from a polymer-modified cementitious to a "similar" product can change adhesion, elongation and the spread rate. Substitutions are documented and approved, not slipped in.