Jointing and Installation
This domain tests jointing methods by material, the correct sequence of installation, and pressure testing before concealment.
Core rules and concepts
- Threaded joints for GI, using PTFE tape or compound.
- Solvent cement for UPVC and CPVC: cut square, deburr, clean with primer, dry-fit and mark insertion depth, apply cement to pipe and socket, push with a quarter turn, hold briefly, wipe the bead, cure before testing.
- Rubber ring push-fit for SWR drainage; compression for copper and PEX; flanged for pumps, valves and tanks with a gasket; brazing or soldering for copper; caulking for cast iron.
- Sequence: mark and chase, fit sleeves where pipes cross walls, fix clamps, maintain gradients, keep joints out of walls, provide access to every valve, then test.
- Test supply lines at 1.5 times working pressure for one hour with no drop; test drainage with a water test or smoke test before closing up.
Worked example
Solvent cementing a 32 mm UPVC elbow. Cut square, ream, clean with primer, mark depth, apply an even coat of cement on pipe and socket, insert with a quarter turn, hold 15–30 seconds, wipe excess, and allow full cure before a pressure test. Reasoning: primer softens the surface, the quarter turn spreads cement evenly, and premature testing blows the joint apart.
Traps that cost marks
- Skipping the primer or using too much cement.
- Pressure testing immediately after jointing.
- Burying a joint inside a wall or under a floor.
- Running a long horizontal drain without a vent, so traps lose their seal.