Pipe Materials, Components, Jointing and Bedding
Match the material to the duty
Common NZ drainage materials include uPVC (solvent-cement or rubber-ring jointed, the default for building drains and sewer laterals), PE/HDPE (butt-fused or electrofused, good for long runs, rising mains and ground movement), concrete (AS/NZS 4058, large mains and stormwater), vitrified clay (chemically resistant), cast iron (acoustic and above-ground fire-rated situations), and copper and PP for particular above-ground and specialist uses. Each has its own jointing method, bedding class, deflection limits and handling rules.
Jointing failures are the most common defect. Solvent cementing requires the correct cement for the material, cleaning and priming, correct application, a quarter-turn on assembly and adequate cure time before testing or backfilling - cure is slower in cold weather. Rubber-ring joints need a clean socket, lubricant, correct insertion depth and the socket facing upstream. Electrofusion needs a clean, dry, correctly scraped pipe and the right fusion cycle.
Bedding provides uniform support: a trimmed trench bottom, a nominated granular bed, proper haunching under the pipe, then overlay and backfill. Flexible pipes rely on side support to resist deflection (typically limited to around 5%); rigid pipes rely on the bedding class and must not be point-loaded on rock. Components - bends (including rest bends), junctions, gullies, traps, inspection openings, boundary kits, backflow devices and sleeves through footings - must be the correct type and pressure class for their location.
Traps
Mixing solvent cements across material types. Testing before joints have cured. Using a rubber-ring socket facing downstream. Bedding a rigid pipe on hard rock without a cushion layer.
Rule of thumb: trench width for a flexible pipe is generally the pipe outside diameter plus about 300 mm, giving working room to haunch properly.