Supervising an Apprentice on a Multi-Unit Drainage Rough-In
A plumbing company has three crews working on a 12-unit townhouse development. The plumber-in-charge holds the licence and is on site Monday and Friday but spends Tuesday to Thursday on another project 40 km away. A second-year apprentice and a first-year apprentice are installing sanitary drainage and stormwater rough-in under the slab. On Wednesday the site supervisor reports that a 100 mm sewer line has been laid with a fall that looks flat and one junction has been glued without primer. The concrete pour is booked for Thursday morning. The licensed plumber is contactable by phone but not present. The builder wants the pour to proceed to avoid a crane booking fee of $2,800.
1. Assess the supervision arrangements against the plumber's on-site responsibilities and state what must happen before the Thursday pour.
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A licensed plumber remains responsible for supervising plumbing work carried out by apprentices, and supervision must be adequate for the competence of the workers and the risk of the task. Two apprentices, one in first year, laying under-slab drainage unsupervised for three days is not adequate supervision. The plumber must attend site before the pour, personally inspect the sewer grade, the junction preparation and all joints, and either rectify or direct rectification. The pour should not proceed until the drainage has been inspected and, where the work is notifiable, the required inspection has occurred. The builder's crane fee is a commercial pressure that does not override compliance. The plumber should also review the supervision model - for example, arranging a competent licensed person on site during rough-in or reducing the apprentice-only periods - and record the corrective actions. Allowing the pour would bury defective work and expose the licence holder to disciplinary consequences.
2. The apprentice says the fall 'looks fine' and the junction was glued without primer. Explain the technical and quality-control issues and how the plumber should document and correct them.
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Sanitary drainage must be laid at the minimum gradient required for the pipe size so that solids are carried and the drain self-cleans; 'looks fine' is not a measurement. The plumber should check the grade with a level or laser over a known run and compare it to the standard. Primer is required for solvent-welded PVC joints to ensure a sound bond; a joint glued without primer may leak or fail under test. The plumber should cut out and remake the affected junction, re-check the grade and re-test the line before the pour. Documentation should include photos before and after rectification, a written record of the inspection, the test result, and a note of the corrective action taken. This supports the quality-control obligations of the licence and gives the builder and certifier evidence that the buried work complies. It also creates a training record for the apprentices.