Quality Assurance and Quality Control
QA is not QC
Quality assurance is the system: the written quality plan, procedures, inspection and test plans, submittal review, mock-ups, and audits that make outcomes predictable. Quality control is the execution: the actual inspection, testing, and measurement that verifies the work meets the standard. Questions love this distinction. Know the three-phase inspection process - preparatory, initial, and follow-up - and inspection and test plans with hold points (work stops until released) and witness points (notification required). Understand first-work and mock-up approval, and the special inspection and testing requirements of IBC Chapter 17 for concrete, structural welding, high-strength bolting, and fireproofing. Know who pays for tests: the contractor for its own quality verification, the owner for separate testing, and the responsible party for retests of failed work.
Nonconformance and closeout
Understand nonconformance reports and dispositions - rework, repair, use-as-is with approval, reject - plus root cause analysis and the cost-of-quality categories: prevention, appraisal, and failure (internal and external). Closeout ties quality to documentation: punch lists, commissioning, training, warranties, and as-built records.
Traps
Confusing QA with QC is the most common single error. Another is assuming an owner's or architect's observation substitutes for contractor quality control. When a failed test is re-tested, the question usually turns on who pays and whether work may proceed in the interim.
Rule of thumb
For any work that will be covered, tested, or hidden: submittal approved, preparatory meeting held, initial inspection on first work, follow-up through completion, then cover. Catching a defect before cover-up costs a fraction of catching it after.