Inspection and Repair of Blistering on a Single-Ply Membrane
A 5-year-old single-ply TPO membrane roof (500 m²) on a distribution centre has developed numerous blisters, some up to 300 mm in diameter. The membrane is mechanically attached and has a 10-year warranty. The building owner reports that the blisters appeared after a period of heavy rain followed by hot weather. A recent inspection revealed that some blisters have ruptured, and water is entering the insulation. The roof has a 1:100 fall to outlets, but ponding is observed in several areas. The membrane manufacturer's technical representative has visited and suggested that the blisters may be due to moisture in the substrate or inadequate adhesion. The client wants a permanent repair.
1. What are the possible causes of the blistering, and what tests would you perform to diagnose the issue?
Read the worked answer
Possible causes: (1) Moisture in the substrate: Trapped moisture from construction or leaks vaporises in hot weather, creating pressure under the membrane. (2) Inadequate adhesion: If the membrane is mechanically attached, blisters may occur where the membrane is not fully bonded or where fasteners are insufficient. (3) Ponding water: Areas of ponding allow water to be absorbed, increasing risk. (4) Manufacturing defect: Though less likely, a defect in the membrane could contribute. (5) Installation error: e.g., not allowing for thermal movement, or contaminating the surface before bonding. Tests: (1) Moisture survey: Use non-invasive moisture meter or infrared thermography to map wet areas. (2) Core sampling: Cut cores to inspect the insulation and substrate for moisture; measure moisture content with a calibrated meter. (3) Adhesion test: Perform pull tests on the membrane to assess bond strength. (4) Fastener check: Inspect fasteners for tightness and spacing. (5) Visual inspection: Check for ruptures and water entry points. (6) Thermal imaging: To identify wet insulation. (7) Review installation records: Check if the membrane was installed in damp conditions.
2. Outline a repair strategy that addresses both the symptoms and the root cause, and explain how you would ensure the repair is warrantable.
Read the worked answer
Repair strategy: (1) Address root cause: If moisture is present, remove wet insulation and allow the deck to dry. If ponding is due to inadequate falls, consider adding tapered insulation or adjusting outlets. (2) Repair blisters: Cut out blistered membrane, dry the area, and patch with new TPO membrane using hot-air welding. Ensure the patch extends at least 50 mm beyond the blister. (3) Reinforce attachment: If fasteners are insufficient, add additional fasteners or use a fully adhered system in problem areas. (4) Replace wet insulation: Remove and replace any wet insulation to prevent future blistering. (5) Improve drainage: Clear outlets and ensure falls are correct. (6) Quality control: Use a qualified installer, follow manufacturer's instructions, and document all repairs with photos. (7) Warranty: Obtain written approval from the manufacturer for the repair method before proceeding. Use manufacturer-approved materials and applicators. After repair, arrange for a manufacturer's inspection to validate the warranty. Keep records of moisture readings and repairs. (8) Monitoring: Schedule follow-up inspections to ensure no new blisters form.