Can I just coat over my old roof membrane?
Sometimes. An overlay can work if the existing membrane is well bonded, the substrate below is dry, the new product is compatible with the old one and the falls are adequate. It fails when it traps water, sits on a debonded or blistered membrane, or does not fix the details where the leak actually is. A moisture survey and adhesion checks should come before any decision to overlay.
From the RRD Field Guide, checked against the sources cited in Flat Roof and Wet-Area Waterproofing in Singapore: Membranes, Ponding, Leak Tracing and Repair. General information, not advice for your project.
The fuller picture
Most flat-roof and bathroom leaks in Singapore come from failed membrane details, not the open field: upturns, outlets, penetrations and laps. Diagnose before repairing, using a controlled flood (ponding) test, moisture mapping and inspection. The code of practice is SS 637:2018. In strata buildings the roof membrane is common property, so the MCST repairs it.
More questions on this topic
- How long should a waterproofing ponding test last?
- Which is better: torch-on, liquid or cementitious waterproofing?
- Who pays for a roof leak into a top-floor condo unit?
- What does a waterproofing warranty usually cover?
- Why does my roof leak only during some storms?
- Do I need BCA approval to redo roof waterproofing?