Direct answer
Sheet membranes are factory-calibrated rolls welded on site; liquids are applied coatings that cure into a continuous film. On Pakistani commercial work, PetroGrip APP/SBS covers most roof and basement planes where lap inspection and modifier type (APP vs SBS) are spec requirements. Polyurethane and polyurea from Petroseal address terraces with complex falls, industrial bunds, water tanks, and swimming pool structures where seamless coverage matters.
Imported multinationals and local contractors may push one technology exclusively. Petroseal publishes separate system pages so consultants can mix bitumen and liquids in one project with clear interface details.
Comparison table
| Factor | Sheet membrane (PetroGrip) | Liquid (PU / polyurea) |
|---|---|---|
| Thickness control | Roll gauge + lap overlap | DFT gauges, multiple coats |
| Large flat raft | Strong default | Requires strict QA on thickness |
| Complex geometry | Many laps, detail strips | Often faster seamless |
| UV exposure roof | APP cap + surfacing | PU topcoat systems where specified |
| Chemical immersion | Select grade carefully | Polyurea often specified for tanks |
| Manufacturing source | Petroseal Lahore rolls | Petroseal supplied coatings |
Combined systems
Basement field areas in SBS with liquid at pipe clusters is common. Roof APP cap sheet with polyurethane at odd-shaped plant plinths reduces lap count. Document the interface: liquid termination onto prepared membrane surface per method statement.
What to reject in tenders
- Unnamed liquid brush coat without DFT on basement raft
- Torch membrane without APP/SBS call on exposed roof
- Liquid applied over unsound or uncured concrete
- No inspection hold before tiles or backfill