Case Study – Flat Roof Waterproofing Coating & Refurbishment, Torquay
From failing roof to finished system
The Challenge
This commercial flat roof in Torquay had been suffering from ongoing leaks and standing water due to failed seams and overlaps between the existing bitumen asphalt felt sheets. The roof surface had degraded over time, allowing water to track beneath the felt layers and saturate the underlying structure.
The client required a durable waterproofing upgrade that could be applied directly over the existing substrate — eliminating the need for a full strip and replacement. Following inspection, the roof deck was confirmed to be structurally sound, making it ideal for encapsulation using the GacoFlex S42 Silicone Roof Coating System.
Project file
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The Solution — step by step
Surface Preparation
The project began with a thorough cleaning and degreasing of the roof using GacoWash, a specialist biocidal treatment designed to remove moss, algae, surface grime, and oil contaminants.
All areas of trapped moisture were opened up and allowed to dry out fully before repairs were made. The surface was then inspected for cracks, delamination, or weak bonding between the bitumen felt layers, which were cut out and reinstated where necessary to ensure a uniform, sound substrate for coating.
Seam Sealing and Detailing
Once preparation was complete, all seams, joints, penetrations, and junctions were sealed using Gaco SF42 Seam Sealant. This flexible silicone sealant was applied to all critical points, including parapet bases, upstands, service penetrations, turrets, and perimeter terminations.
The SF42 detailing ensured that all potential ingress points were fully reinforced, eliminating the weak joints that had previously allowed water to penetrate between felt sheets.
Primer / BleedTrap Application
Following the seam sealing stage, the entire roof was primed using GacoFlex A4271 BleedTrap Base Coat. This layer acts as a primer and oil-blocking barrier, preventing bituminous bleed-through and stabilising the surface prior to silicone application.
The A4271 BleedTrap also promotes superior adhesion between the existing asphalt felt and the S42 topcoat, ensuring long-term compatibility and performance.
Main Coating Application
Once the primer had cured, two full coats of GacoFlex S42 Silicone Roof Coating were roller-applied across the entire roof area, including all detailing at upstands, parapets, turrets, and penetrations.
Each coat was applied in a crosshatch pattern to achieve even film build and total coverage. The result was a seamless, high-performance waterproof membrane with excellent resistance to ponding water, UV degradation, and thermal expansion — providing 20 years of certified protection.
The Outcome
The project was completed over 7 working days, allowing adequate drying time for cleaned and repaired sections, and staged curing of each coat.
The final result was a bright, uniform, watertight finish that eliminated all signs of previous leakage and standing water. The client was extremely pleased with the transformation, gaining a cost-effective, long-life flat roof waterproofing system installed without disruption to the building’s operation.
Products used
GacoWash (Roof Cleaning and Degreasing Treatment)
Gaco SF42 Seam Sealant
View product →GacoFlex A4271 BleedTrap Base Coat
GacoFlex S42 Silicone Roof Coating (2 Coats)
View product →Flat Roof Waterproofing
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