Case Study – Terrace Flat Roof Waterproofing Coating, Bournemouth
From failing roof to finished system
The Challenge
This residential flat roof terrace in Bournemouth had an existing asphalt roof covering that was starting to fail, with leaks forming around parapets, outlet junctions, and skylight upstands. The homeowner wanted a complete flat roof waterproofing upgrade that would offer long-term protection and allow for decking to be laid over the top as a usable terrace area.
Following inspection, the surface was found to be structurally sound but exhibiting signs of age-related wear, cracking, and bitumen bleed, which made it an ideal candidate for encapsulation using the GacoFlex S42 system.
Project file
Book a free survey and we’ll come back with a fixed price for your own roof.
The Solution — step by step
Surface Preparation
The surface was first cleaned and degreased, removing dust, moss, and contaminants using stiff brushing and detergent wash-down. Any larger holes or tears in the asphalt membrane were repaired using GacoPatch, a high-build silicone repair compound compatible with the S42 system.
Seam Sealing and Detailing
All junctions, laps, and critical areas were detailed using Gaco SF42 Seam Sealant, including around skylight upstands, parapet bases, outlets, and wall interfaces. This flexible silicone sealant reinforces the system at high-stress areas, ensuring there are no weak points before main coating begins.
Primer / Bleed Trap Application
With all seams sealed and surface preparation complete, a coat of GacoFlex BleedTrap was applied across the entire surface. The BleedTrap layer acts as a base coat and oil blocker, preventing any residual bitumen oils from migrating into the topcoat, ensuring a clean, stable foundation for the S42 silicone coating.
Main Coating Application
Once the primer was fully cured, two full coats of GacoFlex S42 silicone coating were roller-applied across the entire roof surface.
Each coat was applied in a crosshatch pattern to ensure even coverage and the required film build for a 20-year warranty.
The coating was taken up all upstands, parapet edges, and vertical terminations, creating a continuous, seamless waterproof membrane with outstanding UV and ponding-water resistance.
The Outcome
The project was completed within 2 working days, providing a bright, uniform, watertight finish ready for the customer to install decking over the top. The final system offers a long-term, low-maintenance waterproof barrier, guaranteed for 20 years under Gaco’s S42 system warranty.
Products used
Gaco SF42 Seam Sealant
View product →GacoPatch (Localised Repairs)
GacoFlex BleedTrap Base Coat
GacoFlex S42 Silicone Roof Coating (2 Coats)
View product →Flat Roof Waterproofing
Explore the service →More Duratite projects in the UK and Northern Ireland
Chiswick, London, England ResidentialCase Study: Residential Flat Roof Insulation & Waterproofing, Chiswick, London
Read the case study
Torquay, Devon, England ResidentialCase Study – Flat Roof Waterproofing Coating & Refurbishment, Torquay
Read the case study
Warrenpoint, Co. Down Industrial — Asbestos Roof EncapsulationAsbestos Roof Encapsulation — SAICA Warrenpoint
Read the case studyHave a similar flat roof waterproofing project?
Tell us about the building and the roof, send a few photos, and we’ll book a free survey and come back with a fixed price — the same process that delivered this project.
Prefer to talk it through?
Speak to a specialist about your project — no obligation, no hard sell.