How to Repair a Leaking Flat Roof
A practical guide to liquid roof repair systems — when to use liquid rubber, EPDM or SprayGrade, and how to choose the right product for your project.
Quick Answer: How Do You Fix a Leaking Flat Roof?
For most residential flat roof repairs, liquid rubber systems such as HBS200 are the fastest and most practical solution. Clean the surface, apply liquid rubber to leak areas and details, then coat the full roof. For full roof replacement, EPDM systems are the industry standard. For large commercial roofs, spray-applied systems like SprayGrade cover approximately 600m² per day under suitable conditions.
In short: liquid rubber repairs, EPDM replaces, SprayGrade covers at scale.
Choosing the Right System
Liquid Rubber (HBS200)
Best for repairs, detailing and smaller areas.
- Leaking flat roofs
- Gutter sealing
- Joints and penetrations
- Small-medium areas
EPDM Roofing
Best for full flat roof replacement.
- Full roof replacement
- New builds
- Extensions and garages
- Long-term membrane system
SprayGrade
Best for large commercial roofs.
- Warehouses and factories
- approximately 600m² per day under suitable conditions
- Commercial refurbishment
- Asbestos encapsulation
Simple rule: use liquid rubber for repairs and details, EPDM for full replacement, SprayGrade for commercial scale.
When Liquid Rubber Is the Right Choice
There's a specific leak or damp area
Gutters, joints or outlets are failing
Roof penetrations need sealing
The existing structure is still sound
You want a quick, low-disruption repair
Budget is limited and full replacement is overkill
When to consider EPDM instead
The entire roof surface has failed
It's a new build or full extension
The felt is beyond repair
You need a complete long-term membrane replacement rather than a local repair
Step-by-Step: How to Repair a Flat Roof with Liquid Rubber
Assess the Leak
Identify where water is entering. Check gutters, joints, penetrations and upstands as well as the main membrane surface. These are the most common failure points.
Clean the Surface
Remove dirt, moss, algae and loose material. The surface must be clean and dry before application. Any loose or flaking coating must be removed.
Seal Joints and Details First
Apply liquid rubber HBS200 to all joints, seams, penetrations and edges. This creates the watertight base layer before coating the main roof area.
Apply Liquid Rubber Coating
Brush or roller-apply HBS200 across the full affected area. Apply two coats for best performance. Coverage is approximately 5–8m² per kg.
Allow to Cure
Touch dry within hours. Full cure within 24 hours depending on temperature and humidity. Do not apply in very cold or wet conditions.
Quick Answers
Does liquid rubber stop leaks?
Yes. Liquid rubber creates a seamless, flexible membrane that seals leaks in flat roofs, gutters and roof details.
How long does liquid rubber take to cure?
Liquid rubber typically becomes touch dry within hours and fully cures within 24 hours depending on temperature and humidity conditions.
Is liquid rubber better than felt?
For repairs and detailing, yes. For full roof replacement, EPDM rubber systems are the more durable and longer-term solution.
Can liquid rubber be applied over existing coatings?
Yes. Liquid rubber bonds to felt, concrete, metal and other substrates, avoiding the need for full removal.
Liquid Rubber Supply Across the North West
Forti Nova supplies Liquid Rubber HBS200 from the Blackburn depot in 1kg, 5kg and 20kg packs. Collection and delivery timing are confirmed per order against current availability and destination.
EPDM Flat Roofing
Full flat roof covering system. Long-term membrane system. Used for new builds and full replacements.
View EPDM RoofingSprayGrade Commercial
High-output spray system for large commercial roof refurbishment. approximately 600m² per day under suitable conditions.
View SprayGradeForti Nova supplies EPDM, Liquid Rubber and SprayGrade systems across the North West — serving Blackburn, Preston, Manchester, Bolton, Wigan and Warrington from our Blackburn depot.
Need Help with a Flat Roof Repair?
Call 01254 433987 for product advice, coverage calculations and current collection or delivery timing. Forti Nova supplies liquid rubber, EPDM and commercial roofing systems.
01254 433987Need help choosing the right system?
Call our team or use our guided project enquiry — we'll recommend the right system based on your roof type, size and project requirements.