Cover It Advanced GRP Waterproofing

What is Cover-it GRP?

Glass reinforced polyester (also called GRP or fibreglass) is a composite made from resin reinforced with glass fibre strands; it is seam-free and fully waterproof. Cover-it GRP enhances this proven technology with an easy-to-mix base resin, powder hardener, and UV-resistant top coat. When applied to OSB3 or similar decking, chopped-strand fibreglass mat is laminated into the wet resin, creating a continuous, joint-free surface. Because the system is cold-applied, there’s no need for heat tools, making installation safer and simpler. Cover-it is supplied as a complete kit – including base resin, top coat, catalyst, and reinforcement – perfect for contractors and confident DIYers alike.

How Cover-it GRP Works

• Base resin and chopped-strand mat: Resin is mixed with a powder hardener and rolled onto the roof deck. A 450 g/m² fibreglass mat is laid into the wet resin and consolidated.

• Top coat: Once cured, a durable, UV-resistant top coat provides the final waterproof finish.

• Trim profiles: GRP trims form neat edges at fascia, upstands, and outlets.

The Cover-it Application Guide recommends applying the system in dry conditions between 5 °C and 30 °C.
You can view the official guide here.

Resin coverage is typically around 1.2 kg/m² using 450 g/m² mat. Because the resin cures even if rain interrupts, installers can pause work without stripping back uncured material.

Key Benefits

• Rain-resistant application: Unlike standard fibreglass systems, Cover-it cures through even if installation is halted by a light shower.

• Flexible technology: The advanced formula makes the cured membrane more resistant to cracking and splitting.

• Easy repairs and alterations: Repairs can be made without grinding back the top coat—simply clean, abrade, and over-laminate.

• Superior adhesion: Excellent inter-coat and trim adhesion reduces the risk of delamination.

• Durable and long-lasting: Professionally installed GRP roofs can last 25–30 years or more, out-performing traditional felt roofs.

• Waterproof and seamless: The resin-bonded laminate has no joints, making leaks far less likely. Its smooth surface sheds standing water efficiently.

• Versatile and safe: GRP is lightweight and can be moulded around complex shapes. The cold-applied process avoids naked flames, improving safety.

• Low maintenance: Once installed, GRP roofs require minimal upkeep—just occasional cleaning.

• Value for money: Although GRP costs more upfront, its longevity and reliability make it a cost-effective flat-roofing solution. Typical

Typical Applications

• Extensions, garden rooms, and outbuildings: Creates a sleek, modern finish on home extensions and garden offices.

• Garages and porches: Long life and low maintenance make GRP ideal for detached garages and lean-tos.

• Dormer windows and roof terraces: Easily moulded around upstands and parapets for a neat, watertight seal.

• Balconies and walkways: Cover-it can include an anti-slip finish for safe foot traffic areas.

• Commercial and industrial roofs: Excellent resistance to UV, frost, and mild chemicals makes it ideal for light-commercial applications

Installation Considerations

While confident DIYers can handle smaller roofs, professional installation is recommended for the best results. Preparation involves removing existing coverings, ensuring the substrate is dry, and fixing OSB3 T&G decking. Resin and catalyst must be accurately measured; the Cover-it guide suggests a powder-hardener level of 2–4 % depending on temperature. Always work in dry weather between 5 °C and 30 °C, and refer to the guide for coverage rates and pot-life adjustments.

Cover-it GRP vs Other Flat Roofing Options

Compared with felt or bitumen membranes, GRP offers superior longevity, strength, and resistance to leaks. Felt roofs typically last 10–15 years and may blister or crack over time, while GRP roofs last 25–30 years or more. EPDM rubber membranes are quick to install but are not as rigid or puncture-resistant. Although GRP may have a higher initial cost, the long-term savings from reduced maintenance make it one of the most reliable flat roofing options available.
Learn more about flat roofing here.

FAQs – Cover-it GRP & Fibreglass Roofing

1. How long does a Cover-it GRP roof last?
When installed correctly, GRP roofs typically last 25–30 years or more. Cover-it’s advanced resin formula and superior adhesion help extend service life.

2. Is Cover-it GRP suitable for balconies or walkways?
Yes. Cover-it GRP is suitable for balconies and terraces when finished with an anti-slip coating for extra grip and wear resistance.

3. Can I install Cover-it over an existing roof?
Generally, the old covering should be removed. GRP requires a dry, structurally sound substrate, typically OSB3 T&G boards, to ensure proper bonding.

4. Do I need a professional installer?
GRP systems are straightforward but require careful mixing and timing. For large or complex roofs, we recommend using a qualified installer familiar with GRP systems.

5. What maintenance does a GRP roof need?
Very little—just occasional cleaning to remove leaves and debris. If minor damage occurs, repairs are simple: clean, abrade, and apply a new laminate layer.

Discover why contractors and homeowners across the UK trust Cover-it GRP for reliable, seamless flat-roof waterproofing.
Shop the full range here.
Contact our team for expert advice.

Want some hands-on training led by Cover-it specialists?
Take your roofing skills further with practical courses run by JJ Roofing’s Training Academy. Our expert-led sessions cover best practices for using GRP roofing systems, including full demonstrations of the Cover-it range. Check out our latest training courses here