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UKFR - ROOFING AND INSULATION SPECIALISTS
GRP and liquid rubber are two of the most popular waterproofing systems for flat roofs. While they both have seamless finishes and are both excellent choices for complex roof layouts, such as those with skylights, outlets, or unusual shapes, they are installed in very different ways.
In this blog, we’ll break down the differences between GRP and liquid rubber to help you make an informed decision.
GRP and liquid roofs share many of the same characteristics, only really differing in the way they are installed and how much they cost.
| GRP | Liquid Roofing |
|---|---|
| ✅ Creates a seamless, watertight seal | ✅ Creates a seamless, watertight seal |
| ✅ Can be walked on | ✅ Can be walked on |
| ✅ Highly versatile | ✅ Highly versatile |
| ✅ Lightweight | ✅ Lightweight |
| ✅ Highly durable | ✅ Highly durable |
| ✅ 15 and 25 years lifespan | ✅ 15 and 25 years lifespan |
| ❌ Expensive compared to simpler flat roof systems | ❌ Expensive compared to simpler flat roof systems |
| ❌ Not DIY-friendly – recommend using a professional | ❌ Not DIY-friendly – recommend using a professional |
GRP stands for glass reinforced plastic (commonly known as fibreglass), and it provides a fully watertight finish by combining resin with reinforcing matting. It’s incredibly malleable and once cured, is completely seamless, making it especially useful for complex layouts with intricate detailing, pipes or skylights.
Liquid rubber is a fully bonded, liquid-applied coating that can be used on most decking surfaces straight from the tin. Once cured, it forms a seamless, rubber-like, elastomeric waterproof membrane.
Despite the name “liquid rubber”, it isn’t actually made from EPDM rubber. The system is similar, as it forms what is like a single-ply membrane similar to EPDM, but one that is formed perfectly to the roof space.
GRP and liquid roofs are both highly malleable flat roof systems that can be formed to any required shape during installation, and once cured, create a fully seamless finish. This means they are great on complex roof layouts where you might have roof pipes or skylights, as they can be easily moulded around features without leaving any gaps where water can enter.
GRP and liquid rubber are incredibly lightweight and thin compared to traditional roofing materials, weighing at least 10 times less than code 8 lead and felt. This reduces the stress placed on the joist and overall roof structure.
Once fully cured, the roofs typically have a thickness of around 1-2mm and weigh between 1.5-2.5kg per sq.m (liquid roofs weigh slightly less, between 1.5kg to 2kg per sq.m, but this depends on the system you install).
GRP and liquid rubber both form a watertight, hard, rigid surface that supports foot traffic and is 100% watertight, becoming impenetrable against all weather conditions, including snow, ice, wind, rain, and subsequent physical impacts like hail or falling debris.
They’re incredibly flexible, adjusting to building movements and thermal changes all year round without showing any signs of cracking. They’re also highly resistant to UV, performing well in both hot and cold climates, making them less susceptible to cracks and blisters over time.
The majority of GRP and liquid roofs have a lifespan between 20 and 25 years, but this will depend on the amount of foot traffic and whether any damage is left unrepaired. If damage does occur, it should be repaired as soon as possible. See below for our product recommendations.
The biggest difference between GRP and liquid rubber is how they’re installed.
GRP
A GRP system works by melting the matting down in the resin to create a solid layer of waterproofing, which is then covered with a top coat to add UV protection. The matting typically requires agitation to ensure it breaks down properly.
There are three thicknesses of matting: 225g, 450g and 600g. Different thicknesses require different tools to break them down.
During installation, the surface must be completely free from pinholes; otherwise, they will become permanent once the surface cures.
Liquid Rubber
A liquid system uses a 225g matting as a reinforcement layer. Unlike the GRP system, where the matting dissolves in the resin, in a liquid system, the matting stays whole and only needs to be dampened and fully encapsulated within the liquid coating.
The liquid system is applied using a 65-70% base layer, followed by the matting gently rolled in, and then the remaining 30-35% added on top.
It’s important not to apply too much pressure to the matting as it can lead to two main problems:
Problem 1 – There can be too much material sitting above the matting. This leads to a skin forming around the material and not setting below, resulting in big bubbles forming on the surface. This is similar to paint when you put too much on. If this happens, it needs to be cleaned off and applied fresh again.
Problem 2 – Pinholes can form. Similar to GRP roofs, pin holes can form on liquid roofs as a result of trapped air from excessive movement of the liquid. When the liquid settles, the pinholes pop, making them visible in the finished surface. This is bad as it can let water in, leading to dampness and rot within the building structure.
GRP and liquid roofs are both considered premium flat roof options and will cost more compared to simpler systems like EPDM.
How much does GRP cost?
The cost depends entirely on the system and matting you choose. For example, RES-TEC Flexitec 2020 can range between £360 to over £2,000, whereas RES-TEC GRP 1010 can cost anywhere from £160 to over £1,100.
It also depends on the matting you choose; if you only require light roof access, then you would only need the 450g/600g matting and a basic top coat. However, if you anticipate a lot of foot traffic, you would need the more flexible 225g matting and an anti-slip grit top coat.
Find out exactly how much your roof will cost with our GRP Roofing Calculator.
How much does liquid roofing cost?
Just like GRP, the cost of a liquid roof depends entirely on your deck type and the required coverage, starting at £350 to £1500 for a complete kit.
Find out exactly how much your roof will cost with our liquid roof calculator.
At UKFR Roofing & Insulation, we’re committed to helping you find the best option for your project. As a family-run business with more than 50 years of experience in flat roofing, we’ve earned the trust of customers nationwide, with over 200 positive reviews from satisfied clients across the UK.
Get in touch today either via WhatsApp or call on 0800 054 8324, or send us an email to [email protected], we will be happy to assist.
