We are regularly asked about the difference between cold applied waterproofing systems by clients. The confusion, and misunderstanding is very understandable, given that may of the systems appear almost identical in their finish and application method, however their performance and suitability varies hugely, and specifying inccorectly could have both significant long and short term cost implications.
Below we review the three most common cold applied “liquid” waterproofing systems, GRP, PU and PMMA systems.
GRP Roof Systems: GRP is a composite material made from a combination of glass fibers and polyester or vinyl ester resin. It is often referred to as fiberglass. The system is known for being durable, lightweight, and resistant to corrosion.
PU Cold Applied Liquid Roof Systems: Like both the others, PU systems are cold applied, meaning no heat or flame is required to install them. The polyurethane resin is poured and spread by rollers, or sprayed onto the surface, a reinforcing membrane is added – usually fibreglass – and it then cures at ambient temperatures. A second application is then added, which provides UV protection. No mixing or activation of a catalyst is typically needed. These systems form a seamless, monolithic membrane, which eliminates the potential for joints, seams, or overlaps that can sometimes be a source of leakage in other systems.
It is highly flexible and can adapt to the shape and movement of the roof, making it ideal for complex or irregular roof shapes.
PMMA Cold Applied Liquid Systems: PMMA (Polymethyl Methacrylate) roofing systems are a type of liquid-applied roofing solution that uses acrylic-based resins to create a durable, waterproof, and seamless roof membrane. PMMA is a high-performance polymer that is well-regarded for its speed of application, longevity, and UV resistance. It’s commonly used in commercial roof applications.
For roofing, the PMMA resin is mixed with hardeners or curing agents and then applied as a liquid. Once applied, it forms a seamless, elastic membrane that is highly resistant to weathering and UV radiation.
Application Process
GRP Roof Systems:
GRP systems are applied in layers. First, a resin is applied to the roof, followed by the application of glass fiber mats, which are then saturated with additional resin.
The system requires catalyst activation and typically uses a wet lay-up method, which involves working with resin and glass mats in situ.
After curing, the GRP membrane is tough, but it can sometimes require a topcoat for UV protection and aesthetics.
PU Cold Applied Liquid Roof Systems:
PU systems are cold applied, meaning no heat or flame is required to install them.
The polyurethane resin is poured or sprayed onto the surface, where it then cures at ambient temperatures. No mixing or activation of a catalyst is typically needed.
These systems form a seamless, monolithic membrane, which eliminates the potential for joints, seams, or overlaps that can sometimes be a source of leakage in other systems.
PMMA Systems:
Cold-Applied: PMMA roofing systems are typically cold-applied, which means they don’t require heat or flame to install. The resin is simply mixed with a hardener and applied directly to the surface.
Fast Curing: One of the standout features of PMMA roofing systems is their rapid curing time. PMMA can cure in as little as 30 minutes, allowing the roof to be back in service quickly after application. This makes it ideal for quick repairs or installations with minimal downtime.
Layered Application: The system generally involves the application of a primer, followed by a liquid resin layer, then a reinforcement fleece for added strength, and finally a topcoat for UV protection and additional durability.
Durability and Performance
GRP Roof Systems:
- GRP systems are resistant to UV rays, weathering, and corrosion, and they provide a tough, rigid surface once cured.
PU Cold Applied Liquid Roof Systems:
- PU Systems are usually highly resistant to UV radiation, water, and weathering. PU systems also provide flexibility, which helps prevent cracking, especially in areas that experience thermal movement.
- The system maintains flexibility after curing, which allows it to cope with the roof’s movements, expansion, and contraction.
- PU systems may require minimal maintenance, but the flexibility means the system is less prone to cracking or damage from roof movement.
PMMA System:
- PMMA roofs are highly resistant to the elements.
- The liquid-applied nature of the system means there are no joints, seams, or welds that could potentially leak. The system forms a completely seamless membrane, ensuring excellent waterproofing properties.
- While PMMA is a strong material, it also offers a level of flexibility once cured, which is important for roofs that experience movement due to temperature changes or settling.
- It provides good impact resistance and is suitable for foot traffic, making it a popular choice for both commercial and residential buildings with access to the roof.
Curing Time
GRP Roof Systems:- Curing is typically faster than PU systems, but it depends on ambient temperature and the curing agent used. A longer curing time is often required for deeper layers.
PU Cold Applied Liquid Roof Systems: – The curing time can be longer, depending on the temperature and humidity. Typically, PU systems cure in hours but can take longer for complete curing and are very dependent on external weather conditions.
PMMA Systems – Due to the catalysed nature of PMMA systems, these are fast curing systems, that can in many cases dry within 30 minutes and be ready to received a second coat within 2-4 hours.
Conclusion
GRP roof systems are generally lower cost, fast applicable systems that offer strength and durability. However, due to their rigid nature the are far less flexible than PU or PMMA systems, meaning that over large commercial roof areas they are more prone to cracking and damage on building than are more prone to thermal movement. As such, they are rarely specified or recommended for large commercial roof areas.
PU cold applied liquid roof systems are much more flexible and better suited to large commercial roof areas. Due to their slower curing time, they lend themselves to roofs where numerous complex details are present, however are much more reliant on suitable weather conditions than other systems, as such tending to incur greater labour costs during their installation. Over colder months, when temperatures fail to reach double digits, PU systems may take significantly longer to cure, resulting in slower project completion times and increases in preliminary costs.
PMMA Systems offer a greater deal of flexibility compared to GRP systems, and in turn lend themselves to large commercial roof areas. The catalysed nature of the system allows them to cure faster than PU systems and as such allows quicker application and more flexibility in weather conditions. However, in terms of material costs PMMA systems tend to come with higher material costs, albeit in some cases this can be offset against quicker installation costs.
In summary, when considering the most suitable system for commercial roof areas, PU and PMMA systems due to their flexibility will lend themselves more appropriately.
