A Question of Choice: Which Liquid Waterproofing to Use? (as featured in RCI Magazine)

We know that liquid roofing and waterproofing systems offer a highly durable solution for both new build applications and the refurbishment of existing roof, balcony and walkways. Yet, what isn’t as widely published is that there isn’t one single liquid technology suitable for every project.

Here, we provide an overview of the different liquid chemistries and why certain chemistries are best suited for different applications. These include polyurea technology, cold applied liquid bitumen, Thermoplastic Block Copolymers (SEBS), PMMA (Polymethyl Methacrylate), Polyurethane, GRP (Glass Reinforced Plastic) and Flexible Polyester.

Polyurea Technology
First developed 40 years ago, polyurea technology is now an advanced liquid coating system offering many advantages to the building owner and contractor.

Polyurea’s main, major benefit is its quick curing qualities – ideal in applications whereby area access cannot be restricted for many hours. It is often tack-free within 10 to 60 seconds after application and can be trafficked within the hour, returning an area to service quicker than other coatings – an attractive quality in the UK’s unpredictable climate.

Typical applications of polyurea includes roofing but is also often specified for podium decks, plus, applications on balconies, bridge coatings, waste water treatment plants, landscape and water containment, aquarium linings, water parks, and play grounds.

Polyurea systems provide excellent adhesion to substrates including concrete, cementitious screeds, metal, plywood, asphalt and bitumen sheets. Epoxy or polyurethane primers are normally used to seal the substrate and enhance the bond.

Polyurea is a two-component system which during installation can require specialist mixings and application apparatus, such as plural component spraying equipment which should only be used by trained operatives. Suppliers of specialist equipment are more easily accessible today, but there are also hand-applied systems that don’t need specialist mixing equipment if operatives prefer.

Polyurea technology can be used in any new build or refurbishment project as systems are often quick and easy to apply, durable and are UV stable. Polyurea is also solvent free and produces minimal odour – meaning it’s often a popular choice for projects on occupied or sensitive buildings such as schools or hospitals.

Cold-Applied Bitumen
Bitumen technology has been used as a waterproofing solution for centuries. First developed in the 1800’s when natural bitumen was combined with jute or straw to provide a waterproofing solution, modern day technology has developed this technology to what is now one of the most popular construction materials.

The coefficient of thermal expansion of bitumen is considerably greater than most popular construction materials such as concrete or steel, meaning once applied, it is less likely to crack. Bitumen is versatile, easy to apply and maintain, durable and multi-functional, and can be used in a reinforced membrane or adhesive.

Although five-year guarantees of bitumen-applied roofs were the norm in the 1970’s when it became extremely popular as a liquid waterproofing solution, there are examples of these systems that have remained in service, untouched, for more than 35 years. Now, rubber modified bitumen emulsions and solutions are being used commercially to provide cost effective, high performance waterproofing with a lifespan of 20 years or longer.

Bitumen has experienced many developments over time – the introduction of highly insulated structures meant systems needed to cope with greater extremes of temperature – hotter summers and colder winters resulted in higher levels of thermal expansion and contraction – thus, the introduction of rubber based polymers was developed into product formulations.
The use of foam insulation in a warm roof construction also meant greater puncture resistance was also required, and this was achieved by replacing the original jute reinforcement with polyester and the use of high performance carrier membranes.

Thermoplastic Block Copolymers (SEBS)
This technology was first developed more than 50 years ago and has seen many advancements during this time. SEBS polymers are used in the refurbishment and waterproofing of both metal and asbestos profiled sheets and as a waterproofing solution on flat roof substrates such as bitumen sheeting, asphalt, single ply plastics and concrete.

This technology produces an elastomeric roof coating that combines long lasting protection against water penetration and ponding water, to give an extended durability and service life. It has excellent water resistance qualities and is often specified for roofs which have a lot of standing water.

The elasticity within the product enables it to cope with the expansion and contraction that occurs in different substrates including bituminous, plastics, EPDM’s, metal, asbestos, timber and concrete.

SEBS is a single pack system, which is attractive to many contractors as there is minimal loss or wastage, and part-empty packs of product can be used on the next project without compromising the waterproofing performance.

During application of a SEBS system, certain substrates need priming to ensure adhesion of the base coat which includes the embedding of the reinforcement layer. As well as adding strength and puncture resistance to the system, this reinforcement ensures even and required film thickness is achieved. A final topcoat is applied to complete the system.

PMMA (Polymethyl Methacrylate)
PMMA was first developed in 1928 by chemists’ William Chalmers, Otto Röhm and Walter Bauer, and was brought to market in 1933 by the Rohm and Haas Company. Now widely used in the construction industry, the success of PMMA relies on its rapid curing qualities as it can dry in 30 – 40 minutes and in some cases even quicker if required, by using additional catalyst.

PMMA-based systems tend to have a minimum of two components, the first being the resin and the second being a catalyst or activator. Contractors will mix the components together on site, starting a chemical reaction creating heat which cures the product.

The solvent-free, cold-applied liquid resin cures rapidly even at temperatures around 0°C or lower, and is installed wet-on-wet. This means the polyester reinforcing fleece is first saturated with liquid resin, bonding the membrane to the substrate, with the surface layer then applied onto the bonding coat whilst still wet – therefore forming a single, seamless membrane of uniform thickness.

PMMA is durable, flexible, hard wearing and ideal for waterproofing projects whereby access to site is very limited and work must be completed extremely quickly. This includes communal walkways, stairways, car parks or balconies on occupied housing blocks where having the building empty or restricting access to homes for long periods of time is just not an option. On smaller roof areas, a one-day application may be possible as there is no need to wait for drying between coats.

Polyurethane systems are probably the most popular chemistry types with a long track record in the UK market, because they are seen as versatile materials that can be used in a multitude of applications. Established for more than 30 years, Polyurethanes can provide a cost-effective option for metal roofs, gutters, flat roofs of any size, warm roofs, green roofs as well as trafficked walkways, balconies and terraces – further cementing its versatile benefits.

Products are available as both single and twin pack, may use glass fibre matting or polyester fleece reinforcement; single (wet-on-wet) application or multi-layer applications; and can be reactive systems, moisture triggered or moisture cured. There are a wide variety of Polyurethane products on the market, some have an odour and some are odour free; ideal for use in sensitive areas such as nurseries, hospitals, schools causing little disruption to occupiers of the building.

The elastomeric nature of Polyurethane coatings allows high flexibility to mitigate movement in the underlying structure, reducing the occurrence of potential cracks. As with many liquid waterproofing systems, Polyurethanes also give inherently good chemical resistance and excellent durability against long term UV radiation, heat and water ponding.

Glass Reinforced Plastic
This technology is often referred to as GRP, glass fibre or fibreglass, and consists of a glass fibre reinforced polyester resin. It was first developed around the 1940s and thanks to its non-corrosive, high strength and excellent waterproofing properties, GRP was quickly adopted by the roofing industry from the 1950s.

GRP systems are predominantly used for domestic properties with small flat roofs, best suited of less than 100 m2. This is because the system always requires the application of a quality plywood or oriented strand board substrate – but can also be applied to other surfaces such as concrete with the use of primers if required. Contractors would typically use GRP for foot trafficked areas such as walkways or balconies, and is also quite popular within local authority frameworks as well as garage roofs, outhouses and housing extensions.

The installation of GRP includes preparing and laying the substrate to form a structurally sound deck. Then, preformed edge trims are fitted around the perimeter of the roof, at any significant junction or change in pitch. The waterproof laminate of a GRP system is applied onto the deck, made up of roofing resin combined with a catalyst which is used to saturate a reinforcement mat – typically a chopped strand mat (CSM) material. Once the laminate has cured, a coloured topcoat which is mixed with a catalyst is applied over the surface using a brush or soft roller.

As with any liquid waterproofing solution, one key consideration for contractors before specifying a GRP system is always checking the manufacturer has third party accreditation. This is especially apparent for GRP systems as there are a number of new manufacturers on the market which may not have the appropriate certifications.

Flexible Polyester
This technology consists of an unsaturated polyester resin reinforced with either fibreglass mat or polyester fleece. Flexible Polyester is very fast curing which allows for quick walk-on times.

These systems can be applied to a wide range substrates and are equally suited to refurbishment or new build. Various colours and finishes can be incorporated with Flexible Polyester to suit the needs of the client, and to its tough finish, Flexible Polyester can be used for balconies as well as roofs.

The polyester resin incorporated within the system must be specially formulated to provide a high degree of flexibility and elasticity combined with fire performance. This technology can be used on all sizes of roofing projects and because of its component qualities, it is quick and easy to apply.

What to Specify?
It goes without saying, no matter which liquid waterproofing technology is specified, quality systems that are fully accredited will offer a durable, UV-stable, quick, easy and sound waterproofing solution. Liquid systems should also have appropriate third party accreditation such as BBA Certification and/or BDA Agrement (Kiwa).

For more information and advice on different liquid chemistries, please contact us.