Liquid waterproofing is an increasingly popular system for durable, cost-effective and seamless protection of flat roofs of any size, as well as areas of high foot traffic such as walkways, balconies, and terraces. With a lifespan of up to 25 years and often beyond this, it’s not difficult to see why liquid waterproofing systems are in high demand for all kinds of building and renovation projects.

This blog explores the benefits of liquid waterproofing, in particular PU (Polyurethane) and PMMA (Polymethyl Methacrylate) systems and the most suitable uses for each.

What are the main benefits of using liquid waterproofing?


Cold Application

Liquid systems such as PU and PMMA are known as ‘cold applied’, meaning they have flame-free installation, which gives them a distinct advantage over ‘hot’ waterproofing methods. This is particularly beneficial for use on sites where there are no hot works permitted and helps to reduce the safety risks involved in comparison to hot application methods.

Cold application is also ideal for use on sites with limited storage or difficulty getting a power source to the application area – there’s no cabling or noisy generators required.

Quick and Easy Process

The nature of cold-applied liquid systems means that they are very quick and easy to apply and can be used on a multitude of surfaces with full bonding to substrates and even to existing roofing membranes, in the instance of a repair.

The liquid form also allows for a much easier detailing process around vents and other penetrations, resulting in a beautifully seamless and aesthetically pleasing finish.

Low to No Odour

Cold-applied liquid waterproofing systems generally tend to have little to no odour which can be useful when considering applications in more sensitive areas such as hospitals, nurseries, care homes and other residential buildings.

Long-lasting and Trafficable

Liquid waterproofing systems are extremely versatile and can be used on a number of surfaces for an impermeable and hard-wearing finish, particularly on highly trafficable areas such as carparks and walkways, with anti-skid topcoats and colour selections available.

PU Systems (Polyurethane)

Why PU?

Polyurethane systems are one of the most popular types of liquid waterproofing with a long and successful record in the UK market due to the versatility of the product. The flexible nature of PU systems allows for a long-lasting finish with a reduced potential for cracks.

PU systems also provide excellent protection against UV radiation, heat and water ponding.

Suitable for:

  • Low to no odour settings
  • Pitched roofs
  • Flat roofs
  • Warm roofs
  • Green roofs
  • Metal roofs
  • Roofing repairs
  • Balconies and walkways
  • Complex detailing
  • New construction and refurbishment projects

Check out our Opti-Flex 20 PU waterproofing system here.

PMMA Systems (Polymethyl Methacrylate)


Why PMMA?

PMMA systems are most widely known for their rapid curing qualities – our OptiFlex-Rapid PMMA system cures in as little as 20 minutes (subject to weather conditions). This makes these systems ideal for sites where constant access is required, e.g., stairways and carparks.

Usually formulated with a minimum of 2 components (a resin and a catalyst/activator), PMMA systems are mixed on-site and cure rapidly, even at temperatures of around 0˚C.

Much like PU systems, PMMA systems are extremely hard-wearing and flexible, often with a lifespan of 25 years or more.

Suitable for:

  • Sites with limited timescales
  • Pitched roofs
  • Flat roofs
  • Warm roofs
  • Green roofs
  • Metal roofs
  • Roofing repairs
  • Balconies and walkways
  • Complex detailing
  • New construction and refurbishment projects


Check out our Opti-Flex Rapid PMMA waterproofing system here.

If you have any questions about our OptiFlex liquid waterproofing systems, please don’t hesitate to get in touch by calling: 01268 944054 or by emailing: info@optitec.group.