Roof Waterproofing with Belzona

What is Roof Waterproofing?

Roof waterproofing is the process of applying a specialised coating to a roof to create an effective watertight seal that protects the working or living area below from water ingress.

The roof of your building is the first line of defence against the continuous bombardment from the elements. Usually, the highest and most exposed part of your building, roofs are expected to remain watertight and robust enough to withstand all that mother nature can throw at them. However, due to the constant exposure to the elements, damage to the roof is inevitable, leading to cracks, water leakage, seepage and costly repair bills.

Water leaking into your building can cause mould and mildew to form and grow on your walls. If your building contains any timber structures, these can be drastically affected by water, causing them to rot, which significantly weakens their structural properties. In addition, if water penetrates a building’s electrical system, this can cause a myriad of issues, from short circuits to total switchboard blowouts, not to mention the potential risk of electric shock to employees.

Prevention is always better than the cure; therefore, an effective roof waterproofing solution is vital to preventing water damage to your building and saves you the time and costs of replacing the whole roof.

Contributing Factors to Roof Damage

Rain is one of the major factors; heavy storms and monsoons in some parts of the world make roofs more susceptible to water-related damage due to the large volume of water falling in such a short space of time.

Heat damage occurs after the roof is exposed to direct sun rays for a prolonged amount of time; this exposure has a detrimental effect on the roof structure and can cause the roof to expand and crack, allowing for water leaks later.

Cold damage is caused by the freeze/thaw cycles during the winter months; freezing water in cracks and crevices on your roof can expand several times due to temperature fluctuations during the day and night. These continuous expansions increase the pressure on the roof, causing significant wear.

Poor maintenance can lead to cracks in the roof surface increasing over time; if the cracks are left untreated, they will quickly grow larger, causing the surface area to lose its overall strength and allow water to pass through.

Installed structures such as water tanks and mobile communication towers need to be installed professionally and frequently checked for any corrosion at their install points. Any corrosion to their fastening bolts could allow water to leak through the roof.

These factors can compromise all roofs, but flat roofs, in particular, can deteriorate extremely quickly. The lack of surface run-off causes this rapid deterioration as it produces a high quantity of surface water that can penetrate the substrate. Other areas susceptible to damage include joints and seams, flashings, gutters and glazing bars, as these are areas in which water can quickly accumulate.

Conventional Roof Repairs

There are many ways in which leaks are commonly fixed. One method is to replace the damaged material with the same material, a like for like repair. Unfortunately, using the same material to replace the damaged material leaves the roof surface subject to further damage. While this method may temporarily repair the leak, the level of protection achieved can be limited. As well as this, many original roof surfaces do not lend themselves to use for local repair. This method can also prove highly expensive, considering the costs required for the material replacement and the labour required for installation.

Other issues can further be identified when conventional repair techniques are used to rectify a leak. For example, common solutions use hot work, yet this can prove an unsafe, highly time-consuming, and disruptive repair method. Alternative repair materials can be used, but these can contain hazardous solvents that can create numerous Health and Safety implications and incur significant disruptions when used in public and commercial areas.

In many ways, these methods fall short of achieving a comprehensive repair that is cost-effective, non-intrusive, long-lasting and exceptional in terms of durability.

Roof Waterproofing with Belzona

Belzona has been providing roof waterproofing materials and liquid coating solutions since 1965; our solutions are widely used to repair and protect all types of roof problem areas, including joints, seams, glazing bars, skylights, and flashings, which are especially prone to deterioration and damage leading to water leaks.

Our low-odour roof coatings have outstanding waterproofing and weatherproofing capabilities and will ensure your roof stays protected for as long as 20 years or more.

Roof Waterproofing Application Areas with Belzona

A graphic showing all areas Belzona Roof Waterproofing can be applied

Belzona 3111 (Flexible Membrane)

Belzona manufactures a range of lightweight liquid-applied roof coatings such as Belzona 3111 (Flexible Membrane), which provides excellent roof waterproofing and weatherproofing properties, ensuring long-term protection from leaks, damage and deterioration.

Photo Belzona 3111 Roof Waterproofing Application
Close up off Belzona 3111 Application
Belzona 3111 Application on skylights

Used in conjunction with Belzona 9311 (Reinforcement Sheet), the system creates a durable weatherproofing and roof waterproofing membrane for almost all roof substrates and other structures. Thanks to its low odour, this water-based material can be applied at almost any location, including schools, hospitals, and public buildings. Belzona 3111 is certified by the British Board of Agrément (BBA) and approved by the Miami-Dade County.

The European Technical Approval ETA-05/0075, issued by the British Board of Agrément, indicated that the assumed working life of Belzona 3111 roofing system is 25 years.

 British Board of Agrément Logo

Belzona 3111 Technical Data

Belzona 3111 Roof Waterproofing Technical Data Table

Roof Coating and Protection with Belzona 3111

Belzona 3121 (MR7)

Emergency repairs such as sealing of leaks, damaged expansion joints and seams can be instantly completed using Belzona 3121 (MR7), which will bond strongly to most roof substrates and will cure even if fully immersed in water providing instant waterproofing.

Belzona 3121 Roof Waterproofing Application being used for emergency repair
Technician repairing roof expansion joint with Belzona 3121
Belzona 3121 Roof Waterproofing Application repairing a gutter.

Belzona 3121 is a lightweight seamless membrane system that will bond strongly to various substrates, including concrete, brick, copper, lead, cast iron, galvanised steel, asphalt, and stone. It is used in conjunction with Belzona 9331, a synthetic reinforcing sheet used to bridge roof contours and control film thickness.

Belzona 3121 Technical Data

Belzona 3121 Roof Waterproofing Technical Data Table

Belzona 3121 – Roof Repair System for Emergency Situations

Belzona 3131 (WG Membrane)

Designed for application in all weather conditions, Belzona 3131 (WG Membrane) is a cold-applied liquid coating that offers long-term repair and protection for all types of roofs.

The moisture-activated urethane roof coating, Belzona 3131 (WG Membrane), bonds to all types of roofing materials and will not be damaged by rain even immediately after application. In addition, the applied system incorporates a reinforcement sheet to allow easy control of the coating thickness during the application, and it adapts to roof movement due to its outstanding elasticity.

Belzona 3131 Roof Waterproofing Application on a large flat roof
Close up Belzona 3131 applied to roof guttering
Large scale Belzona 3131 Roof Waterproofing Application on a factory roof

The system provides long-term weatherproofing and waterproofing and offers excellent protection against infra-red and ultra-violet radiation and natural and industrial pollutants. It is impermeable to water but permeable to water vapour, allowing a moist roof to breathe.

Belzona 3131 Technical Data

Belzona 3131 Roof Waterproofing Technical Data Table

Belzona 3131 Application

Benefits of a Roof Waterproofing System

Roof Lifespan Increased

Applying a Belzona roof waterproofing membrane will significantly extend the life of the roofs of your buildings. Our protective membranes defend your roof from water ingress and reduce the damaging effects of extreme heat and light on your roof.

Structural Damage Prevented

Due to a leaking roof, water ingress can cause corrosion to the steel and wooden beams that support your building. In addition, concrete that is a porous material can also be affected by chemicals in the leaking water; deterioration of this concrete can be averted with effective roof waterproofing.

Reduced Health Risks

Water ingress into any building can lead to health issues for your employees, such as allergies or breathing difficulties, resulting from the formation and build-up of mould and mildew. A proactive approach to roof waterproofing will safeguard your employees from such health problems


A professionally installed roof waterproofing system is considerably more cost-effective over the long term when compared to the costs incurred for repeated repairs and, in extreme circumstances, a complete roof replacement. Adding waterproofing to your building also increases the structure’s integrity and commercial value.


Belzona’s liquid applied Polymeric Membranes contain outstanding waterproofing and weatherproofing properties, combine this with their excellent flexibility and high adhesion qualities, and you have the perfect system to ensure your roof will remain protected for the long term.

The low odour, cold-applied systems are installed with minimal disruption allowing for a rapid and safe installation across a multitude of locations and roof types.

Belzona Roof Waterproofing Case Studies

Interested in purchasing Belzona’s repair composites and protective coatings?

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