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Asphalt tanking refers to the application of mastic asphalt as a protective waterproofing membrane within underground structures, basements, or retaining walls to prevent water ingress and seepage. This specialised asphalt material is typically used to create a continuous waterproof lining which effectively seals off below-ground spaces from groundwater or moisture penetration. Mastic asphalt tanking is particularly suitable for environments where water resistance and durability are critical, such as in basements, tunnels, and other subterranean constructions. The application process involves heating and melting the mastic asphalt, which is then carefully applied as a hot liquid or semi-solid coating to form a seamless and resilient waterproofing layer, providing long-term protection against water damage and dampness in below-grade structures.
Mastic asphalt tanking is a specialised waterproofing technique used to protect below-ground structures, such as basements, cellars, and foundations, from water ingress and dampness. This method involves applying mastic asphalt, a durable and impermeable material, to the interior surfaces of walls and floors that are susceptible to moisture penetration. Mastic asphalt's unique composition, which includes a blend of the natural material bitumen, fine aggregates, and mineral fillers, enables it to form a seamless, monolithic layer that effectively seals the structure against water.
The process of tanking with mastic asphalt requires meticulous preparation of the substrate to ensure optimal adhesion and performance of the waterproofing layer. Once applied, the mastic asphalt cures to create a thick, elastic membrane that can accommodate slight movements of the building without cracking, thereby maintaining its waterproof integrity over time.
One of the key advantages of mastic asphalt tanking is its exceptional longevity and resistance to the corrosive effects of groundwater and soil chemicals. Additionally, its versatility allows it to be applied in various thicknesses, catering to different levels of water exposure and structural demands. Mastic asphalt tanking is renowned for its reliability in permanently waterproofing below-ground spaces, providing a dry, usable area free from the threats of water damage and damp-related issues.
Mastic asphalt tanking is recognised as a superior solution for waterproofing underground structures, combining high-performance waterproofing with environmental sustainability. Its exceptional properties not only offer robust protection against moisture ingress but also ensure the longevity and integrity of the structures it safeguards. With a proven track record spanning decades, mastic asphalt stands out for its flexibility, durability, and seamless application. These benefits, coupled with its carbon zero rating and recyclability, underscore mastic asphalt tanking as an ideal choice for environmentally conscious and effective underground waterproofing.
Mastic asphalt is renowned for its outstanding waterproofing capabilities often referred to as “The King Of Waterproofing”, making it the go-to choice for shielding underground structures from water ingress. Its dense, impermeable nature ensures underground moisture penetration does not penetrate the structure it protects. This keeps basements, tunnels, and foundations dry and secure. This material is particularly effective in areas prone to high water tables or where structures are directly exposed to groundwater.
Over the years, mastic asphalt has been consistently chosen for its reliable performance in waterproofing applications across the globe. Its long history of use in a variety of settings—from historic building renovations to modern infrastructure projects—demonstrates its effectiveness and the trust professionals place in this material.
Mastic asphalt's robust composition allows it to withstand the harsh conditions often found in underground environments, including exposure to aggressive soil chemicals and constant dampness. This resilience translates into a waterproofing solution that can last for decades without significant deterioration, reducing the need for frequent repairs or replacement.
Unlike more rigid materials that may crack or break under structural stress, mastic asphalt maintains its integrity through temperature fluctuations and building movements. This flexibility is crucial for an underground waterproofing membrane. This allows it to perform even as the structure it protects undergoes natural settlement or expansion.
Mastic asphalt's carbon zero rating highlights its role in sustainable construction practices. This certification reflects the minimal environmental impact of its production and application, aligning with the growing demand for green building materials that contribute to the reduction of carbon emissions.
The fact that mastic asphalt is fully recyclable further cements its status as an environmentally friendly waterproofing option. At the end of its life, mastic asphalt can be melted down and reused, minimising waste and promoting a circular economy within the construction industry.
The seamless application of mastic asphalt creates a monolithic waterproof layer that lacks joints or seams, which are often the weakest points in a waterproofing system. This continuous coverage ensures that there are no paths for water to enter, providing superior protection against leaks and dampness.
Mastic asphalt is highly resistant to the corrosive effects of soil chemicals and can also withstand root penetration, which is a common issue for underground waterproofing systems. This resistance ensures that the waterproofing integrity of the structure remains uncompromised, safeguarding it against both chemical degradation and physical damage from plant growth.
The purpose of mastic asphalt tanking systems is to prevent the penetration of ground or subsoil water. A basement consistently receives pressure from ground water. The degree of pressure exerted will depend upon the maximum water table level and how deep the basement goes beneath the water level. When planning to tank a basement it is best to assume the head of the ground water is developed from ground level all the way down to the deepest point of the basement. The reason for this is to allow for seasonal fluctuations in the water table.
The water pressure increases as you go deeper below the water level. To calculate the water pressure, you can use the following formula.
kN/sqm = 9.8 x metres below the water level
The pressure is exerted equally in all directions. Factors such as the slop of the surface on which the pressure exerts does not make any difference.
There are two methods available when it comes to mastic asphalt tanking. They are internal tanking and external tanking. As the name suggests internal tanking means applying the mastic asphalt waterproofing inside the structure and external tanking means applying the waterproofing outside the structure.
The decision over whether to use internal or external tanking for basement waterproofing will come down upon the specific conditions for the structure you want to tank. If conditions permit it is better to use external tanking. The reason for this is that ground water pushes the mastic asphalt lining into the structure. Whereas with internal tanking the force of the ground water pushes the mastic asphalt away from the structure.
When applying mastic asphalt to the external walls of a basement, the concrete base must extend at least 150mm beyond the outer face of the basement wall. The horizontal coat of asphalt is laid on the base concrete in 3 coats. These 3 coats must cover full area of the slab and come to a nominal thickness of 30mm.
Immediately after the asphalt is laid a sand and cement screed at least 50mm thick must by laid to protect the mastic asphalt against any damage from subsequent works. When this sand and cement screed is laid, it is important to take great care to ensure the mastic asphalt coating is not adversely affected.
The next step is to lay a loading coat of concrete over the sand and cement screed. The concrete applied must be of a sufficient strength to resist the maximum anticipated water pressure. No other work can be carried out until this loading coat of concrete has been put in place.
The loading concrete does not need to be applied over the minimum 150mm wide ‘pick up’ but the 50mm protective sand and cement screed must be laid on to building paper over the mastic asphalt ‘pick-up’ to prevent the asphalt surface becoming contaminated.
The basement walls are erected on top of the loading slab concrete. Next the protective screed and building paper is removed from the mastic asphalt ‘pick-up’ and the external face of these walls receive three coats of mastic asphalt to a thickness of 20mm.
At the junction between the vertical asphalt on the external wall and the mastic asphalt ‘pick-up’ a two-coat angle filet must be applied. When this angle fillet is created, it is imperative to ensure the ‘pick-up’ is completely free of contamination. The reason for this is to guarantee complete fusion between the asphalt ‘pick-up’ and the external wall.
Next a protective wall should be built against the external vertical mastic asphalt tanking membrane. A 40mm gap should be left between the protective wall and the mastic asphalt which must be filled solid with mortar, course by course as the work is carried out (this 40mm gap is essential to achieve a sound tanking system). The reason for this is to protect the mastic asphalt membrane from the effects of solar heating and any damage during the backfilling operation or any future excavation works.
If the internal tanking method is going to be used, the concrete base and structural walls should be completed prior to any mastic asphalt being applied. For a sound waterproofing membrane, the asphalt work should be completed in a continuous fashion to avoid any contamination from other sources.
Once the horizontal mastic asphalt coats and the bottom bay of the vertical mastic asphalt have been applied they must be joined with an angle fillet to create a watertight finish and to prevent any moisture penetration. Like with external tanking a 50mm protective screed of sand and cement should now be applied over the top of the horizontal coat of mastic asphalt once it is completed. It is preferable to have the protective screed in place before finishing the vertical of the asphalt wall.
Next, the structural concrete slab should be laid. And then the loading walls should be erected. It is imperative both the structural concrete slab and the loading walls can withstand the maximum anticipated water pressure.
Pumping During The Mastic Asphalt Tanking Process
When the asphalt tanking process is underway it is essential the ground water table is kept below the level of the base concrete. To do this pumping must be continually provided until the loading slab and concrete walls or brickwork mortar has been hardened. The main contractor should ensure there is backup in case of any problem occurring with the main pumping mechanism, this should not be the responsibility of the team carrying out the asphalt tanking.
Backfilling During The Mastic Asphalt Tanking Process
There should be no backfilling until all the tanking and loading has been completed.
Design Of The Concrete Base For Mastic Asphalt Tanking
The concrete slab which the asphalt tanking is applied to must be designed to ensure it can withstand any superimposed loads and prevent any movement which could cause cracking of the mastic asphalt. This includes concrete loading slabs, plant equipment, machinery and protective screed.
The concrete slab like any substrate which is to receive mastic asphalt should be as dry as possible, have a level surface, be free from dust, dirt and grease. And have no holes.
It is important that there is complete continuity between the mastic asphalt and the damp proof course to prevent any water ingress at the high level. The material used for the damp proof course must be compatible with mastic asphalt in terms of composition and manner of application.
• We have our own Asphalt Mixer this means a flame free laying of the mastic asphalt. Better consistency in the asphalt mixture meaning a more efficient installation process with a better overall finish.
• At R J Evans we have a vastly experienced asphalt team. We have operatives with more than 40 years’ experience.
• We provide a range of FREE quotations and solutions for all projects.
• Insurance Backed Guarantees.
• Excellent Customer Support throughout project.
• Rated 5 out of 5 from our previous customers.
If you would like a quotation or any information on mastic asphalt tanking please get in touch with us or call us now on 01277 375 511.
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