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At RJ Evans we have a specialist mastic asphalt team which can carry out asphalt tanking works. Our highly-experienced asphalt tanking team covers all of London and the South of the United Kingdom. Each member of our team is fully accredited mastic asphalt specialists and covered with the appropriate qualifications and insurance.
Mastic asphalt tanking is a great way to waterproof structures which are below ground level. Mastic asphalt's great waterproofing qualities and proven track record over many decades make it a natural material for tanking. In fact, despite been used for many decades it still is largely unrivalled as a tanking system.
Asphalt tanking is a way of creating a seamless waterproofing lining to protect areas below ground level from moisture penetration by ground or sub-soil water1. Asphalt is one of the longest used materials for tanking systems, giving it a proven track record which hardly any other waterproofing membrane can match.
The purpose of tanking 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 formula2.
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 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 slab3 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.
• Mastic asphalt taking has a proven track record of success as an underground waterproofing membrane over many decades.
Mastic asphalt is renowned for it's fantastic waterproofing properties and is often referred to as 'The King Of Waterproofing', making asphalt tanking a natural choice to waterproof underground structures.
• Mastic Asphalt has a carbon zero rating.
• Mastic Asphalt is environmentally friendly as it is a totally recyclable material.
• 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.