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Asphalt roofing is the process of using mastic asphalt as a waterproofing membrane to protect the roof of a building. Mastic asphalt is a highly durable, waterproofing material made from a mixture of finely graded aggregates and bitumen, a form of asphalt. This blend creates a dense, impervious membrane which is spread in molten form over the roof surface. Upon cooling, it forms a hard, seamless layer. Renowned for its longevity. Asphalt roofing is ideal for flat or slightly sloped roofs, offering excellent protection against water and weathering. It is low-maintenance and can be effectively used in various settings, including commercial, industrial, and residential buildings.
Mastic asphalt roofing is a highly durable waterproofing solution commonly used on flat or low-pitched roofs. It consists of a mixture of asphalt, finely ground limestone aggregate, and mineral fillers, which is heated and then poured or spread over the roof surface in layers to create a seamless, impermeable membrane. This type of roofing is known for its exceptional longevity, often lasting over 50 years with proper maintenance, and its ability to provide superior protection against water penetration, making it an ideal choice for protecting buildings from the elements.
The flexibility of mastic asphalt allows it to adapt to temperature changes and building movements without cracking, ensuring a continuous waterproof barrier. Its application process is flame-free, enhancing safety during installation and reducing the risk of fire. Additionally, mastic asphalt roofing is environmentally friendly, as it is carbon zero rated and fully recyclable, aligning with sustainable building practices.
Mastic asphalt's versatility also extends to its ability to be applied to a variety of substrates and its compatibility with complex roof shapes and details, such as around chimneys and vents. Furthermore, its smooth finish can be left exposed or covered with reflective coatings or green roof systems, offering both functional and aesthetic benefits. This combination of durability, waterproofing excellence, and environmental sustainability makes mastic asphalt roofing a preferred choice for commercial and residential roofing projects alike.
Mastic asphalt offers a range of compelling benefits that make it an outstanding choice for roofing solutions across various types of construction projects. Asphalt has exceptional waterproofing abilities, combined with its environmental sustainability and versatility in application, set it apart from other materials. Below, we delve into the specific advantages that underscore why mastic asphalt is a preferred option for those seeking durable, eco-friendly, and adaptable roofing systems, enhanced by the expertise of skilled craftsmen and the latest technological advancements.
Mastic asphalt is renowned for its unparalleled waterproofing qualities, offering a robust barrier against moisture and water ingress. Its dense, impermeable nature ensures that water cannot penetrate the surface, safeguarding the building from potential water damage, leaks, and the detrimental effects of dampness. This level of protection is critical for extending the lifespan of structures and maintaining the integrity of the building envelope.
Mastic asphalt stands out as an eco-conscious roofing solution, boasting a carbon zero rating that underscores its minimal environmental impact. Its recyclability further enhances its green credentials, allowing for the material to be reused and reducing the need for new resources. This commitment to sustainability makes mastic asphalt an ideal choice for projects looking to adhere to environmental standards and reduce their carbon footprint.
The adaptability of mastic asphalt across a wide range of applications highlights its versatility. From waterproofing car parks and flooring to tanking and balcony installations, its effectiveness in various settings showcases the material's broad utility. This versatility ensures that mastic asphalt can meet the specific waterproofing and protective needs of different structures, making it a go-to choice for diverse construction projects.
Mastic asphalt offers the significant advantage of a flame-free installation process when using an asphalt mixer. This method eliminates the risks associated with open flames on the construction site, enhancing safety for workers and the surrounding area. Additionally, the flame-free approach contributes to a more efficient and safer installation process, reducing the likelihood of fire-related incidents.
One of the unique strengths of mastic asphalt is its capability to mold and conform to tight, awkward spaces, ensuring comprehensive coverage and effective waterproofing even in complex architectural details. This flexibility allows for seamless integration around obstacles such as piping and upstands, providing a continuous waterproofing layer that leaves no gaps or vulnerabilities.
The ability to customise mastic asphalt with the addition of aggregates, like 30% grit for added traction or hardness, tailors the material to the specific requirements of a project. This customisation enhances the safety and durability of surfaces, particularly in high-traffic areas or service decks, where additional resistance to wear and slip prevention are crucial.
The installation of mastic asphalt roofing is carried out by highly skilled craftsmen known as spreaders, who are required to complete a rigorous minimum 2-year NVQ. This extensive training ensures a high level of expertise and reliability, guaranteeing that each asphalt roofing project is executed with precision and care, contributing to the overall quality and performance of the finished roof.
Recent technological innovations have revolutionised the preparation and application process for mastic asphalt roofing. These advancements significantly reduce the waiting time for screed curing before laying the asphalt, from traditionally up to seven days to almost immediate application. This improvement not only speeds up project timelines but also introduces integrated drainage solutions, eliminating the need for core venting and enhancing the overall functionality of the roofing system.
These benefits underscore the superiority of mastic asphalt as a waterproofing solution, combining durability, eco-friendliness, versatility, and safety, all backed by the expertise of skilled craftsmen and the latest in technological innovations.
Solar reflective paint is highly recommended for asphalt roofing systems which use roofing grade asphalt. It plays a crucial role in reflecting sunlight away from the roof surface, thereby reducing heat absorption and lowering the overall temperature of the building. This reflective capability not only enhances the energy efficiency of a building by minimising the need for air conditioning during warmer months but also extends the lifespan of the roof by protecting it against the deteriorating effects of UV radiation. Additionally, solar reflective paint adds an aesthetically pleasing finish to the roofing system, typically applied in a light grey shade at the completion of the roofing project.
However, it's important to note the distinction between roofing grade asphalt and recreational duty asphalt in this context. Recreational duty asphalt, designed for heavier traffic and more abrasive wear, incorporates extra grit and is more hard-wearing than its roofing grade counterpart. Due to its robust composition, recreational duty asphalt is less prone to slumping, and substrates protected by this material do not typically require solar reflective paint for additional protection. In contrast, substrates protected with roofing grade asphalt will benefit from the application of solar reflective paint, not only for its energy efficiency and protective qualities but also to compensate for the material's relative vulnerability to slumping and UV damage. This differentiation underscores the importance of selecting the appropriate type of asphalt and protective coatings based on the specific requirements and expected usage of the roofing system.
Mastic asphalt roofing specifications can include two or three layers. These specifications may consist of different types of asphalt being combined. An example of this would be in a car park where roofing grade asphalt is used in unison with paving grade asphalt.
Roofing Grade Asphalt
Normally two coats of type R988 roofing asphalt is applied in two coats of 10mm. This gives a nominal thickness of 20mm. For extra security and protection an additional 10mm coat can be applied. This would bring the thickness to 30mm. This additional coat would be strongly recommended when the area will be inaccessible for roof inspection and repair work.
Roofing grade specifications are capable of withstanding pedestrian traffic for maintenance but will not be able to tolerate heavier demands. This includes stiletto heels, tables and chairs.
If the area is to be used for a terrace or a balcony an additional 10% - 15% grit would be required to make a more resistant surface. The way in which this will be done is with an initial 10mm coat of roofing asphalt which may contain extra grit. And then a second coat of 15mm grit reinforced roofing.
To endure heavy foot traffic, it is advisable to provide the asphalt roofing with suitable protection. There are two ways in which this can be done, the first is to lay suitable paving on top of the roofing asphalt. And the alternative is to apply paving asphalt on top of the roofing grade asphalt.
Both methods will give the balcony or terrace area the ability to withstand heavy foot traffic.
This coat is what will give the terrace or balcony the capability of withstanding heavier use.
*The first layer of roofing asphalt will be laid upon sheathing felt.
Sloping Surfaces on an Asphalt Roof
Sheathing felt can be used to provide separation on insulated and uninsulated roofs. If the roof is uninsulated separation can be provided up to a slope of 10 degrees. And if the roof is insulated, separation can be provided up to a slope of 5 degrees. If the slope is less than the angles mentioned previously, the roof can be treated as a normal flat roof.
However, if the angle is steeper laying asphalt upon the sheathing felt will cause problems such as slumping and creeping (this is where the as asphalt starts to slide down the slope due to the forces of gravity). If this is the case it is necessary to treat the asphalt work as if it were being applied to a vertical surface.
If the base is a concrete deck, a full bond to concrete is required. To achieve this the concrete should be lightly tamped or wood float finished.
If the base is a sloping timber deck. A firm attachment is achieved by applying the asphalt to expanded metal lathing. This metal lathing is fixed on top of sheathing felt and securely fixed to timber at 150mm centres.
The recommendation of a 5-degree slope for an insulated roof. And a 10-degree slope for an uninsulated roof are arbitrary numbers. In certain situations, a lesser or greater angle may be necessary. For example, a short slope in a shaded area may tolerate a greater slope whereas a long slope which is south facing will require a smaller slope.
Paving Grade Asphalt
As mentioned earlier paving grade asphalt can be added on top of two coats of roofing grade asphalt to provide an area with increase durability. The decision on whether to use a finishing coat of paving grade asphalt will be based upon the weight and type of traffic the asphalt will need to withstand.
In general, as the aggregate content of the asphalt increases, so does the ability of the asphalt to bear load. A natural consequence of an increase in aggregate requires an increase in asphalt to accommodate it. As a rule, for the percentage of aggregate added the amount of asphalt required should be that percentage in millimetres. So, for 30% aggregate, 30mm of asphalt will be required. This rule is not steadfast and is only a loose guide.
Paving Grade Asphalt for Podia and Public Access Decks
The absolute minimum thickness for paving asphalt is 20mm. This thickness of asphalt is suitable for podia and public access decks. When preparing asphalt for this type of application it will be laid on top of a 20mm of roofing grade asphalt. This would consist of two 10mm layers. The paving asphalt will be 25% aggregate content with an asphalt thickness of between 20-25mm. The aggregate will consist of grit which is 3mm in diameter.
Paving Grade Asphalt Roofing
In most situations. 30mm is the desired thickness of paving grade asphalt for roofs designed to accept light vehicle traffic and roof top car parking. The aggregate content in this instance will be 30%. If the specifier increases the thickness to 35mm, the aggregate content will go up to 35%.
The standard build-up for asphalt roofing to withstand light vehicle traffic and roof top car parking will be as follows:
1) A Glass Fibre Tissue Separating Layer
2) 20mm of roofing grade asphalt (2, 10mm layers of asphalt)
3) 30-35mm paving grade asphalt (with 30-35% aggregate content)
Paving Grade Asphalt for Service Decks
Service decks commonly found on the roof above retail space will require a 40mm coating of paving grade asphalt laid over two 10mm coats of roofing grade asphalt. This will give a combined total of 60mm in thickness. A total of 20mm in roofing grade asphalt and a total of 40mm in paving grade asphalt. The reason for this thickness being required is to endure the constant use of heavy vehicles such as fork lift trucks and lorries.
For 40mm thick paving grade asphalt the aggregate content will be 40%. However, in most cases there is no benefit of increasing the aggregate content beyond 40%.
The reason for this is paving asphalt is always likely to suffer some indentation and tyre marking under the wheels of parked vehicles. And the only way to prevent this would be to increase the aggregate content over 40%.
However, this increase in aggregate content creates other problems. Firstly, such a high content of aggregate will make the formation of bay joints extremely difficult. And secondly, this increase in aggregate content will significantly increase the risk of cracking.
Therefore, 40mm paving grade asphalt with 40% aggregate content is the best compromise for most service decks.
To reduce the risk of indentation pre-coated chipping can be scattered across the surface of the service deck then rolled in. The added benefit of this will be additional traction for the vehicles which operate on the service deck.
The other way in which traction and anti-skid properties can be added to the surface deck include the use of surface dressings which are epoxy resins combined with skid resistant aggregates such as fine grit.
The standard build-up on asphalt roofing to be used as a service deck, with the requirement of enduring heavy traffic:
1) A Glass Fibre Tissue Separating Layer
2) 20mm of roofing grade asphalt (2, 10mm layers)
3) 40mm paving grade asphalt (with 40% aggregate content)
4) Optional application of a surface dressing to add traction to surface.
Service Deck Vehicle Access Ramps
Service deck vehicle access ramps must endure extreme down slop forces due to heavy vehicle traction and braking as they descend from the roof. Due to these forces the mastic asphalt must be bound directly to the concrete surface of the ramp. The concrete on this ramp must have no joints and have tamp marks going across. The reason for this is to provide a key for the mastic asphalt to bind to.
Before work commences it is important to make sure the concrete is as dry as possible. Then prior to the first coat of mastic asphalt being applied to the concrete a limited amount of primer can be applied. It is important to note no sheathing felt is used on the vehicle access ramp of a service deck.
This first coat is roofing grade asphalt and will be to a thickness of 15mm. The next coat will be a 40mm coat of paving grade asphalt. The aggregate content of this paving grade asphalt will be 40%. The reason for the coat being 40mm thick is because of the heavy traffic the vehicle access ramp will endure as lorries travel up to the service deck.
The standard build-up for asphalt vehicle access ramps leading to roofs to be used as service decks:
1) Concrete ramp with tamp marks going across the slope
2) Limited high bond primer
3) 15mm of roofing grade mastic asphalt
4) 40mm of paving grade mastic asphalt with 40% aggregate content
Is an Asphalt Roof Good?
An asphalt roof is good for anyone who wants a seamless, carbon zero rated roofing system which has stood for test of time. Mastic asphalt roofing has proven to be the ‘King of Waterproofing’ over many decades.
How Many Years Does an Asphalt Roof Last?
An asphalt roof can last in excess of 50 years if it is maintained properly and installed by skilled craftsmen. Of course the lifetime of an asphalt roof will differ from roof to roof depending on the stress put upon it. You can see a video on our youtube channel inspecting some asphalt roofing 50 years later. To view this video click here.
Why is Mastic Asphalt Used on Flat Roofs?
Mastic asphalt is used on flat roofs as it has excellent waterproofing properties, is extremely durable and is environmentally friendly.
• We have our own mixer this means a flame free laying of the mastic asphalt roofing. Better consistency in the asphalt mixture meaning a more efficient installation process with a better overall finish.
• Vastly experienced 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 RJ Evans to provide a free no obligation quotation or any information related to asphalt roofing please contact us or call us now on 01277 375 511.
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