Asphalt is a great material to use to waterproof any flat roof. Mastic asphalt has a proven track record as a capable waterproofer. This has led to this phenomenal flat roofing material earning the name 'The King of Waterproofing' (this makes it the go to system for many specifiers above newer systems such as EPDM rubber roofing). Below we will look at the stages of installing an asphalt flat roof.
Asphalt is a tough, hardwearing and versatile material, which can be used on top of a variety of surfaces such as concrete, metal and timber - making it a popular choice for flat roofs. Further to this, it has the desirable carbon rating of zero and is one of the strongest waterproof materials around. For years, mastic asphalt has been a popular choice for not just flat roofs but also car parks, flooring and pathways. This blog will explore how an asphalt flat roof is laid: looking in detail at the preparation process, how asphalt roofing is treated and how its life can be extended.
Preparation is a key part of the asphalt roofing installation process. It is vital that you take these steps to ensure the best possible flat roof is achieved:
• Firstly, carefully sweep any debris or fragments away from the area that is about to be roofed.
• Then, make sure your metal buckets have been dusted with cement and placed near the asphalt mixer.
• Next, prime the roofs skirting.
• Finally, set out the sheathing felt and battens ready for the asphalt to be poured and spread.
Asphalt is packaged in blocks and following the delivery of the asphalt, the operatives will unload these blocks and positioning them as close the mixer as they can. Then, they work by hand to break up the mastic asphalt blocks into quarters using their sledgehammers. Their aim is to make the blocks small enough that they can be put into the mixer ready for heating.
In order to comply with health and safety procedures the foreman will ensure that the gas powering the asphalt mixer is a safe distance from the burners, this distance is set to at least 3 meters. In the unlikely event of the gas catching fire, at least 2 fire extinguishers1 are kept close to the burners to be used to contain the fire spreading.
The heating process:
Workmen place the broken-up mastic asphalt pieces into the mixer and apply the gas to heat the mixer. As the mixer begins to heat the blocks begin to form into one large mallable mass. The workers now have to agitate this mass to ensure it is able to reach the right texture that allows it to flow and be poured on to the roofing area.
Roofers carefully watch the mastic asphalt at this point in the process and monitor its temperature. The desired temperature needed to lay the asphalt is 220 degrees. It is essential workers then keep the mixture at this temperature consistently, in order to achieve the perfect roof; if it is allowed to get any higher it may burn and effect the consistency of the asphalt, which will make it harder to manipulate and lay over the desired area.
Transporting the mastic asphalt:
Before workers begin to transport the hot, mailable asphalt they dust their metal buckets with cement to form a protectant seal which allows the melted asphalt to flow out of the bucket freely and steadily. Dusting the melt buckets also prevents any mastic from sticking to side of the bucket, thus reducing the level of waste.
The process of laying the mastic asphalt roof:
The desired area for the asphalt flat roof will have been prepared by workmen with wooden battens and sheathing felt2. Once the asphalt reaches them they will pour it onto this area in two-meter-wide lap. As soon as one workman begins to pour the mastic asphalt another will use their handmade float to spread the hot mastic across the roofing area.
Roofers will have their own handmade floats that they use to not only spread the mastic asphalt, but also to regulate the consistency and thickness of the asphalt as its laid; they will be aiming for a 10mm height across their roofed area as well as ensuring that there is a smooth, polished look.
Whilst the workers on the roofer are pouring and spreading the melted asphalt onto the flat roof area back on the ground there will be another team working to produce the next batch of mailable asphalt ready for the roofers.
When it is time for the roofers to lay the next section of the asphalt flat roof they place the new batten 100 mm inside of the previous coat to ensure there are no gaps and it is all bonded together. They then repeat the same process as before, with one team pouring the melted asphalt out of their metal bucket, whilst the other uses their float to spread it consistently across the surface. It is essential that each new batch of malleable mastic asphalt is ready to lay immediately that the roofers finish with the previous roofing section, as this will prevent any contamination between the sections and any water getting under the surface.
The use of coarse rubbing sand
Once the hot asphalt has been laid workers will spread coarse rubbing sand3 across the asphalt roof with a laying float. The sand acts as a barrier that prevents any of the bitumen inside the asphalt from surfacing, as if this were to happen the reaction would spoil the flat roofs smooth finish. This includes crazing and premature fading of colour.
Lots of people choose to complete their asphalt roofs by adding a final layer of UV solar protective paint. This paint reflects the unwanted side effects of the sun’s heat such as the sun’s warmth heating the roof and drawing the bitumen to the surface. Further to this, the repeated heat exposure of the sun (solar radiation) can cause the asphalt flat roofing to suffer from slumping. It is recommended that you add a layer of UV solar protective paint to your asphalt roof every 3 to 5 years to give your roof the best length of life possible.
If you would like a quotation or any information regarding the repair, maintenance or installation of an asphalt flat roof please get in touch with us via our contact page or call us now on 0207 781 8150. One of our friendly team will be happy to assist you.