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London Asphalt offer a complete asphalt flat roof installation service. No matter how big or small your flat roof is our professional team will be happy to help you. With a wealth of experience and insurance backed guarantees you can be sure any work carried out on your flat roof will be to a high standard, completed as agreed and problem free for years to come.
Asphalt roofs are durable, hard-wearing and possess a track record which has stood the test of time. It can be used on a range of surfaces including timber, metal and concrete. Below we will look at how flat roofs in mastic asphalt are laid. Mastic asphalt is a popular choice to use for a flat roof because it's excellent waterproofing properties and having a carbon rating of zero1. Due to its versatility, mastic asphalt is a roofing material suitable for waterproofing a flat roof in a number of different scenarios, including service decks, car parks, and all manner of domestic and commercial roofs.
In order to achieve the best possible results, it is essential for the roof area to firstly be cleaned:
• Any debris or rubble needs to be swept away from the flat roofs substrate.
• The skirting needs to be primed.
• The sheathing felt and battens need to be set out in the correct places ready for the asphalt to be poured and spread.
When the delivery of the mastic asphalt reaches the site where the asphalt flat roofs going to be laid, the asphalt specialists will unload the blocks by hand and place it close to the asphalt mixer.
Now it is time for the roofing team to break up the mastic asphalt blocks by hand using a sledgehammer or a club. The workers will typically aim to turn the mastic asphalt blocks into four smaller pieces that can then be put into the mixer.
The first thing that needs to be done is for the gas powering the mixer to be set at least three meters from the gas cannisters to comply with health and safety regulations. Further to this, two fire extinguishers need to be kept close to the gas ready to be used if needed.
Now the broken-up mastic asphalt can be put into the asphalt mixer ready for heating. The lit mixer will then begin to warm up and melt the mastic asphalt blocks2 and make them form into one large mass. This mass will then need to be agitated so that it is able to flow and be poured on to the roof area.
Roofers have to be careful to watch the temperature so that the asphalt does not burn. Once the mastic asphalt is fully agitated and ready to be laid (this will occur at the point where the temperature of the asphalt is 220 degrees). The temperature of the mastic asphalt needs to be monitored so that it remains a constant heat. This will ensure the mastic asphalt's consistency remains the same so that it can be laid smoothly.
Metal buckets are required to transport the asphalt to the roof and the asphalt spreader's first job is to dust their metal buckets with cement. The cement will help ensure the melted asphalt is able to flow out of the bucket freely and does not stick to the side of the buckets.
Once the asphalt reaches the roof one of the spreaders will pour the mastic asphalt in a two-meter-wide lap in area which is to be waterproofed. This area would have been marked out by wooden battens and sheathing felt will have been laid down ready for the mastic asphalt to be applied (the purpose of the sheathing felt is to allow movement between the asphalt surface and the substrate).
As soon as the asphalt is poured, the spreader will begin to use his float to spread the mastic asphalt. The floats are used to regulate the thickness of the asphalt as it is being applied. The specialist will ensure the asphalt flat roof's first coat will be to a thickeness of 10mm across the marked-out area.
As this process is ongoing, the operative operating the asphalt mixer is breaking up the next lot of asphalt blocks with his sledgehammer. Turning them into quarters that he can then use to refill the mixer ready for the top coat of mastic asphalt. He will follow the same meticulous approach of carefully monitoring the mixture to ensure the correct temperature is achieved to make a consistent mixture that is free flowing.
Meanwhile the roofers will be placing a new batten which is a 100mm inside of the first coat. Once this is in place they repeat the earlier procedure of one worker pouring the hot asphalt from the metal buckets and the asphalt expert using his float to spread it and achieve the correct thickness. It is always best for the second layer to be done straight away to avoid any contamination or water getting between the surfaces.
The penultimate stage is to spread coarse rubbing sand across the asphalt roof using a float. This stage is necessary to avoid any of the asphalt’s bitumen from surfacing. The reason workers have to avoid bitumen surfacing is because of how it reacts to moisture. If sand has not been rubbed following the first rainfall bitumen will be pulled to the surface by the puddles and moisture left by the rain. The reaction to the rain water and the bitumen surfacing cause the asphalt to become a paler grey colour and causes crazing (crazing makes the asphalt look as though it has continuous cracking.) Crazing is an issue which is not unique to asphalt flat roofs, it can occur on any mastic asphalt application such as flooring, balconies and walkways.
Finally, it is always best to finish asphalt flat roofs by adding a final coat to your roof of UV solar protective paint. This layer of paint is a great way to reduce any of the unwanted effects the suns heat can cause.
But what are the negative side effects of the sun?
Over time, the sun can create issues for any asphalt roof. The warmth of the sun on surfaces of the flat roofs will heat the mastic asphalt. Over time this exposure causes the bitumen in the asphalt to be drawn to the surface. As mentioned previously when the bitumen is pulled to the surface various issues can arise, the roof’s finish becomes greyish and crazing can appear.
In addition to this the sun’s exposure to the flat roof can cause the asphalt to slump. When the sun then begins to set and the temperature drops this sudden change can cause the roof to begin to develop cracks as the asphalt contracts from its previously expanded state.
It is always good to re-coat any asphalt flat roof with a layer of UV solar protective3 paint every 3 to 5 years. This will help your flat roofing give the best lifespan possible.
If you require any further information or advice about mastic asphalt roofing, whether it’s the installation of a new asphalt flat roof or repair work to any existing flat roof please do not hesitate to get in touch. You can contact the team at London Asphalt by clicking here or calling us on 07739207726. One of our friendly team of asphalt experts will be happy to help you.