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Asphalt Surface Protection

When laying mastic asphalt it is extremely important to ensure sufficient asphalt surface protection to maximise the longevity of your roof.

On horizontal asphalt work a sand rubbed finish will finish the application. If there is no insulation any extra treatment is not needed to sufficiently protect the asphalt. However, in most cases we recommend finishing all asphalt with solar reflective paint.

If asphalt is used for a warm roof with an efficient insulating layer beneath it will have to endure more extreme temperatures. During the warmer summer months, it will endure higher temperatures due to the low heat loss from the underside. And in the colder winter months it will be colder because of the absence of a stabilising thermal mass beneath.

Asphalt Surface Protection in High Temperatures

A solar reflective paint coating is imperative on warm roofs and recommended on all asphalt roofs. This is because during the first few years of service asphalt is not fully hardened. And these extreme changes in temperature will cause the asphalt to endure a lot of movement.

If this solar reflective coasting is not required the asphalt can feel extremely spongy underfoot on hot days. The problem with this kind of movement is the asphalt can suffer from slumping, or even cracks due to drastic changes in temperature overnight.

An extremely important detail with solar reflective paint is around any lead flashing. The lead flashing should be covered in the coating as well as the asphalt which it covers. If this is not done the lead which conducts heat will increase in temperature which will then in turn heat the asphalt and lead to an extremely high probability of slumping. This obvious develops the potential for water ingress

Another problem with exposure to the sun is the drawing out of the bitumen which can lead to the roof having a worn grey look making it look many years older than it is.

Asphalt Surface Protection in Low Temperatures

Solar reflective paint also serves to protect asphalt roofing in low temperatures. The way in which it does this is to minimise the maximum temperature of the roof. Therefore, minimising the amount the roof drops when it goes towards its minimum temperature. An example of this would be going from a high temperature during the midday sun in winter to minus temperatures overnight.

How Often Should Solar Reflective Paint Be Re-Applied?

To maximise the longevity of your roof is it recommended to re-apply solar reflective paint to the surface of an asphalt roof every 3-5 years. If your asphalt roof requires a re-coating of solar reflective paint please call us on 01277 375 511 or email us and we will be happy to assist you.

Surface Protection with Stone Chippings

With an asphalt warm roof, stone chippings are an alternative to solar reflective paint. New light coloured chippings can perform almost as good as white solar reflective paint. These chippings will darken over time but will remain effective for the life span of the mastic asphalt roof.

The drawback of stone chippings is when they are deeply bonded to the asphalt surface. This causes difficulties when carrying out repair work.

Asphalt Surfacing for Promenades

In conditions where a constant flow of traffic is expected asphalt surfacing can be finished with concrete tiles or paving. The smooth asphalt surface provides a good base for concrete tiles bedded in bitumen. The tiles should be laid with a gap of a few millimetres at each joint. For paving tiles bedding is normally done in sand and cement. Here it is necessary to use a layer of building paper to legislate for the movement between the paving and asphalt.

Both concrete tiles and paving should allow for expansion. The way in which this is done is by setting them 25mm back from the perimeter of the roof and any detailing. There should also be expansion joints at 3metre centres.

Alternatively, paving can be supported with polyester felt. This is better than using plastic or rubber corner supports as they can become indented into the asphalt. Another advantage of shims of polyester felt is it isolates the paving from the asphalt and provides drainage.

All tiles and paved roofs should have a minimum fall of 1:80 to provide adequate drainage. If the paving or tiles are bedded in bitumen 1:40 is the maximum fall advised. The reason for this is to prevent any slippage in high temperatures.

Asphalt Surfacing for Terraces and Roof Gardens

For the waterproofing of roof gardens and terraces 3 coats of mastic asphalt is the most suitable specification. The reason for this is because locating and repairing leaks will be both difficult and expensive.

Before a roof terrace or garden is constructed the whole surface must be waterproofed with mastic asphalt. This work must take place in favourable conditions. Once the asphalt waterproofing is finished the membrane must be tested for water tightness. Only when the surface is passed as watertight can the construction of the roof garden or terrace begin.

It is a good idea to make all aspects of the roof garden or terrace construction to be removable in sections. The reason for this is to minimise the disruption and expense of any leaks which develop in the future.

Asphalt Surfacing of Inverted Roofs

Asphalt is a great material for inverted roofs. The insulation above the asphalt helps produce a stable temperature for the asphalt. This protects the asphalt from the problems it can suffer due to fluctuations in temperatures.

With an asphalt inverted roof the insulation must be completely resistant to deterioration in the continuous wet conditions it will face. And in most cases, it will need protection from UV radiation1. A 50mm coat of gravel or 50mm thick paving will provide suitable UV protection. Paving should have thick polyester felt pads in the corners where it meets the insulation. The use of either gravel of paving will also provide the insulation with protection against strong winds.

The material most commonly used for insulation on inverted roofs is extruded polystyrene2. This is because the material has extremely good moisture resistance with a relatively small loss of thermal insulation from the small amount of moisture absorption that occurs.

The insulation on inverted roof should not be bonded directly to the asphalt. There should be a separation fleece3 in between them. The reason for this is to prevent any joint movement putting stress on the asphalt and risking the asphalt waterproofing being compromised.

The joints in the insulation will gradually fill with silt as rainwater percolates through the roofing system. It is not practical to prevent silt forming in voids in joints or under the insulation. However, if gravel is placed above the insulation, it is important to control the gravel travelling to the underside of the insulation.

The way to do this is with a filter layer being added under the gravel to restrict the amount of gravel which travels down towards the insulation.

With an inverted roof, it is not advisable to finish the roof with an open edge. They should be finished against skirtings or edge curbs.

An inverted roof should be drained at two levels. Once at the top surface of the insulation and then at waterproofing level. The waterproofing level of an inverted roof should always be laid to falls.

Need Any Advice on Asphalt Surfacing

If you require any more information about asphalt surface protection or require a quotation on an upcoming asphalt roof please get in touch with our specialist asphalt team by calling 01277 375 511 or emailing us directly .

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