MASTIC ASPHALT INTRODUCTION FACT SHEET BY ROCK COMPLETE WATERPROOFING

Mastic asphalt is the ultimate protective material for a wide range of construction applications. Used for roofing, flooring, paving or tanking, mastic asphalt is capable of out-performing and outlasting all other comparable materials.

Rock Waterproofing’s mastic asphalt product range consists of either Flexiphalte Pommar polymer modified roofing grade mastic asphalt, Flexiphalte roofing grade mastic asphalt, or special high performance membrane materials overlaid with Flexiphalte modified paving grade mastic asphalt. All details can be obtained from the NBS J21 specification documents on Rock’s website.

INTENDED USE
Asphalting is one of the recognised specialist trades in the building industry and the type of asphalt primarily applied to buildings is known as mastic asphalt. Unlike the types of asphalt, mastic asphalt is laid without compaction, normally by means of a hand float. It is used to waterproof basements and roofs and for the lining of tank to contain water or weak industrial liquors. It is also extensively used to provide waterproof and hard wearing surfaces to balconies, roof top car parks and service decks and domestic and industrial floors. Mastic asphalt products are sold to the trade for these applications and it is assumed that customers will be familiar with normal trade practices concerning these applications. This would include knowledge of relevant Codes of Practice such as British Standard Code of Practice for Mastic Asphalt Roofing BS8218:1998 and the NBS J21 specification.

Specifically for roofing, a typical flat roof where mastic asphalt can be applied comprises of ceiling, structural supports, roof deck, waterproof covering and surface protection and incorporates insulation and drainage. It may support ancillary items such as engineering equipment, hand railing and lightning conductors.

Flexiphalte mastic asphalt from Rock Waterproofing delivers a level of protection that cannot be matched by any other type of roofing system or membrane, giving “lifetime” performance equal to the substrate upon which it is laid. Cover with ballast, paving slabs or both for a conventional inverted roof.

Mastic asphalt works, when completed, generally present low risks to building users. The risks which exist during construction can be effectively controlled when the works are undertaken by a specialist contractor like Rock Waterproofing in suitable conditions.

Mastic asphalt is not readily combustible, but the heat required to re-melt it can be a hazard. Properly handled, by fully trained operatives, these potential hazards are reduced to a perfectly acceptable low risk level.

MATERIALS
Major risks from materials used in mastic asphalt work and some appropriate control measures:

• Mastic asphalt is delivered to site either in solid block form or in a ‘Hot Charge’ tanker in molten form.
• Materials should be checked immediately they are received on site to ensure they comply with the specification and are correctly wrapped/labelled. Non-compliant materials should be labelled, recorded and removed from site.
• Mastic asphalt is not normally affected by ambient climate. Outside storage is acceptable. Pallets should never be stacked more than two high, on uneven ground or near other site hazards.
• Care should be taken when removing individual blocks from the stack. Safety footwear and gloves should be worn. If stacked at roof level, the bearing capacity of the roof or scaffolding must be checked to ensure no overloading takes place.

REMELTING
For remelting, the blocks should be broken into suitable sizes by use of a club hammer or mallet. Goggles should be worn for protection against splinter chips. Care should be taken to ensure that smaller broken pieces do not fall onto other people.

Blocks should be remelted to the correct laying temperature of 200°C to 230°C. Strict temperature control should be maintained throughout the remelting process. Generally, temperatures should not exceed 230°C.

When adding smaller pieces to molten material in the cauldron or mixer, great care should be taken in order to avoid “splashing”. Gloves should be worn at all times.

The heat to remelt is normally supplied by propane gas or diesel fuel oil, and this should be started in the correct manner as laid down by the LPG safe storage and handling regulations.

Regular temperature checks should be made and recorded by the mixerman/potman to ensure no overheating. Thermometers must be re-calibrated at least every six months and records kept.

Fires must be extinguished at least one hour before the mixerman/potman leaves the pot or mixer to ensure no smouldering can occur leading to later conflagration. When a hot work permits system has been agreed, permits should be filed in and recorded with the site manager.

TRANSPORTATION
Molten mastic asphalt should be transferred into purpose-made sturdy buckets by means of ‘dipping’ into a cauldron, or by the banjo on a mixer. Care should be taken to avoid burns or spillage.

Buckets should be carefully cleaned and stored in order to maintain them in good working order. Damaged buckets should be discarded.

Gloves and boots should always be worn when carrying and/or tipping out buckets of hot mastic asphalt.

Suitable safety tools should be used when buckets are to be hoisted. When wheeled, proper bucket trolleys should be utilised. Buckets should not be wedged into wheelbarrows.

EQUIPMENT
Mixers should be in a good condition, regularly serviced and maintained and with well-fitting lids.

Cauldrons, with appropriate properly fitting lids, should be stood in a correct sized tray on suitably fl at hard standing, filled with dry sand to contain the heat. Old, badly worn or damaged cauldrons should not be used.

FIRE EXTINGUISHERS
At least two dry powder fire extinguishers should be located adjacent to the remelting equipment at all times which should be regularly checked and replaced after use. They should be rechecked and dated at least every six months by a competent extinguisher agent.

Operators should be trained and certificated in the use of these fire extinguishers.

PROTECTIVE CLOTHING
Hot mastic asphalt and gas burners can cause severe burns. Operatives should be instructed in their correct use and protective clothing, including gloves and footwear should be worn. First aid equipment should be available.

COMPOSITION
The materials used in manufacturing mastic asphalt include:

1. Asphaltic cement which consists of bitumen, lake asphalt, asphaltite or blends of these with one another or with flux oils
2. Fine aggregate. This will be a naturally occurring consolidated stratified calcareous rock
3. The coarse aggregate consists of clean igneous or calcareous rock or siliceous material obtained from natural deposits either directly or by screening, crushing or other mechanical process
4. Certain grades of mastic asphalt are polymer modified and some may include colouring pigments. Proprietary products are used for these purposes.

The bitumen essentially contains hydrocarbons and their derivatives and is soluble in carbon disulphide. It is substantially non-volatile and softens when heated. It is brown/black in colour and, apart from the Trinidad Lake Asphalt, it is obtained from a refinery process from petroleum. The composition is best described by separation into broad chemical components as follows:

1. Asphaltenes - brown/black amorphous solids containing mainly carbon and hydrogen and also nitrogen, sulphur and oxygen. They are aromatic materials of high molecular weight, typically 2,000 to 5,000
2. Resins - adhesive, solid or semi-solid, dark brown in colour and very polar in nature, containing mainly carbon and hydrogen and small amounts of nitrogen, sulphur and oxygen. Molecular weight typically 900 - 1,300
3. Cyclics - viscous liquids comprising largely carbon and hydrogen, but also some sulphur, nitrogen and oxygen. Their molecular weights are typically 550 – 850.

For more information on flat roof waterproofing including mastic asphalt contact Rock Complete Waterproofing.   www.wearerock.co.uk

Full NBS J21 specifications and BBA certificates for roofs and car parks are also available on our website.