Asphalting Techniques

Here we look at various asphalting techniques. Asphalting is the most difficult of the roofing trade. This craft has a fine tradition and takes years to master. An asphalter must go through a long apprenticeship and years of training to be considered skilled at their trade. This is one of the main benefits of having a project waterproofed with mastic asphalt. The project is being carried out by highly skilled operatives.

Unfortunately, in the roofing industry this is not always the case, for example some liquid systems only require a two-day course to gain a qualification. Of course, the gulf in quality of work and the longevity of the any roof installed by operatives with such different backgrounds is clear to see.

The Preparation of Mastic Asphalt

Asphalt blocks are taken to the site where the waterproofing is to take place. Depending on the size of the job mechanically agitated mixers or cauldrons will be used to melt these blocks. On smaller jobs a cauldron may be used but on bigger jobs it will nearly always be a mechanically agitated mixer.

Before being added to the mixer or cauldron the asphalt blocks are broken up into smaller pieces. This is normally done with a club. Once in the mixer the asphalt will be heated until it is molten. The asphalt is normally ready at a temperature of approximately 230 degrees Celsius. For detail and vertical work this temperature will be lower to prevent the asphalt running excessively upon application.

As the molten asphalt is drawn from the mixer or cauldron more blocks are added. The asphalt which has been drawn is transported to the area which is to be waterproofed. The transportation method is either wheelbarrow or bucket (this will depend on the location of the waterproofing and the amount of access). The inside of the either the bucket of wheelbarrow will be dusted with limestone powder.

The reason for this is to make it easier for the asphalt to be removed. Without this limestone powder, there would be more adhesion between the asphalt and the surface of the bucket or wheelbarrow.

Order of Work

Most of the time with asphalt roofing, horizontal work is carried out before detail and vertical work. However, in some situations such as early mornings in low temperatures the asphalt may be too cool to lay mastic asphalt horizontally. If this is the case vertical or detail work may be carried out first. This is entirely down to the judgement of the asphalter leading the job. With insulated mixers, this is rarely a problem as they can be left charged with hot asphalt at the end of the day and maintain the asphalt’s temperature overnight.

With mastic asphalt steps the side stringers and risers will be coated with roofing grade asphalt before horizontal work is carried out on the treads. You can learn more about this process by clicking the following link: Asphalt Steps.