Rooftop waterproofing can be achieved with various sealants. Bituminous sheets (bituminous membranes) are considered to be the most suitable, because they have excellent adhesion to all building materials without exception and offer long-term waterproofing.
Bituminous sheet are manufactured in different qualities so that they can be afforded by everyone and the whole range of waterproofing applications in a building. Bituminous sheets are manufactured for masonry and basements, roof gardens, to be used as vapour barriers, as the first layer in multi-layered waterproofing system, etc.
The bituminous sheets that will be used to waterproof rooftops or a rooftop building, should have the following specifications:
- They should have high density per square metre.
Bituminous sheets are manufactured in different densities: 3 Kg, 4 Kg, 4.5 Kg, 5 Kg, 6 Kg. The heavier the bituminous sheet, the thicker the waterproofing layer and the better protection over time.
- It should be elastomeric with great flexibility in the cold.
When the bituminous mixture of the bituminous sheet is elastomeric, it is able to absorb the contractions and expansions of the underlay. Bituminous sheet that are highly flexible in negative temperatures e.g., -20 oC, are not affected and do not crack in intense temperature fluctuations and frost.
Bituminous sheets are manufacture for 0 oC, -5 oC, -10 oC, -15 oC , -20 oC.
- They should have strong polysteric reinforcement
The reinforcement is what gives the corresponding mechanical strengths to the bituminous sheets, i.e., how much they can be elongated before breaking (elongation at break), the extent of the forces that must be exerted to break (tensile strength), how easily they will pierce (resistance to perforation) etc.
The best reinforcement is considered to be the spundbond (180 gr / m2) with longitudinal glass fibres.
- It should have suitable coating
When the bituminous sheets remain exposed to solar radiation, they should coated with a white tile for better protection.
When the bituminous sheet is placed under cement mortar or concrete, it should be coated with polyurethane.
Successful waterproofing does not only depend on the quality of the bituminous sheet that will be used, but also by the professional training and the construction experience of the insulation work crew carrying out the project.
It has been observed that the economic crisis brought an influx of people from similar or unrelated professions without the necessary knowledge or who know of a one-size-fits-all insulation method, without being able to perceive the causes of the problem and the different factors that prevail from project to project.
The lack of experience and knowledge of technical specifications lead to tragic errors and oversights at the cost of the insulation's longevity.
Some poor application examples include:
- When the bituminous sheets are not adhered correctly.
- When the bituminous sheets are adhered on the wrong side.
- When the overlapping of the bituminous sheets runs contrary to the water flow thus preventing its flow to the down spouts.
- When a cross is formed at the overlapping.
The sheets must be placed in such a way that the overlap of their width is perpendicular to the middle of their adjacent bituminous sheets (like with bricklaying).
- When special pieces are not places in areas where insulation is interrupted, such as: Pipe sleeves, pipes that penetrate the concrete, railings, bases from solar panels and tanks, downspouts, etc.
- When waterproofing stops low down on the parapet.