Waterproofing a roof is the process of making a roof structure water resistant so that it remains unaffected by rainwater with no stagnation or water leakage inside a building.
Most roofs in Mauritius are made of concrete which deteriorates over time due to corrosion of the embedded steel bars resulting in cracking and becomes less water resistant.
A roof can be waterproofed using an efficient drainage system or using waterproof membranes or coatings/liquids to repel the water.
1. Good roof drainage
Poorly designed drainage systems tend to get blocked easily and therefore does not efficiently drain water away causing accumulation of water which facilitate corrosion and leakage through the concrete roof.
Flat roof can be given a very low slope using a new cement layers to drain rainwater away and scupper drains can be constructed along roof sides where water accumulation is prone as shown in figure 1 below.
It is a preventive measure to increase concrete roof durability in terms of water resistance but could be costly.
2. Bituminous (hot melt oxidised bitumen) / Liquid Bitumen waterproofing
It is the most used type of waterproofing which consists of applying bituminous membranes made of: -
- Bitumen acts as waterproofing agent
- Mineral granules to protect against UV radiation
- Polymers to give elasticity
- Filler to give rigidity
- Plastic layer to avoid stickiness
It is normally applied by rolling and adhering the membrane on the roof surface using torching or hot air welding or sometimes with solvent-based adhesives methods. Sometimes solvent based bitumen primer (liquid) is applied on complex roof where membranes cannot be laid or even flat surfaces.
Newer self-adhesive aluminium foil bitumen waterproofing membrane is also common nowadays by just peeling and sticking the membrane to the roof for ease of application. It also acts a thermal insulation to reduce heat gain in a building.
SBS bitumen (asphalt) shingles are also available for incline shingle roofs with self adhesive points for bonding, easy installation and large range of colours.
It is low-cost, flexible, durable and could be easily applied to flat surface. It cannot be torn off easily compared to rubber membranes. It exhibits “solid” characteristics at ambient temperatures and provide superior adhesion.
Benefits: - It is extremely water resistant and also fire resistant compared to bituminous membranes.
4. Acrylic elastomeric coating or Polyurethane waterproofing
Polyurea is a type of elastomeric coating that is poured onto a roof and is spread with a roller over the surface to make it waterproof.
It is strong, chemical resistant and flexible enough for the membrane to contract and expand with the roof substrate. It is a fast application, permanent and will not degrade under harsh UV rays or winds.