A waterproofing membrane is a thin layer of water-tight material that is laid over a surface. This layer is continuous and does not allow water to pass through it. For example, on a flat terrace, a waterproofing membrane could be laid above the structural slab and below the finish tiles. This will ensure that water does not seep into the structural slab. The tiles and membrane must be laid over a filler material that is sloped to ensure that water flows into sumps and drains. Any water that remains as puddles over the tiles is likely to seep into the slab over time, so puddles are to be avoided at all costs.
waterproof membranes are composed of thin layers of waterproof material. Most are about 2 to 4mm thick. There are essentially 2 types of membranes, sheet based membranes and liquid applied membranes.
Ideally, a waterproofing membrane should be strong, flexible, tear-resistant and elastic so that it can stretch to cover cracks and also move with the building. If the membrane is to be exposed to the sun, then it should be UV stable. waterproof membrane should be flexible enough to take any shape it is laid over, and be capable of turning up and over walls and other construction features.
SHEET BASED WATERPROOFING MEMBRANES
These are Sheet based waterproofing membranes which arrive at the site in the form of rolls. These are then unfurled and laid on a firm surface. The most common type of sheet based membrane is a bituminous waterproofing membrane. This type of membrane is stuck to the substrate with a hot tar based adhesive using blowtorches.
Joints between adjacent membranes are also made with the same hot adhesive. The sheets are overlapped by about 100mm (4") to form a waterproof joint. Some membranes are even joined by melting them with a hot air gun and then overlapping them on the previously laid sheet.
With this type of membrane, joints between sheets are critical, and must be done perfectly to avoid leakage.
Other types of sheet based membranes are PVC membranes and composite membranes. The latter have a fabric base that provides strength and tear resistance, and a chemical that coats the fabric to provide resistance.
Since these membranes are factory-produced excepting the joints, they are consistent in quality.
LIQUID APPLIED WATERPROOFING MEMBRANES
Liquid applied Waterproof membranes come to the site in liquid form, which are then either sprayed or brush-applied on the surface. The liquid cures in the air to form a seamless, joint-free membrane. The thickness can be controlled by applying more of the liquid chemical per unit area.
Since the application procedure is very quick, a contractor will try and finish the entire area to be waterproofed in a single day to avoid cold joints. However, if a very large area is to be done on successive days, cold joints can easily be done by overlapping the new membrane over the old - the chemical will stick to itself readily.
These are generally considered to be superior to sheet based membranes as they are joint-free. However care must be taken in application to provide just the right thickness. The membrane can tear or break if it is too thin.