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Sheet waterproofing membrane: As the name implies, these are waterproofing membrane membranes that arrive at the site in the form of rolls. These are then unfurled and laid in an area. The most common type of sheet based membrane is a bituminous waterproofing membrane. This type of waterproofing membrane is stuck to the substrate with its molten part of bituminous using blowtorches.
Joints between adjacent membranes are also made with the same molten bituminous. The sheets are overlapped by about 100mm (4″) to form a waterproof joint.
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 membrane: Liquid applied 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.
The membrane can tear or break if it is too thin. The adhesion of the membrane to concrete must be good.
If a concrete screed (layer) is to be applied over a waterproofing membrane, the membrane is made rough by sand broadcasting. This is throwing a thin layer of sand by hand over the wet membrane (before it has set fully) so that the sand sticks to the membrane and provides a rough surface the concrete can adhere to