Waterproofing Elevator Shafts

Structural waterproofing for lift pits is a requirement. The design details must take into account that the pit and shaft are intrinsic to housing the elevator. As generally speaking, a lift shaft extends at least 1.5 meters below the lowest level floor slab, and sometimes as much as 2.5 meters or more if travel time is more than 30 meters, to provide the necessary space for equipment and machinery, this means that the lift pit will need to reach beyond the sub-slab capillary break and water collection system. Therefore, beyond specifying the right concrete waterproofing product for a lift pit, it’s important to think about the complete concrete waterproofing system.

Construction joints and other details must be carefully studied to avoid problems arising in the future. Defects and cracks in the structure due to structural movement or general deterioration of the construction components such as the concrete or water bar will allow water to pass into the pit. As a matter of fact, the water table, which is the section of ground where the soil is permanently saturated with water, will impact any structure below ground. A space at or below the lift pit essentially creates a ‘floating box.’ ‘Perched water’, which sits on an impermeable or low-permeability soil layer above the water table, will travel laterally on these layers. Heavy rainfall may cause the water table to rise as rainwater permeates down to reach the water table. As it travels, it may reach a wall below ground and leak through cracks in the wall. Water ingress may become more likely as the water table level is modified by construction structures being erected around a building.

The concrete must be watertight. It must be well compacted and designed with low water-cement ratios. Substandard concrete will allow water to penetrate, causing steel reinforcements to corrode and thus weakening strength requiring eventually costly structural repair works. It is essential that works be carried out by experienced subcontractors, as very often space is restricted and work conducted in difficult conditions.

Holderchem offers for this type of application Batimix and Vandex products These include crystalline waterproofing products, which become an integral part of the concrete through a crystallization process. They are applied to either the positive or negative side of the substrate. Crystal growth occurs, blocking the capillaries and minor shrinkage cracks within the concrete to prevent any further water ingress. It also supplies versatile waterproofing and repair mortars for concrete and masonry (tested in accordance with BS EN 1504-3), which may be applied to horizontal and vertical surfaces using a trowel or by spraying.

Good housekeeping practices to avoid internal water sources leaking are also recommended.