Delta: Lift Pit Waterproofing – Type A solutions

Delta Membranes has recently worked on a project whereby the scope was to provide a waterproofing solution to a newly constructed lift pit for a four-storey residential block.

Elevators in buildings carry thousands of people yearly, ensuring safe transport to their floors. These elevator cabs operate efficiently to keep the whole system running smoothly. The elevator pit (lift pit) is a crucial part of the lift that ensures safety in case of an accident and makes it easier for the technicians to inspect, repair, and maintain its various parts. A lift pit is a small space at the bottom of a elevator shaft that supports the lift car and its mechanical systems, similar to a basement.

The lift pit, constructed from waterproof reinforced concrete (‘RC’) a Type B, waterproofing protection, extended 1.2 metres below ground level with a 1.4m x 1.4m footprint. Due to the nature of lift pit construction, seepage can occur at the wall-floor junction due to high adjacent ground levels. 

Factors

Designing an effective waterproofing system requires the addressing of several factors, including the building’s final use, the British Standard waterproofing grade, structural considerations, and building warranty provider requirements.

Waterproofing is crucial for any structure below ground, fully or partially, to protect and preserve its integrity.

The BS 8102:2022 ‘Protection of Below Ground Structures Against Water Ingress’ is the code of practice for structural waterproofing, offering essential recommendations and guidance.  

Delta Registered Installers, AJ Waterproofing Services, were appointed to join the design team as Waterproofing Design Specialists, ensuring a reliable and watertight solution for this project.

Waterproofing Design Specialists assess the application of waterproofing protection methods. A combination of waterproofing solutions may be suggested. 

When combining systems, The Waterproofing Design Specialist ensures the systems specified have different performance characteristics to reduce failure risks from common causes. Assessing the compatibility of protection types to minimise risks and avoid remedial measures.

Methodology

Following preliminary site inspections, this project required a specialist system to provide an efficient, compliant and future proof approach. Discussions were held on waterproofing solutions available, methodology for works and cost.   

Lift pits are particularly vulnerable to water ingress as they sit at the lowest part of a building. Additionally, lift shafts are subject to vibrations from elevator movement, which can affect both the structure and waterproofing solution over time. To mitigate this, materials with flexibility and load-bearing capacity were prioritised.  

Construction joints and penetrations within a Type B construction require special consideration as they are considered the weak areas. They are usually detailed as part of the overall design using hydrophilic strips, water stops or injectable hoses.

Exposed steel reinforcement steels can be protected from corrosion, fire, and other damage using a variety of methods. 

NB 1 Grey

Working closely with Delta’s Technical Team, AJ Waterproofing Services specified Koster NB 1 Grey as a primary waterproofing layer. Koster NB 1 is a BBA Approved mineral coated waterproofing slurry with crystallising and capillary-plugging agents. It’s ideal for waterproofing against ground moisture, non-pressurised, and pressurised water (sealing against pressurised water (> 13 bar). NB 1 Grey is characterised by its excellent resistance to pressure and abrasion as well as chemical and sulphate resistance.  

Systematically prepared

Before applying Koster NB 1, all substrates were systematically prepared. Concrete surfaces were bush hammered for a rough texture, with surfaces were washed clean, and an application of Koster Polysil TG 500. New concrete may contain free lime, or uncombined calcium oxide. This can cause the concrete to expand, leading to durability problems and future maintenance costs. Applying an ‘anti-lime’ coating to new concrete, especially in basements or where underpinning is used, prevent free lime from leaching.

A 45-degree fillet of Koster Repair Mortar Plus was applied at the wall-floor junction to seal the vulnerable area and protect exposed reinforcement.

Once the Koster NB 1 had cured, two coats (layers) of Koster NB 1 Elastic Grey were applied. This flexible slurry filled any hairline cracks and accommodated micro-movements caused by lift vibrations, preventing future damage.

Koster Products Used

– Polysil TG 500
– Repair Mortar Plus
– NB1 Grey
– NB1 Elastic Grey 

Case Study Results 

The waterproofing installation was completed efficiently in three days, facilitated by the straightforward application process. The project remained on budget, meeting both cost expectations and technical requirements.

Delta Membrane Systems,
Delta House,
Merlin Way,
North Weald,
Epping,
Essex,
CM16 6HR
United Kingdom

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