Lift pits (also known as lift wells) nearly always extend below floor level, so the same techniques as basement construction should be employed for their construction – including waterproofing techniques. Bearing in mind the importance of protecting the lift mechanism and equipment from water damage, how to construct a waterproof lift pit with the Master Builders Solutions waterproofing system essentially follows the same steps as other forms of other underground construction, although joint detailing is specific to the application.
According to NHBC Chapter 5.4: “Waterproofing design should be appropriate to the risk and generally assume exposure to a full height of water during the design life of the building. Where ‘Grade 3 protection’ (see Clause D7(a)) is required, and the below ground wall retains more than 600mm, measured from the lowest finished floor level, the waterproofing design should include a combination of two of the Types of waterproofing systems…” Combination systems include:
- Type A and Type B
- Type A and Type C
- Type B and Type C
The Master Builders Solutions Watertight system uses a combination of Type A and Type B waterproofing to create a lift pit that meets the requirements of BS 8102.
When building a lift pit, firstly form and blind the excavation. Place a horizontal layer of barrier membrane MasterSeal 754 and steel reinforcement mesh to the base, and cast the slab. On curing, you can then place the outer formwork for the walls, as well as affixing a swelling waterstop (MasterSeal 910) where the kicker joint will be formed. By placing MasterSeal 754 on the outer shutterwork, you will create a positive-side (external) barrier against the ingress of water.
Once the waterbars, steel reinforcement, and inner shuttering have been placed, held in position with tiebars (tie sleeves with MaterSeal 925 swelling rings should be used), the concrete walls can be poured. On curing, remove the formwork and finish the tieholdes with a swelling plug (MasterSeal 925), which is then covered with special mortar to prevent any weak spots that could allow water ingress. Finally, backfill the excavation.
With the Master Builders Solutions Watertight System, the concrete itself contains high-performance integral waterproofing, thanks the the addition of admixture MasterLife WP 799 during mixing. This means that the microscopic pores in the concrete are much reduced, helping to prevent the penetration of water through capillary action.
On the completion of correct placing, compaction and curing, this concrete solution provides a waterproof structure with minimum effect on the concrete’s appearance and texture. The end result is designed to perform in below-grade construction where the concrete is subjected to water pressure.
A CAD drawing of standard lift pit construction is available in our downloads section.