Precast concrete storm water tank

How to keep plot foundations waterproof November 29th 2018, by Ian Lishman

Think of foundations and your mind might only go as far as strip or pad foundations used on low-rise construction projects, especially housing. But foundations are also load-bearing solutions that sit deeper in the ground, and can even encompass basement structures.

When can water be a problem for foundations?

The loads imposed by a building, combined with the condition of the ground, dictates how deep the foundations have to go. Deeper foundations are likely to mean the height of the water table becomes a greater concern. But particularly wet ground can be an issue on a project of any scale.

Ground that is dry, or appears dry, may not seem like it could cause a problem, but prolonged rain or a short period of extreme weather could quickly change the picture. There is a big difference between designing damp proofing measures, which help combat the movement of water vapour, and waterproofing measures capable of resisting liquid water.

Hydrostatic pressure caused by ground water or intense rainfall can force liquid water into gaps and cracks in the structure, or into the cellular structure of materials themselves. The likely result is damage to the foundation and possible water ingress to the building.

What foundation waterproofing options are there?

Foundation waterproofing should be planned for from an early stage and specified appropriately, but it is still helpful to work with an experienced foundations contractor who can respond to site conditions and contribute to the decision making process as works progress.

That experience extends to understanding the mix of concrete used and how long a foundation needs to dry, to avoid trapping more moisture than is necessary within the concrete. Even on a dry day, if humidity is high, concrete can take in moisture from the air.

Waterproofing techniques may be referred to as tanking, and can be applied externally or internally. Internal tanking leaves the structure open to possible water ingress and relies on effective drainage within the building envelope to keep it from reaching the habitable spaces.

External waterproofing/tanking measures protect the structure and keep water in the ground. There are different types of external waterproofing, each offering different features and benefits depending on the specific demands of a given project. Plastic-based or bitumen-based products may be liquid applied, a membrane, or a self-adhesive membrane with a protection board. Some products can be installed in already-wet conditions, or react to water and ‘self heal’ to form an effective barrier.

How can ground water be managed?

Implementing measures to keep water away from the building is part of an overall ‘waterproofing strategy’, not just something to be considered at the groundworks stage. Effective roof drainage and well-maintained gutters that discharge through elongated outlets can stop excess water entering the ground around a building and putting pressure on foundations.

Another tactic might be to employ the use of a french drain. A pipe is laid in a trench around the building, directing water away from the building and reducing water pressure on the below-ground structure. French drains need careful design to avoid drying the ground more than expected, but are a legitimate tactic.

About FACE

For nearly two decades, FACE have delivered high quality civil engineering works on projects of all sizes. Our new turnkey service allows housing developers, whether small or large, to work with us and build a project-specific package of services that FACE then delivers.

The package can include highway works carried out under a section 278 agreement, drainage construction and groundworks. Acting as a single point of contact for multiple aspects of the infrastructure means we can offer improved coordination of works and minimise potential delays.

Find out more and enquire about our turnkey packages here.