(image source: Findlay Evans Waterproofing) Recent decades have seen the construction of an unprecedented number of multi storey apartment complexes.
Many of these buildings feature basements for underground car parking, storage, and utility areas.
However, an unfortunate consequence is a greater frequency of building defects. Of these, water leaks are one of the most common.
Consequences are serious. Leaking basements and foundations may compromise the structural integrity of the entire building. Without watertight footings & foundations, building structures have the potential to deteriorate rapidly. Water and moisture is the source of many problems in construction and is one of the biggest factors in corrosion of reinforcing steel in basements. Accordingly, below ground waterproofing is as important as the structural foundations supporting a building.
For some failed basement membranes, rectification may not be commercially viable or even possible to fix. Occasionally, poor waterproofing design, substandard product/s used and/or suboptimal installation are identified and rectified immediately. In most cases, however, problems are only identified where water ingress occurs down the track. Where this happens, extremely costly repairs are needed.
Concrete is not waterproof
Even where additives are applied, it is important to understand that concrete is not entirely waterproof.
Additives can take years to achieve their desired outcome. Concrete does crack and this provides potential weakness for water ingress.
At any rate, relying on the success of additives alone is concerning as their effectiveness is influenced by concrete movement and resultant cracks.
In addition, it is important to note that block work and masonry walls are porous. Even PVC type wall systems have the potential to leak at the base. It is also important to beware of vertical joins that can “pop open” during concrete infilling.
Then, there are concrete block systems which are built by stacking the blocks and filling the wall with concrete and steel reinforcing. These systems have several specific concerns in relation to water leaks. Often, builders try to waterproof these walls without first filling in all open joints. This is problematic as each block has a bevelled edge and creates a “V” at each join. These edges in most cases prevent any waterproof membrane being applied properly.
One solution to this challenge is a “bagged” wall which is constructed by using a slurry of sand/cement to fill all the divots first. This provides a prepared surface which is now ideal for a membrane to be correctly applied. A sheet membrane can be applied over these joints without bagging, but the overlapped joints can break and create miro ports for water ingress into the wall. The termination at the base of wall is tricky to seal as well and waterproofing may fail.
Damp proofing vs Waterproofing
When designing and applying waterproofing systems, it is important to understand the difference between damp proofing and waterproofing.
Damp proofing is intended to keep soil moisture out, but not liquid water, which may enter via penetrations, gaps, cracks, and holes.
By contrast, waterproofing keeps out both water AND moisture. A quality waterproofing system is therefore required needed as part of structural design in order to permanently stop water moisture and prevent water vapor from entering below ground structures.
This is important as the benefits of full waterproofing far outweigh those of simple damp proofing over the building lifespan. This is despite the fact that the upfront cost for waterproofing is significantly higher compared with that for damp proofing.
Below Ground Waterproofing – Design & Planning
For new construction several steps are needed to ensure water ingress does not occur in basements.
- During construction of the slab floor / wall zone – these areas require a water stop for either tilt panels or block work.
- Crystalline growth should be included compound in the concrete pour of walls or as a fill-in for block work.
- Once walls are constructed, ‘tanking’ should be applied with quality waterproofing membrane.
- Quality implies that a below ground waterproofing system is expected to last the lifetime of the building.
- Membranes should be protected by installing a suitable barrierprior to backfilling.
- Effective water management should be provided via good drainage. There are many design options for this
- Sufficient ventilation must be allowed for.
Below Ground Waterproofing – System Installation
Waterproofing membrane systems are available as either post-applied or pre-applied products for use in either positive-side, negative-side, or blind-side applications.
- Positive-side waterproofing systems are post-applied to the surface of the element that is directly exposed to moisture, typically the exterior side of the foundation wall.
- Negative-side waterproofing systems are post-applied to the surface of the element opposite the surface exposed to moisture, typically the interior of the foundation wall.
- Blind-side waterproofing systems are pre-applied to the area where the concrete element will be placed that is directly exposed to moisture.
Positive-side systems are available in numerous materials and forms. Negative systems are generally limited to cementitious systems.
Positive Below Ground Waterproofing Installation – General Guidelines
At the time of construction, positive below ground tanking (exterior wall) should be applied to the foundation and/or retaining walls.
Waterproofing should be applied a minimum of 50 mm above the finished grade, and then applied to a point 300mm below the top surface of the interior slab (base of footing) on a constant grade.
Weather & Waterproofing
Weather plays a large part in the success or otherwise with waterproofing installation. This needs to be appreciated and understood.
Planning and timing below ground waterproofing installation around climatic conditions is problematic as construction scheduling rarely allows. As a result, installation is often applied at a time when inclement weather will adversely affect the below ground waterproofing system.
Climatic conditions will affect the foundation as wet soil beneath a basement/foundation can swell causing loss of strength.
Generally, it is very difficult to achieve successful waterproofing during wet seasons.
Keeping Basements Dry
Did you know that waterproofing represents 1.8 percent of a building’s construction costs, but accounts for a whopping 83 percent of building defect complaints?
There is currently no below ground waterproofing standard in Australia. Instead, best practices and performance solutions are the norm for designing waterproof structures today.
Currently there is a direction to adopt the British Standards with amendments for Australian conditions.
Furthermore, the need for “dry” basement standards and waterproofing has become even more important with the growing use of living space blow ground such as home theatres .
Exterior basement waterproofing systems should be intended to resist water and accompanied by a water management system that will remove ground water away for the structure as best as possible.
In some cases, a secondary water collection/management system can be installed on the inside or the negative side of a basement.
Overall, when it comes to below ground structures, we need to eliminate the possibility of water penetration for the duration of the life of the structure.
Article by Paul Evans ,President, Australian Institute of Waterproofing (AIW) , Managing/Director Findlay- Evans Waterproofing
The Australian Institute of Waterproofing (AIW) is a voluntary group of contractors and manufacturers offering their own time to be a voice for waterproofers and better the industry in general across Australia.
As always, the AIW is here to help. We have a strong team of qualified and dedicated members who care about the industry.
Our Team is currently working to provide Below Ground Waterproofing guidelines for Australia.
The AIW has representation in most states and with members across Australia.
Registered Victorian Building Practitioner (RBP)
Building Practitioners Board License CBU-4077 & DBU-7983
Master Builders Association Victoria (MBAV) Specialist Contractor – License 094507
Telephone: (03) 8812 2918
Australian Institute of Waterproofing (AIW)
Address: 155 Barkly Ave Burnley Vic 3121
PH: 1300 249 466