The Economics of Quality Assurance in Waterproofing
- John D'Annunzio
- Jun 16, 2018
- 5 min read
Quality assurance procedures identify the requirements of the completed waterproofing project and set the quality levels that must be met for project approval. Quality assurance can be implemented at every phase in the waterproofing construction process.
At the design phase, quality assurance can ensure that the design meets the code requirements and that the materials specified can are accurate for the site-specific conditions. Review of site testing – i.e. soil conditions, water table level, presence of hydrostatic pressure, chemicals – have an impact on the type of materials required. Having a qualified waterproofing expert review the initial project design documents can provide cost savings by eliminating delays in construction from change orders and potential material failures.
At the waterproofing application phase quality assurance is monitored by an on-site quality control inspector. The role of the quality control inspector is to verify that the work and materials used satisfy the applicable standards as specified within the quality assurance process. The quality control process may also include on-site testing to ensure application is in accordance with the project requirements. The quality control inspector can also serve as a liaison between the Owner and the project participants – Designer, Project Manager, Applicators – and serve as part of the team that approves modifications to design, materials, and application methods as on-site conditions arise.
The Cost-Benefit Analysis of waterproofing quality assurance depends on the complexity and size of the project as well as the value of the asset to be protected. The waterproofing system is one of the few major building components where the material is completely covered and there is no immediate access for repairs. If a leak occurs on a waterproofing project, the cost of excavation and/or coverings could exceed the cost of the initial application. The reason for this is that in below-grade waterproofing the cost of excavation far exceeds the initial cost of application. For instance, an opening may be located deep below the surface requiring removal of overburden, such as trees, concrete, landscaping, followed by excavation of soil to reach the point of moisture infiltration. Once the repair is made everything must be put back.
Unlike the interior, the roof, or the facade: you only have one chance to do waterproofing right.
Unlike the interior, the roof, or the facade: you only have one chance to do waterproofing right. Taking that into consideration, the quality assurance process can be viewed as an insurance policy. The cost of quality assurance may be less than the cost of excavation required to repair one leak. Most manufacturers warranties do not cover the cost of excavation. Studies indicate that projects that have quality assurance in place experience fewer call backs than projects without quality assurance.
In the past thirty years I have conducted evaluations on dozens of waterproofing failures. The causes of these failures ranged from improper design, improper material selection and improper workmanship. The most memorable failures were the instances where the waterproofing membrane was never applied prior to backfill. Imagine the look on the owner’s face when they are informed that the building is leaking because the waterproofing application that they paid for never occurred.
Although it is easy to diagnosis the problem, the resolution is extremely costly. One of the cases occurred at a runway of a major U.S. airport. The runway was applied over an underground structure that housed the computer terminal for the airport. The runway concrete – extremely thick – had to be removed, the waterproofing system had to be applied and the runway concrete – extremely thick – had to be repoured. This is an extreme case; however, it is not all that uncommon.
Waterproofing is applied in phases as construction of walls and plaza decks are installed. There may be extended periods of time between certain waterproofing applications and completion. For instance, waterproofing of below-grade walls is typically done in 6 to 8- foot increments from the bottom to the top. The initial section is finished, the site is backfilled, and the waterproofing applicator uses the backfill as a scaffolding to complete the next increment. This process is continued until the full wall is waterproofed. This process could continue over an extended period because the waterproofing applicator relies on the pour schedule and the backfilling process.
What happens when you do this....
Then this happens...
There have been instances where the backfill is applied prior to the completion of the membrane application. At least once a year I receive a call to investigate a waterproofing leak and the result is that membrane was not applied in a section that has been backfilled. If the owner is fortunate the area backfilled prematurely is the top lift and only minor excavation is required to apply the membrane.
I have also had a couple cases where the membrane was purposely not set in designated areas to accommodate future openings for wall equipment penetrations. When the wall equipment was installed it was found that the designated openings were too large so the actual cuts to the wall decreased in size. Unfortunately, no one alerted the waterproofing contractor, so the area was backfilled without the application of the waterproofing membrane at the perimeter of the opening.
The previously mentioned failures were the exception – most waterproofing failures occur where the membrane has been installed – albeit improperly. The most common cause of waterproofing failures is improper workmanship. To a large extent the problems can be traced to the changes in materials and application methods that we have experienced in the past decade. Most of materials used today have ambient temperature constraints that limit their use. If the material is applied when it is too hot or too cold or if they are not properly stored in warm areas prior to use, the chance of failure increases.
We now use a substantial amount of cold applied materials for membrane adhesion – the most important element of the waterproofing membrane application. If these materials are not applied at the manufacturer required coverage rates – too much or too little – the chance of failure increases. The chance of failure also increases if the adhesives do not cure – or cure too quickly – prior to membrane application.
The improper use of materials is also a concern. With the increase in popularity of ‘garden type’, ‘living’ or ‘green’ roof applications in the early 2000s, a significant number of roof system manufacturers began to identify their roof membranes as waterproofing membranes. These types of materials may be suited for some waterproofing applications – such as horizontal plaza decks – they are not suited for most other waterproofing applications. The reason for this is the conditions that waterproofing membranes are to perform under (literally) are vastly different than requirements for roofs.
The first and foremost difference is that waterproofing materials may be exposed to continual standing water for large periods of time, whereas most roof materials cannot be exposed to ponding water for more than 48 to 72 hours. Waterproofing membranes should have a water absorption rate of less than 5% - some roofing materials have rates more than 10%. Waterproofing materials are also exposed to hydrostatic pressure, soil conditions, and numerous chemicals that roof materials cannot be exposed too. Nevertheless, roof materials are often used in waterproofing and the chance of failure increases.