CASE STUDY: BLINDSIDE WATERPROOFING

In most instances, traditional foundations are possible. However, some factors may justify preapplied waterproofing. Blindside foundations are mostly used when the project is located in a high-density urban area where the generally restricted space does not allow for the excavation of an open trench outside of the foundation perimeter. Usually, this type of excavation is found in urban environments with underground parking. For this type of foundation, the waterproofing product must be installed on the outside of the foundation. Because these sites usually have several underground levels and may have other quirks adding complication to waterproofing membrane installation, it is essential to use high-performance products, be properly trained and have the necessary technical support in order to respect the system integrity.

The $1.4 billion Atlantis Resort & Residences in Dubai was built using SBS-modified bitumen blindside waterproofing membrane.

In the case of the Royal Atlantis Resort & Residences on the famous Palm Jumeirah Island in Dubai, United Arab Emirates, proximity to both urban structures and bodies of water made blindside waterproofing a necessity. This project consisted of substructure waterproofing for a $1.4 billion, 46-story resort consisting of 791 guest rooms and suites, and 230 luxury residences. The buildings include restaurants, retail and entertainment, as well as a swimming pool 90 meters above the ground. The project is located on the crescent of the man-made palm-shaped island and is adjacent to the existing Atlantis resort.

A high-performance SBS-modified bitumen blindside waterproofing membrane system with either composite or polyester reinforcement (depending on which product variant was chosen for specific applications) was selected for the project in large part because it demonstrates the best resistance to hydrostatic pressure in the industry by a wide margin. This was especially important with the Royal Atlantis Resort & Residences project, as it is located near a large watercourse (the Persian Gulf) and had to resist extremely high hydrostatic pressure if water infiltration was to be avoided.

The specified blindside waterproofing system was designed to protect infrastructure against leaks that might occur between the concrete walls of buildings affected by the waterproofing operation. While the concrete cures, the surface of the waterproofing system membranes clings to the structural concrete, ensuring total adherence to eliminate the risk of lateral water migration between the waterproofing membrane and the foundation wall.

The installation team worked to customize all previously issued and approved details on the Royal Atlantis Resort & Residences in accordance with the blindside waterproofing system, which included tying in preapplied SBS-modified bitumen blindside waterproofing materials with post-applied thermofusible waterproofing membrane all throughout an application area that included different levels of elevations, construction joints and expansion joints. In the end, 250,000 square-meters of SBS-modified bitumen product was installed in line with the specified construction schedule.

Not every blindside waterproofing endeavor will be as large-scale as the Atlantis project, but this example shows how blindside waterproofing can protect everything from the average subterranean parking garage to even the most grandiose of buildings with specialized construction requirements.

With negative-side waterproofing, membranes are installed on the interior side of the wall, preventing moisture from penetrating inside the space, but potentially allowing damage within the wall.

There is one additional form of below-grade waterproofing to know, as well: negative-side waterproofing. As you might guess from the name, negative-side waterproofing protects the surface opposite the side of applied hydrostatic pressure (e.g., the inside of a basement wall). Negative-side waterproofing keeps water from entering an occupied space and is applied to what is known as the dry face. Negative-side waterproofing is primarily used for water-holding purposes (preventing water from entering a space), but it does not prevent the water from entering the substrate (wall).

The main advantage of negative-side waterproofing is that it is accessible after installation for repairs or updates. Also, since the negative (interior) side of walls tends to be more accessible, it is easier to identify leak locations than with positive-side systems.

The fact that negative-side waterproofing allows moisture into the substrate is generally seen as a disadvantage, however. While moisture promotes active curing of the concrete substrate, it also contributes to the corrosion of the concrete and steel reinforcements from the groundwater and chemicals. The constant presence of moisture can also lead to mold growth or damage to interrelated building elements like floors or windows. This type of membrane does not protect against the effects of the freeze-thaw cycle and can only be used on cementitious systems. Additionally, if the building moves or cracks over time, additional negative-side waterproofing products may need to be added to close new gaps.

The materials used for negative-side waterproofing must be able to withstand hydrostatic pressure. Prefabricated membrane systems are typically installed in negative-side waterproofing applications via epoxy or urethane injections, cementitious coatings, metallic mineral application or crystalline application.

Since the goal of waterproofing is to protect both structures and the content within, but negative-side waterproofing does not necessarily protect the structure itself, negative-side waterproofing should generally be looked at as a temporary solution or problem-solving method that is mainly considered only if the positive-side waterproofing has failed or could not feasibly be installed in the first place.

Water Management & Protection

Keeping water out is one challenge; managing water and protecting newly installed below-grade waterproofing assemblies is another. This is why we also install protective layers, drainage layers and waterstops.

Protective layers, as their name implies, protect below-grade membranes from damage. This damage can either occur from backfill or consecutive trades. Depending on the membrane, common materials used in protective layers include insulation, asphaltic boards or an additional layer of HDPE. In some cases, layers serve dual purposes, such as insulation and drainage layers.

Drainage layers, alternatively, assist in the relief of hydrostatic head pressure and prolong the membrane life. Proper design means having the least possible amount of water reach the membrane, and water management is highly recommended in all below-grade assemblies. These panels are typically impact-resistant, dimpled plastic attached to a woven geotextile fabric, and they channel water away from the membrane.

Almost all below-grade waterproofing projects will have either a protection layer (board) to protect against possible damage from backfill operations or a drainage solution to manage the water away from the waterproofing membrane. Some drainage solutions can protect both the membrane and manage the water.

Waterstops provide a final level of protection for the building, existing within concrete sections, especially joints. These premanufactured joint seals are often comprised of PVC or chloroprene rubber that must be fused together, bentonite clay that expands when wet or hydrophobic injectable expanding grouts.

Causes of Waterproofing Failure

As is often the case with construction quality, the “devil is in the details” when it comes to effective below-grade waterproofing. It does not matter how great a waterproofing product is if it is not installed correctly—it can instantly perform worse than the worst waterproofing product in the world.

Improper Flashing & Detailing

Gaps in the integrity of the waterproofing due to incorrect detailing or damage from other trades are a leading cause for failure. The picture on the next page shows one example: rather than use the proper installation techniques, the contractors took it upon themselves to assure this elevator pit’s preapplied waterproofing was snug to the forms by using a staple gun to shoot staples through the modified bitumen membrane and into the wood forms. This created approximately 30 penetrations through the membrane that had to be detailed properly after the staples were removed (which you can see on the right). The correct repair procedure in this case was a patch over all the holes once the staples were removed … which added up to out-of-scope costs in excess of $10,000 once labor and materials were factored in.

Improper installation techniques can add up to costly fixes that are not within the original scope of projects.