Blindside Waterproofing – just one chance to get it right

Background 

Blindside waterproofing – or pre-applied waterproofing – is a below-grade waterproofing system applied before building construction. Examples include installations against shoring systems and existing buildings and include most mat foundations or slab-on-grade conditions. This type of waterproofing application is necessary when the exterior side of the foundation wall is not feasible to expose, due to project location restrictions.

Challenges

Blindside waterproofing presents challenges with sequencing, tie-ins and protection from other trades. After site preparation work, waterproofing contractors are the first trade on-site. Their work is followed by several more, including foundation, concrete, steel reinforcement, utility, and other contractors. Inefficient coordination with any of them can result in discontinuous waterproofing, a damaged membrane, or lack of tie-in for adjacent areas. When it comes to blindside waterproofing, there is only one chance to get it right, and following the considerations outlined below can help you avoid trouble areas in the future.

Considerations

Design professionals and contractors have the opportunity and responsibility to influence blindside waterproofing installation success by considering areas such as:

Geotechnical Investigation

• A Geotechnical Report for soil or groundwater contaminants should be forwarded to the waterproofing manufacturer to confirm that the product specified is suitable. Different blindside materials may have different chemical resistance properties; reviewing contaminants lets the manufacturer approve or recommend the appropriate material based on site contaminants and concentrations.
• Boring samples showing groundwater elevations should also be presented to the waterproofing manufacturer to confirm proper product selection. Again, different materials may have different properties, including how much hydrostatic pressure they can resist. Reviewing groundwater elevations lets the manufacturer approve or recommend appropriate materials, and it gives the design professional the ability to specify different compatible materials or detailing at various elevations.

Quality Assurance

• The pre-installation meeting should include other trades that could influence the waterproofing integrity. Trades that work on, are adjacent to, or are above the waterproofing should all participate. This will ensure that the waterproofing is protected and continuous, and the work between all trades is properly coordinated and sequenced.
• “First Point of Verification” is an in-place mockup for the first time each construction phase relevant to waterproofing is performed. For example, the means and methods to erect and remove a bulkhead/pour stop/header may be discussed and agreed to during the pre-Installation conference. However, until this work is done, waterproofing contractors cannot verify that the continuous waterproofing is either intact or compromised.
• “Hold-Points” for blindside waterproofing are ongoing verification or inspection stages to ensure that the installation quality meets the specification and manufacturer requirements. The following inspection stages performed by a waterproofing manufacturer-approved consultant must be discussed, understood and agreed to at the pre-installation conference:
  • After substrate preparation, but before waterproofing system installation
  • After waterproofing system installation, but before steel placement
  • After steel placement, but before concrete placement
  • Periodically during concrete placement
  • Any other work that could compromise the waterproofing, such as:
    • During installation and removal of bulkheads, pour-stops, etc.
    • During welding/cutting operations
    • After excavation at grade

Transitions & Tie-Ins

• It is imperative to properly sequence work to help ensure continuous waterproofing; this includes sequencing how the blindside waterproofing transitions at grade with the rest of the building envelope.
• Dissimilar materials and/or different manufacturers may create an incompatible tie-in; for example, between the blindside waterproofing and the air barrier. These transitions may even be performed by different contactors, creating an additional layer of complexity.
• Specifications typically cross-reference each other, but due diligence in specifying compatible materials will better ensure that these transitions and tie-ins are properly designed. If materials are submitted and approved as alternates, the manufacturers for both the blindside waterproofing and air barrier (for the example above) should be consulted.

“You only get one chance to get it right” once the blindside waterproofing is no longer accessible. Designers and contractors have many opportunities to get it right prior to concealment of the membrane through proper planning, sequencing and coordinating the work with the General Contractor and relevant trades.

Schedule a meeting with your Henry advisor today!