Below-Grade Waterproofing: Gravity Feed and Pressure Injection Applications


CGI Northeast’s concrete gel injection waterproofing system is best known for its ability to eliminate water intrusion using a two-component hydrophilic resin system in below-grade structures without costly and disruptive exterior excavation common with traditional waterproofing applications. As a result of its beneficial methodology, property owners and managers can leverage CGI’s technology to effectively tackle damaging waterproofing issues in creative ways. Today, we will explore two of CGI’s unique applications – its gravity feed waterproofing application, along with its pressure injection waterproofing application.

CGI’s gravity feed waterproofing application incorporates feeding the 2 water-like viscosity liquid components within the cleaned out expansion joints to create a gel barrier, followed by the application of new urethane caulking.

Typically, a vaulted sidewalk structure is comprised of a horizontal structural slab with a top-side waterproofing membrane and a walkway slab on top of the structural slab. The structure typically has expansion joints installed every 20 ft. or 4 flags apart, which are prone to deterioration as a result of freeze–thaw cycles and pedestrian traffic, giving way to rainwater to enter from the compromised membrane locations on top of the structural slab.


CGI’s gravity feed waterproofing application begins with mechanics removing the deteriorated old caulking and debris from within these joints, allowing for two liquid components to be gravity fed at a longer setting time. As a result of the two components’ water like viscosity, the combined solution chases through the opened joints like rainwater, allowing the resulting gel to form a band where the membrane was compromised. Subsequently, backer rod is inserted within the joints followed by caulking with the appropriate urethane sealant. In the case of a granite slab, where the top sidewalk expansion joint runs to the cellar underside of the granite, CGI’s mechanics insert oakum within the joint to act as a form, which then allows the gravity feeding waterproofing method to take action utilizing new urethane caulking.

The second application we’ll touch upon is CGI’s pressure injection waterproofing method through the underside of vaulted overhead horizontal slabs in sidewalks and plazas. This system can be implemented through the underside of the structural sidewalk slab through defined water intrusive cracks and joints.

A vaulted plaza location with sidewalk level pavers and/or planters is constructed in the same manner as a vaulted sidewalk (as described above), with the addition of soil on top of this membrane for planters/landscaping or a mud-set mortar for pavers. In this scenario, CGI’s mechanics drill and inject through the underside of the concrete horizontal structural through the water entry points from the cellar ceiling slab below, allowing the two liquid components to seek the sources of water entry and seal them with the resulting gel. Using this application, the pavers and/or planters need not be removed, avoiding the need to repair or re-install a new top-side waterproofing membrane, which can be a big expense.

With the CGI waterproofing system, the mechanics never need to drill to the exterior top side, which would puncture and compromise the existing waterproofing membrane. This methodology is unlike grout injection with ports, where the grout injection holes are drilled all the way to the exterior side for the grout to form a foam curtain. Also grout injection does not have the water-like viscosity that CGI offers and cannot be utilized in this type of application.

For more info please visit cginortheast.com


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