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Below-Grade Waterproofing Membranes, Primers, and Accessories

Below-grade structural waterproofing is necessary for preventing costly water damage to any part of the building below ground level. Appropriate waterproofing products and systems are needed to protect below-grade concrete structures like basements, underground parking, and foundation walls from water infiltration.

Polyglass’ range of structural waterproofing systems includes pre- and post-applied waterproofing membranes, and accessories for horizontal and vertical applications. Our solutions cover a wide range of technologies to meet varying designs and specifications for below-grade foundations, split slabs, and elevated plaza deck applications.

Explore our below-grade waterproofing products below.

What is a Building Envelope?

The building envelope comprises all the materials that make up the wall assemblies, roof systems, exterior doors, windows, and below-grade components (horizontal slabs and foundation walls) that physically separate and protect a building’s interior environment from external environmental forces and conditions.

A building’s enclosure helps to balance and control its internal environment, keeping occupants safe and comfortable. Inadequate ‘sealing’ of the building envelope leads to performance issues (decreased efficiencies) and compromises a building’s structural integrity.

Why Does the Below-Grade Structure Need Waterproofing?

Below-grade building structures are particularly susceptible to water and moisture damage if not appropriately waterproofed during construction.

Water infiltration can weaken below-grade structures by corroding reinforcing steel. For example, dissolved salts and chemicals found in water can have a degrading effect on concrete foundation slabs, walls, and steel.

Polyglass’ below-grade waterproofing products and systems have been uniquely designed to prevent water infiltration and lateral water migration below grade. They are also highly resistant to harmful chemicals and natural salts found in ground and surface water.

Waterproofing Membranes for Below-Grade Applications

Polyglass’ post-and pre-applied waterproofing membranes are suitable for horizontal underslab and vertical blindside applications.

Our below-grade waterproofing membranes use high-density polyethylene (HDPE) or a combination of woven and nonwoven polypropylene (PP) geotextile fabrics and sodium bentonite clay.

HDPE is an ideal waterproofing material for below-grade structures. It offers a high strength-to-density ratio, resistance to naturally-occurring chemicals found in soil, and is impervious to water, acids, solvents, and common chemicals. Sodium bentonite expands when wet to form a single waterproofing membrane, while PP is known for its chemical resistance, elasticity, toughness, and fatigue resistance.

Solvent and Water-Based Waterproofing Primers

Water- or solvent-based adhesive primers like Mapeprime™ S710 and Mapeprime™ 720 W are used for improved adhesion of Polyglass’ self-adhered waterproofing membranes to a range of prepared substrates.

Below-Grade Waterproofing Accessories

Various Polyglass accessories are available for below-grade waterproofing, including

  • Liquid membrane for detailing of both pre and post-applied systems, such as terminations and penetrations through slabs and walls.
  • Pressure-sensitive detail tape that bonds to pre-applied waterproofing membranes, ensuring watertight details.
  • Bentonite granules for detailing with PP waterproofing membranes.
  • Drainage mats or boards help channel water away from installed waterproofing systems and relieve backfill and hydrostatic pressure.

Related Resources

Frequently Asked Questions

  • What does below-grade waterproofing mean?

    Below-grade waterproofing refers to protecting underground surfaces or building structures to prevent water penetration and protect them from water-related damage. Standing or resting water, often found in the soil surrounding a building’s foundation, exerts hydrostatic pressure against foundation or basement walls and below-grade structures.

    This hydrostatic water pressure forces water into existing cracks, which then moves (or migrates) further into a building and causes additional damage. Waterproofing systems and solutions, like Polyglass’ fully-bonded membranes, create a watertight seal that protects below-grade structures from hydrostatic pressure and lateral water migration.

  • What is the best below-grade waterproofing?

    In reality, a variety of interacting waterproofing components are needed to seal the building envelope sufficiently from water damage, including:

    • Waterproofing membranes
    • Protection, drainage, and insulation courses
    • Water stops
    • Expansion and control joints
    • Flashings and counter flashings

    The best below-grade waterproofing materials and systems for a project depend on its design, budget, site conditions, and more. Below-grade waterproofing materials and systems can be post- or pre-applied depending on the nature of the job site.

    If existing below-ground structures can be readily accessed and waterproofed from the outside, then post-applied waterproofing products are ideal. If site conditions don’t allow access to below-grade foundation walls, then pre-applied membranes would be utilized against the support of excavation.

  • Why Polyglass?

    Polyglass® is an ISO 9001:2015 Certified, leading manufacturer of modified bitumen roofing and waterproofing membranes and roof coatings for low- and steep-slope applications. We are an industry leader in self-adhered underlayments that are specially designed to help contractors save time and labor costs.

    Utilizing the most technologically advanced manufacturing process in the industry, Polyglass operates six state-of-the-art manufacturing facilities — five in North America and one in Italy that serves all of Europe.

    As a company that prides itself in innovative and quality roofing products that exceed the needs and expectations of its customers all around the world, we offer roofing contractors the following benefits:

    • An extensive line of underlayments and other roofing products that allow for custom-designed solutions for unique construction challenges and environmental conditions
    • Outstanding technical support and project assistance
    • The most trusted warranties in the industry
    • A registered contractor program and a wide array of contractor resources, including instructional videos to Polyschool courses.
    • The ability to earn points and redeem prizes for every Polyglass purchase with QRewards

    Evolving through innovation, Polyglass offers high-performance and exceptional quality Building Envelope Solutions. Our expert team is here to help you choose the best products and solutions for your next below-grade waterproofing project. Get in touch today.

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