Installing Waterproofing for Below-Grade Parking

Waterproofing is an essential aspect of constructing below-grade parking structures. These structures are prone to water infiltration, which can cause numerous issues such as concrete deterioration, corrosion of steel reinforcement, and damage to vehicles or stored items. To prevent these problems, proper waterproofing techniques must be employed during the construction phase. In this article, we will explore the installation techniques for waterproofing below-grade parking structures.

Importance of Waterproofing Below-Grade Parking Structures

Before delving into the installation techniques, it is crucial to understand why waterproofing is essential for below-grade parking structures. These structures are typically underground or partially underground, making them vulnerable to water infiltration from the surrounding soil. Without proper waterproofing measures, water can seep through cracks, joints, or porous concrete, leading to a range of issues.

Some of the potential problems associated with inadequate waterproofing include:

  1. Concrete deterioration: Water infiltration can cause concrete to deteriorate over time, leading to structural damage and compromising the integrity of the parking structure.
  2. Corrosion of steel reinforcement: The presence of water can initiate or accelerate the corrosion process of steel reinforcement, which weakens the structure.
  3. Mold and mildew growth: Moisture provides an ideal environment for mold and mildew to thrive. Not only can this lead to unpleasant odors, but it can also adversely affect the air quality within the parking structure.
  4. Damage to vehicles or stored items: Water leaks can damage vehicles and other items stored within the parking structure, resulting in expensive Repairs or replacement costs.

To avoid these issues, below-grade parking structures must undergo proper waterproofing during construction.

Installation Techniques for Waterproofing Below-Grade Parking Structures

When it comes to waterproofing below-grade parking structures, several techniques and materials can be utilized. Here are some commonly employed installation techniques:

1. Sheet Membrane Waterproofing

Sheet membrane waterproofing is one of the most common techniques used for below-grade structures. It involves the installation of flexible, rubberized sheets onto the concrete surface. These sheets act as a barrier, preventing water from penetrating the structure.

Steps involved in sheet membrane waterproofing include:

  • Surface Preparation: The concrete surface must be thoroughly cleaned and free from any debris or contaminants.
  • Primer Application: A primer is applied to enhance the adhesion between the concrete and the membrane.
  • Membrane Installation: The sheets are installed onto the primed surface, ensuring proper overlap and protection of vulnerable areas such as joints and corners.
  • Seam and Joint Sealing: The seams and joints between the sheets are sealed using specialized products to create a continuous waterproof barrier.
  • Protection Layer: Depending on the project requirements, a protection layer may be added to shield the membrane from damage during backfilling or construction activities.

2. Liquid Applied Waterproofing

Liquid applied waterproofing involves applying a liquid coating directly onto the concrete surface. This technique offers flexibility and can adhere to irregular surfaces and complex designs, making it ideal for below-grade parking structures.

Steps involved in liquid applied waterproofing include:

  • Surface Preparation: Similar to sheet membrane waterproofing, the concrete surface must be clean and free from debris.
  • Priming: A primer is applied to enhance adhesion between the concrete and the liquid membrane.
  • Application of Liquid Membrane: The liquid membrane is applied using various methods such as spray, trowel, or roller, ensuring even coverage and proper thickness.
  • Curing and Protection: The applied membrane must undergo a curing process to attain its full waterproofing properties. Additionally, a protective layer may be added to safeguard the membrane during subsequent construction activities.

3. Bentonite Waterproofing

Bentonite waterproofing relies on the unique properties of bentonite clay to create a watertight barrier. When hydrated, bentonite clay forms a dense, impermeable layer that prevents water from infiltrating the structure.

Steps involved in Bentonite waterproofing include:

  • Surface Preparation: The concrete surface must be clean and free from any loose particles or contaminants.
  • Hydration of Bentonite: Bentonite clay is hydrated on-site and applied onto the prepared surface, ensuring proper coverage and compaction.
  • Overburden Placement: To protect the bentonite layer from damage, an overburden material such as soil or sand is placed over the top.
  • Proper Drainage System: For effective water management, a reliable drainage system must be installed alongside bentonite waterproofing to prevent the buildup of hydrostatic pressure.


Q: What are the benefits of sheet membrane waterproofing over other techniques?

Sheet membrane waterproofing offers excellent flexibility, making it suitable for irregular surfaces and complex designs. It also provides a physical barrier against water infiltration and is relatively easy to install.

Q: Which waterproofing technique is best for below-grade parking structures with heavy traffic?

Liquid applied waterproofing is often recommended for below-grade parking structures with heavy traffic. Its ability to adhere to irregular surfaces and withstand constant movement makes it ideal for high-traffic areas.

Q: Can waterproofing be applied to existing below-grade parking structures?

Yes, waterproofing can be applied to existing below-grade parking structures. However, the process may vary depending on the condition of the structure and the chosen waterproofing technique. Consulting a professional waterproofing Contractor is highly recommended to ensure the best approach.


Waterproofing below-grade parking structures is vital to prevent water infiltration, which can lead to various issues such as concrete deterioration, steel reinforcement corrosion, and costly damage to vehicles or stored items. By employing techniques such as sheet membrane waterproofing, liquid applied waterproofing, or bentonite waterproofing, construction professionals can ensure the longevity and structural integrity of below-grade parking structures. Remember, proper installation techniques and materials are key to effective waterproofing.

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