Negative waterproofing, also known as below-grade waterproofing or tanking, is a method used to prevent the intrusion of water into below-ground structures such as basements, tunnels, or foundations. Unlike traditional waterproofing methods that address water infiltration from the positive side (exterior), negative waterproofing focuses on preventing water penetration from the negative side (interior) of the structure.

Negative waterproofing involves the application of waterproofing materials or systems to the interior surfaces of below-grade structures to create a barrier against water. Here are some key aspects of negative waterproofing:

1. Purpose: The primary purpose of negative waterproofing is to prevent water from seeping into below-grade structures, protecting them from moisture-related issues such as water damage, mold growth, and structural deterioration.

2. Application: Negative waterproofing typically involves applying liquid-applied membranes, cementitious coatings, or epoxy-based products directly onto the interior surfaces of the structure, such as walls and floors. These waterproofing materials create a barrier that prevents water from entering the structure.

3. Drainage Systems: In addition to the waterproofing barrier, negative waterproofing may include the installation of drainage systems to collect and redirect any water that does manage to infiltrate the structure. These systems can include sump pumps, interior drain tiles, or French drains.

4. Structural Considerations: Negative waterproofing is commonly used in situations where it is challenging or impractical to address water infiltration from the outside. It is important to note that negative waterproofing does not address the underlying causes of water intrusion, such as poor exterior drainage or hydrostatic pressure. Therefore, it is crucial to address these issues if they exist to mitigate potential water problems effectively.

5. Maintenance: Like any waterproofing system, negative waterproofing requires regular maintenance and inspection to ensure its effectiveness. Regular checks for cracks, deterioration, or damage to the waterproofing barrier should be carried out, and any necessary repairs or reapplication of waterproofing materials should be done promptly.

It is worth mentioning that while negative waterproofing can be an effective solution for preventing water intrusion from the interior side of a structure, it is generally recommended to address water issues at the source whenever possible. This can involve improving exterior drainage, sealing foundation cracks, or implementing other positive waterproofing measures to mitigate water infiltration before it reaches the interior surfaces.

Overall, negative waterproofing is an important technique for protecting below-grade structures from water damage and maintaining a dry and habitable environment. Consulting with a waterproofing professional or engineer is recommended to assess the specific requirements of your structure and determine the most suitable waterproofing approach.