Let’s delve into the world of below-grade water defence and explore the differences between these two methods.
What Is Negative Waterproofing?
Negative side waterproofing, also known as internal waterproofing, tackles water intrusion from the inside of a structure. This method is typically used for existing structures where accessing the exterior for waterproofing is difficult or impossible.
Imagine a basement in a high-rise building—applying external waterproofing wouldn’t be feasible due to surrounding structures. In such cases, negative-side waterproofing becomes the solution.
Does Negative Side Waterproofing Work?
Yes, negative-side waterproofing can be effective in preventing water leaks. However, it’s essential to understand its limitations. While it protects the interior from water ingress, it allows moisture to enter the structure itself. This trapped moisture can damage the building materials over time. Additionally, adverse side waterproofing requires meticulous installation to ensure a complete seal and prevent future issues.
What Is the Difference Between Negative and Positive Waterproofing?
The key difference between positive and negative lies in the application location and how they address water intrusion. Here’s a deeper dive into their contrasting approaches:
| Aspect | Positive Side Waterproofing | Negative Side Waterproofing |
|---|---|---|
| Location | This method applies the waterproofing membrane on the exterior of the structure, directly against the soil. It creates a barrier between the soil and the building materials. | The membrane is applied on the inside walls of the basement or foundation, creating a secondary layer of defense from the interior. |
| Waterproofing Strategy | Acts as a first line of defense by intercepting water before it reaches the building components, offering comprehensive protection. | Addresses water that has already penetrated the building envelope, preventing further migration into interior spaces. |
| Impact on Building Materials | Prevents water from entering materials, extending foundation lifespan and reducing risks like cracking, mold, and efflorescence. | Allows some moisture to be trapped, which can lead to degradation over time without proper ventilation or drainage. |
| Durability and Maintenance | External membranes are robust and weather-resistant, but repairs may require excavation. | Indoor membranes are more vulnerable to wear and tear, and leaks may be harder to detect. |
| Choosing the Right Method | Best for new construction due to superior protection and durability. | Ideal for existing structures where exterior access is limited; professional consultation is recommended. |
| Overall Effectiveness | Provides proactive protection by keeping water out from the start. | Offers reactive protection by managing water that has already entered. |
Negative Waterproofing
Additional Considerations for Negative Pressure Waterproofing
While negative waterproofing offers a solution for existing structures, there are some additional factors to consider:
Material Selection Matters
- Due to the trapped moisture, a suitable waterproofing material for harmful applications must be chosen. Breathable membranes allow some moisture vapour to escape, reducing the risk of internal damage. There are two primary types of materials: one uses crystalline additives or expanding polymers to seal capillaries, and the other consists of cementitious coatings that fill gaps and solidify into a barrier, requiring manual pressure during application.
Drainage System
- A properly designed drainage system is vital, even with a good waterproofing membrane. This system collects any water that seeps through the structure and channels it away from the foundation, minimising its impact
Moisture Still Enters the Structure.
- Water cannot enter the building materials themselves when negative waterproofing is used, but it can stop it from getting to interior spaces.
- This retained moisture can eventually cause material deterioration, including corroded rebar or spalling concrete.
Meticulous Installation Required
- Any gaps or weak spots in the coating can allow water to seep through.
- Proper surface preparation and thorough application are critical to success.
Problems with Hydrostatic Pressure
- Water under pressure can put a lot of force on walls, particularly in tunnels or basements.
- Hydrostatic pressure, which rises with water depth (roughly 0.43 psi per foot of water), must be tolerated by the waterproofing system.
Aesthetic and Practical Advantages
- In addition to keeping interior spaces dry, some negative waterproofing products provide decorative finishes.
Maintenance
- Negative side waterproofing requires regular monitoring for signs of leaks or damage. Addressing any issues promptly helps maintain the integrity of the waterproofing system.
Advantages of Negative Waterproofing
Why Choose Negative-Side Waterproofing
1. Perfect for Structures That Are Already There
- Great for adding to buildings where getting to the outside is hard or not possible.
- Treating water that comes in from the inside keeps you from having to dig up the ground.
2. Cost-Effective
- Usually cheaper than positive waterproofing, especially for repairs.
- Needs less work and tools.
3. Simple to Use
- Can be used after the substrate has dried.
- Installation doesn’t need a lot of training.
4. Full View During Installation
- Technicians can see and fix problem areas directly by going inside.
- Easier to keep an eye on and fix over time.
5. Effective Management of Moisture
- Prevents water from entering the structure after it has already done so.
- Aids in preventing structural deterioration, mold, and mildew.
6. Adaptable Materials
- Capillaries and voids are sealed with cementitious coatings or penetrating acrylics.
- Decorative finishes can also improve the aesthetics of the interior.
When external treatment is impractical, negative waterproofing is frequently utilized in lift pits, tunnels, basements, and other below-grade locations. Do you need assistance creating a chart or blog post that directly compares it to positive waterproofing?
