Negative-side waterproofing is the act of applying waterproofing materials to the negative, or dry side, a.k.a. the interior side of your building’s foundation or wall. Building owners will often fill the maximum amount of property square footage possible with their new structure, leaving little room on the exterior of their structure’s property for the amount of excavating needed to do positive-side (or exterior) waterproofing. In another scenario, maybe you have a leak in a deep elevator pit. Perhaps it’s located in a downtown Toronto building where there is no way you can access that building’s exterior to waterproof it without digging up an entire city block and disrupting busy street traffic to make it happen. Or for some reason, the continuity to access the exterior side of your building is impossible.
Negative-side waterproofing often presents itself as the only option in these different scenarios. The success of your negative-side waterproofing will depend on its ability to resist the intensive high-water pressure, or hydrostatic pressure, from the positive side of your structure.
Does Negative-Side Waterproofing Have Limitations?
In short, yes. Negative-side waterproofing will not prevent the water from entering your substrate, but it will prevent water from entering the occupied space. In order to apply an “internal negative-side waterproofing system,” your internal surfaces must be able to accept your waterproofing treatment. You need to prep your surface so that your waterproofing material adheres as you need it to for the best waterproofing protection. It is extremely important that the waterproofing material that is selected can withstand the hydrostatic pressure, but also not de-bond due to the pressures acting on the bond. Your waterproofing material should also be free of chlorides, so you’re not harming your steel reinforcement in any way.
Negative-side waterproofing is not appropriate in the following situations:
- If there will be exposure to corrosive materials in the soil
- If your building is in a region with exposure to freeze-thaw cycles
- If the building will have interior humidity limitations, such as a greenhouse, an indoor pool or skating rink
What Are My Negative-Side Waterproofing Materials Options?
There are various options for negative-side waterproofing materials: two effective types of materials are crystalline surface coatings and flexible cementitious coatings. They work in two very different ways:
Crystalline Coatings are typically a one-component product comprised of a Portland cement-based coating (slurry) that contains silica-based materials. Underwater pressure (negative or positive), the soluble silicate penetrates (due to osmotic pressure) into the substrate, where it reacts with lime and forms insoluble calcium silicate crystals that “plug” the capillary pores and waterproof the concrete, while still allowing water vapor to pass. This type of product is ideal for your projects such as:
- New or existing water storage
- Water treatment concrete structures
- Utility vaults
- Retaining walls
- concrete slabs
- Swimming pools
- Other concrete structures
Flexible Cementitious Coatings are used when your project calls for superior flexibility. These are highly flexible, fiber-reinforced, breathable, cementitious slurries typically comprised of two components: dry and liquid. These membranes are designed for positive and negative waterproofing, for new construction and restoration (used over the cracks in concrete to provide bridging). Fully trained contractors will push the coating into the problematic pathways for it to harden, providing you with a secondary, cement-based barrier. In new construction, it is a suitable material for the following projects:
- Water and wastewater tanks
- Secondary containment structures
- Concrete slabs
- Patios with light-to-medium traffic
What are the Advantages of Negative-Side Waterproofing?
Industry experts will typically cite these four advantages:
- While you need to be fully trained to apply either of these products, the training isn’t complicated, and the product is easy to apply.
- It’s cost-effective.
- You have full visibility into where you’re applying it, and you can easily repair it.
- You have the convenience of knowing it can be applied any time after the substrate material has cured.
How Do I Prep My Substrate for These Materials?
Whether you use crystalline or flexible cementitious coatings, both applications will require unimpeded access to your base substrate material so that there is no contamination that will affect the penetration, or adhesion, of the material. To that end, we recommend the following:
Remove any previous surface coatings, paints, efflorescence, dirt or foreign materials that will obstruct the penetration and proper bonding that must occur to ensure you have a successful waterproofing solution. You may resort to sandblasting, shotblasting, or high-pressure water blasting to ensure your substrate has a better profile, especially if it was originally a smooth-troweled or precast substrate.
What If I Have an Actively Flowing Water Leak?
In situations like this, you can’t bring a Prius to win a NASCAR race. This requires a next-level solution: “hydraulic cement.” Hydraulic cement will plug an active, flowing water leak, and it sets within three to four minutes. If you have an actively leaking crack up to 19 mm or ¾” wide and/or 19 mm or ¾” deep, hydraulic cement is your best solution. However, this is not a simple application. Since it’s a Portland cement-based material, you need to wear a respirator because inhaling Portland cement is hazardous. Additionally, you must not allow this material to have any contact with your skin because it generates heat during when you activate it by mixing it with water, and this can cause severe chemical burns.
To conclude, negative-side waterproofing has an important role to play in protecting your structure because there are countless situations where it will become your only option and the most effective solution.
LEARN MORE: please call one of our experienced inside sales associates at (800) 342-5976
P.S. LEARN MORE–Negative-Side Waterproofing Solutions by W. R. MEADOWS: