Piedmont Waterproofing Contractors

Interior vs. Exterior Waterproofing

Exterior Waterproofing

Answers to Common Questions about Waterproofing

November 7th, 2019

Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. When it comes to waterproofing structures, there are several different approaches that can be taken. The idea of waterproofing can seem very daunting. One of the biggest questions that comes up is, “should I go with interior or exterior waterproofing?” We are here to give you the benefits of each and provide a little more insight as to which choice may be the best route for you.

Interior Waterproofing - Negative Side Water Management

Interior waterproofing, also known as negative side waterproofing, is the process of applying a protective layer to the dry or inside face of the subsurface. The primary purpose for negative side waterproofing is for water holding. In other words, negative side waterproofing will prevent water from entering a certain space, however it will not prevent water from entering the substrate. Since water will still be in contact with the substrate, this can lead to mold growth, deterioration of foundation material, and other problems associated with moisture.

There are some distinct advantages to interior waterproofing. The major advantage is that it can be much less intrusive than exterior waterproofing. The negative side can be much more accessible as well, making it easier to identify leaks. Overall, interior waterproofing is usually less costly than its exterior counterpart. It entirely depends on which route you go when it comes to waterproofing. Here are a couple of examples of different solutions used:

Interior Waterproofing Injection

Injection Waterproofing Method

    • Retail interior wall coatings: These are the least expensive and least time consuming solution for the negative side waterproofing. You can usually find several brands and types of waterproofing materials at your local hardware store.  These include waterproofing paints and wall coatings that are applied directly onto the interior walls.  Unfortunately, these coatings are temporary at best, and not likely to last very long.
    • Interior drain / pump system: These systems are technically not waterproofing and are considered “water management systems”.  The systems can very effective if they are installed correctly.  One advantage to choosing these systems is it is much easier to install, especially if there is no room on the exterior to excavate safely or if it requires a large amount of exterior hardscape/landscaping.
    • Injection method: The injection method is the process of drilling injection holes into a space and injecting a material inside so that a continuous water barrier is formed.  There are many types of injection materials that can be used for this method, and it can be done from the interior or exterior.  This method is minimally invasive, however it is not a very common practice and is relatively expensive.  Usually only used for “rising damp” issues as seen in the photo.

Sometimes with interior waterproofing, exterior improvements should be made at the same time.  An example of this would be extending a downspout outfall 10′ or more downhill away from the foundation.  Thus preventing moisture from building up close to your foundation.  Another thing to note is that sometimes these interior methods will carry warranties with them, giving you peace of mind to your new waterproofed location.

Exterior Waterproofing - Positive Side Water Management

Exterior waterproofing, also known as positive side waterproofing, is the process of applying a protective layer to the wet or exterior side of a foundation or slab. This can be done grade, below grade, or both. Unlike negative side waterproofing, exterior waterproofing when properly applied will protect the substrate from any moisture. Since the substrate is protected, the structural components are better protected and will typically last longer. The procedure is meant to stop water before it migrates into CMU cores or through cracks in the foundation.

When positive side waterproofing is used, it most often results in much better drainage via a new drain tile/downspout system. The main disadvantage with choosing exterior waterproofing is that it requires enough room to properly create a safe excavation in order to access all parts of the suspect foundation. Therefore, when it comes to new construction, this is usually the method used to waterproof a structure. In addition, it also requires a spot near the foundation to properly outlet the downspouts and the new drain tile system downhill away from the foundation. The system is sometimes inaccessible after installation as well and usually requires the moving of hardscape or landscaping to get to the installed system.

Although exterior systems are typically costlier than the interior, the longevity is much better in the former. Since the substrate is protected, moisture does not have a chance to build up and begin deteriorating the foundation. The risk of ground contaminants and chemicals is always present with moisture so by using the positive side waterproofing, you are preventing these from reach the foundation. There are several different approaches to exterior waterproofing such as:

      • Vapor Barrier: These barriers are used to prevent moisture from reaching a surface in order to prevent water damage.  There are many different types of materials that can be used, and in turn have different levels of effectiveness.  Based on the effectiveness of the material, there are three classes by which the materials are grouped.  These are typically only done underneath floor slabs.
      • Waterproofing Membrane: There are two types of waterproofing membranes: sheet-based and liquid applied. Both act in the same manner. The layer of membrane is strewn across a surface, which is continuous so that no water can pass through it. Waterproofing membranes must be strong and durable to resist the changes in weather and exposure to contaminants in the moisture. Membranes are usually quick to install onto flat surfaces although the cost can be a bit more than vapor barriers.
Positive Waterproofing Blueskin

Blueskin® Composite Membrane

There are quite a number of different vapor barriers and waterproofing membranes that can be used.  They have varying degrees of effectiveness, cost, and ease of installation.  There are many factors that are considered when determining which approach to use.  


There are many advantages and disadvantages to both exterior and interior waterproofing. Interior waterproofing is usually more economically friendly, much easier to access, and easier to identify leaks. The cheaper options for interior waterproofing are usually only temporary and should not be used as a permanent solution. Water management can also be used in place of waterproofing when working in the interior. It is a great solution for keep water pumped out of your basement.

Exterior waterproofing is used for many new builds and is usually put in place as a lasting solution. Cost varies for exterior, but it is usually a bit more expensive than interior. It is much more difficult to retrofit exterior solutions as enough room is required in order to excavate around all places that need to be worked on. Exterior waterproofing provides longevity to your structure by preventing moisture to reach the substrate.

In conclusion, there is no one-size fits all approach to waterproofing. Every project requires a different level of intervention and waterproofing. Hopefully this information will give you a better idea of the different options out there for waterproofing. If you have any questions or need clarification about any of this, feel free to send us an email or give us a call. We are always here to help.

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