A leaking concrete block / cinder block foundation is an unfortunate reality for many homeowners living in homes built between 1920 and 1980. On this page we explain why block foundation walls leak and how these types of foundations are waterproofed.

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How you can confirm your block foundation leaks

You can easily tell if a concrete block foundation leaks just by observing staining on the walls of your basement.

A concrete block wall with evidence that water is trapped within the blocks

Saturated block wall from water trapped
in the blocks

The dampness of the concrete block causes the paint to flake off

Moisture wicking through blocks causes
the paint to peel

There is no denying it, if your foundation walls appear in any way similar to the images above, you have visual confirmation that your concrete block / cinder block walls have water trapped inside the blocks, or moisture wicking through them. If your walls look like this it is highly likely that you have at least occasional basement leaks, moisture wicking through the blocks into the air in your basement causing a damp basement, and/or water entering your home beneath the basement floor slab, and unfortunately, the ideal conditions for the premature deterioration of your foundation walls. There is only one way to solve this problem: waterproof your foundation.

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The illustration below depicts the typical flow of water within concrete block basement walls (double click the image to enlarge it).

How water leaks through a concrete block foundation

Why concrete block / cinder block foundations leak

Block foundation walls have an inherent weakness in that there are mortar joints on all sides of the blocks (the same as any brick wall). There is a general tendency for mortar joints to develop some hairline cracks over time, typically due to the swelling and shrinking (eg. expansion and contraction of clay soils) of the soil in response to precipitation putting hydrostatic pressure on the mortar joints.

Note: A drop in the footing supporting the very base of the foundation also results in mortar joint and block cracking. Below grade hairline cracks in the mortar joints, and cracks in the blocks themselves, are constantly subjected to hydrostatic pressure from the water table surrounding the foundation, thus facilitating the entry of water into what are essentially hollow blocks.

Here are some images of the concrete blocks / cinder blocks that are used in the construction of a foundation wall (this foundation wall type was in widespread use in residential construction between 1920 and 1980).

Older style of concrete block used after the turn of the 20th century Current style of concrete blocks used in foundation construction

Do you find that your basement is too damp? Click on this link for information on damp proofing.



Can you inject leaking concrete block walls?

Homeowners are increasingly aware that pressurized injection (epoxy and polyurethane) is a very economical way to waterproof a leaking basement; consequently, we receive numerous requests for the injection of concrete block / cinder block walls; unfortunately,pressurized injection is not a viable way to waterproof concrete block foundations because the blocks are hollow making it impossible to ensure that the injected resins will remain contained in the area(s) where water is able to penetrate the foundation.

Click on this hyperlink for a summary of available methods for waterproofing a concrete block / cinderblock foundation.

Applying sealants on leaking concrete block walls

Some seemingly knowledgeable people, and companies, would have you believe that the application of a waterproof sealant or tar based product on the inside surface of a concrete block or cinder block wall will fix your leaky basement. While sealing a concrete block foundation wall from inside may temporarily resolve a basement leak, this form of basement waterproofing will, in fact, trap water within the block foundation wall, effectively preventing any evaporation of the moisture trapped within the blocks. As concrete is a porous material, the resultant pooling (entrapment) of water within the cinderblock wall will accelerate the deterioration of the blocks possibly to the point of failure, leading to far greater repair costs with the passage of time and potentially the structural failure of sections of your foundation walls. Surface sealants must be applied on the exterior wall surface, or the side of the wall where there is positive water pressure, in order for your block foundation to be properly waterproofed.

Professional concrete block basement waterproofing methods

Logically, foundation damage and water penetration of the block would be averted by preventing water from entering the concrete blocks in the first place; this is accomplished by exterior excavation and waterproofing or waterproofing external walls. Alternatively, entrapped water in a concrete block wall can be purged by installing an interior weeping tile / perimeter drainage system; both of these basement waterproofing methods will greatly decrease the rate of deterioration of your foundation. Over the years we have encountered numerous situations where foundation walls need to be rebuilt or reinforced to avoid foundation failure (often the result of years of neglect of a known problem); the cost to rebuild a wall or to reinforce it is significant; you want to avoid such a situation if at all possible and block foundation waterproofing is the place to start.

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Selecting the most appropriate repair method for leaking block foundation walls

Fortunately, it is possible to fix concrete block / cinder block wall leaks permanently. To determine which waterproofing method is the most appropriate to your circumstances, either external waterproofing or installing an interior weeping tile system, a number of factors should be taken into account:

  • Whether the basement is finished or unfinished;
  • Whether there is visible mold inside the home;
  • The moisture levels detected behind finished basement walls (indicates if mould is likely present);
  • The condition of the concrete blocks (level of deterioration visible externally and internally, if possible);
  • The accessibility of the areas that need to be waterproofed;
  • Whether or not the water in your basement is a result of a high water table;
  • The landscaping surrounding the home (concrete walkways, decks, fence locations, etc.,);
  • Your willingness to destroy the landscaping around your home, or to fully remove finished basement walls;
  • Your level of concern with respect to the existence of mould behind finished basement walls;
  • Your basement waterproofing budget;
  • Whether you are pragmatic or a purist;
  • Whether or not structural reinforcement of the wall is required;
  • The need for the installation of a window well drain;
  • The desired warranty duration;
  • The condition of the existing weeping tile and the efficiency of the existing city storm water drainage infrastructure;
  • The extent to which basement waterproofing is required; and
  • The waterproofing contractor you choose.

As mentioned above, when dealing with a concrete block foundation there are only 2 professional repair methods for concrete block / cinder block foundation waterproofing. Click on the 2 links below for more detailed information on these waterproofing approaches.

Ready To Look After Your Wet Basement Problem?

Selecting the most suitable basement waterproofing method should always be done in consultation with a true waterproofing professional / waterproofing contractor because expertise is essential. It is a fact that many general contractors and landscapers will try to increase their sales by waterproofing foundation walls. While their waterproofing work might last a few years, if the basement waterproofing is not done properly, the contractor will have to do the entire job all over again. If you do not have the work done by a reputable and established waterproofing contractor with an excellent rating from the Better Business Bureau, how likely is it that your contractor will acknowledge that they are responsible and do the work again at no charge to you? Additionally, waterproofing work requires skill and experience; the importance of the many minor details involved in basement waterproofing cannot be overstated. In reality, the average homeowner is unable to differentiate between an excellent waterproofing job and a lousy job; consequently, the cost of hiring the wrong waterproofing company can be quite significant.     

Want to learn more? Read our blog post entitled: Concrete Block Waterproofing - Essential Knowledge

Hyperlink to a contact page for basement waterproofing