Concrete Block Waterproofing - Essential Knowledge

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The unfortunate reality is, when it comes to concrete block foundations, that it’s really just a matter of time before concrete block waterproofing is required. The need to waterproof concrete block foundations is attributable to the construction and inherent characteristics of concrete blocks. A concrete block foundation is prone to producing basement leaks and/or leaks in any underground space that has concrete block (also referred to as cinder block) walls.

Why Concrete Block Foundation Walls Leak

The problem with concrete block walls is that the mortar joints between the blocks typically develop hairline cracks over time. This hairline cracking is usually the result of thermal cycling of the both the concrete blocks and the mortar binding them together. This doesn’t mean that cracking occurs only within mortar joints; sometimes other cracks are present in concrete block foundation walls. The concrete blocks themselves typically crack when there is settlement of the footing supporting the foundation walls, and when there is excessive soil pressure against the foundation.

Unless there is significant settlement of the footing, minor cracking in the mortar joints is not really a problem from a structural point of view; unless the crack is horizontal. However, hydrostatic pressure (water pressure against the exterior wall) forces water into these hairline cracks; this is where basement leak problems begin.

Concrete blocks are not solid concrete; in fact, they are largely hollow.

A hairline crack in a mortar joint, or a crack within a concrete block, allows water to enter the hollow areas of the concrete block. When this water encounters these hollow areas, the water drains downwards and typically pools in the lower courses of the concrete block wall (the rows of concrete blocks closest to the floor). The water is now trapped in the concrete blocks; in some cases substantial amounts of water can be trapped within walls – check out the image below.

This trapped water, typically saturates the concrete blocks causing them to weep or leak onto the basement floor. Additionally, if the cracks in the mortar joints are sufficiently large and there is a sufficient hydrostatic pressure, water will leak into a basement from the mortar joints between the concrete blocks.

Concrete block foundation cracks and hydrostatic pressure, which is present on the exterior of the foundation, are responsible for leaking concrete block walls. This leaking and/ or seepage into basements creates significant demand for concrete block waterproofing; particularly for homes built between 1950 and the late 1970s in areas such as Burlington, Oakville, Mississauga, Etobicoke, Scarborough, Newmarket, Brampton and Richmond Hill.

Concrete Block Waterproofing Methods

Waterproofing concrete block foundations can only accomplished using either of the following two methods:

1. Internal de-watering of the concrete block wall, (often referred to as an interior weeping tile system); and
2. Waterproofing the exterior concrete block walls by excavating the foundation walls and applying an effective coating to prevent water from coming into contact with the concrete blocks and mortar joints.

Concrete block waterproofing, regardless of the waterproofing method chosen, is intrusive and costs thousands of dollars. Fortunately, concrete block waterproofing, when done professionally with the appropriate products, will provide you with a dry basement for many years.

Links to details about concrete block waterproofing methods

Interior basement drainage system / interior weeping tile system

Exterior concrete block waterproofing

Concrete block foundation leaks can occur at any time, regardless of the season. To schedule an appointment to find out which concrete block waterproofing method is best for you, Contact us.

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