The Block Foundation

May 16, 2013

The biggest challenge with cinder block, construction-block, cement block or concrete block foundations is that the foundation wall is hollow.

The blocks each have two empty chambers which can fill with water and travel throughout the hollow foundation wall. The hollow nature of the foundation makes it more challenging to repair than a solid poured concrete foundation because you never know where the wall is leaking from, only where the water comes out of the wall inside. The actual source of the leak can be many feet away from where the water is seen on the inside.

There Are Two Methods of Correction

External excavation and waterproofing and the internal sub-floor drainage system or French-drain.

External waterproofing involves excavating to expose the entire foundation wall from one end to the other and from top to bottom. Waterproof membranes are installed to prevent water from entering the foundation wall and the basement. Weeping-tiles can also be replaced at this time.

The internal sub floor drainage system involves creating a trench through the basement floor, installing subfloor drainage system under the floor, drilling drainage holes in the bottom blocks under the floor to ensure drainage of water from the wall and provide active drainage by connecting the system to a sump pump. Often a waterproof membrane is installed to the foundation wall which connects to the drainage system under the floor. New concrete is then poured to repair the floor.

The external approach can be successful but it is necessary to treat the full length of the wall since the wall is hollow. This approach has limitations due to additions, sunrooms, garages, decks, patios landscaping, porch’s neighbours, driveways, fences, price etc and since all basements were once already made waterproof from the outside this approach can only be considered a temporary repair.

The internal subfloor drainage system creates a path of least resistance outside of the building envelope under the floor which can be serviced and inspected providing a permanent solution.

Renovation or construction would occur as usual with no special considerations.

The internal sub-floor drainage system costs about half as much as the outside solution.

THE CRACK DOCTOR routinely performs both repairs, with full confidence throughout Ontario. Many repairs carry our famous lifetime transferable warranty.

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