Poured Concrete Foundation Construction and Waterproofing

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To understand basement waterproofing methods best suited to poured concrete foundations it is crucial that you understand how this type of foundation is built, as well as its general characteristics.

 

How a Poured Concrete Foundation is Constructed - Step by Step

The images below show the sequence of steps followed in building a poured concrete foundation; including foundation waterproofing, damp proofing and weeping tile installation.

 

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Step 1 - Excavation of the soil

The first step in the construction of any home is excavation; this is because the foundation is, and must be, built first. The remainder of the home will be entirely supported by the foundation.


 

The first step is the excavation of the lot to the desired basement depth

Terrain is levelled to get desired foundation depth

Step 2 - Forming of the footings

In order to erect the foundation on a stable surface, a concrete stratum, called a footing (or footer), needs to be poured. A footing is usually a 16" wide (twice the foundation width) and 8" thick slab of poured concrete positioned to support future load bearing foundation walls as well as support posts for inside load bearing walls. In the image below, you can see the wooden forms for the footings that will be poured. 


 

Forms to pour the footing are placed within the excavated area
 Forming in place for the footing to be poured

Step 3 - Pouring of the footings

ln this next image we can see the poured footings as well as square shaped forms for foots beneath the future support posts that will be erected in the basement. These support posts will support a steel I-beam which will bear the weight of the middle of the house.


Footings are now in place and ready to support the foundation walls
 The footings support all load bearing walls of the home

 

If you look closely at the picture below and you will notice that the footing is quite thick; in fact, there are actually two footings, one poured on top of the other. This is not standard construction, two footings were poured because the initial pour was too low, as a result, the foundation would have been too deep for the planned foundation height. An alternative to the pouring of a second footing is the addition of concrete blocks on the top of the poured foundation until the desired height of the foundation is achieved.

Rebar is installed on the footings to strengthen the structure

Step 4 - Installation of the forms for the foundation walls

With the footings in place, the forming crews install the forms into which concrete will be pumped. In this particular application, tie-rods are being used; these rods will keep the plywood forms at exactly 8" apart, which is the standard foundation thickness for foundations across the GTA today.

Forms are erected in which the concrete will be poured and cured

 

Step 5 - Disassembly of the forms

When the concrete has cured sufficiently the forms are removed. After removal we can see the vertical seams between the sheets of plywood that were removed. We can also see circular concrete patches used fo fill the holes left behind after the tie-rods are removed. Similar patches are normally visible on the interior of the basement as well.

 

Once the concrete has cured, the tie-rod holes are covered over and weeping tile is installed

 

Variations in forming

The following image is typical of how a foundation steps down in order to accommodate a walkout basement.

Once the concrete has cured the forms are removed

 

 

Step 6 - Waterproofing of the foundation

To waterproof the foundation contractors spray a thin layer of tar onto the exterior foundation walls

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An air gap membrane is installed over the tar to provide damp-proofing of the walls. The weeping tile will drain away water that accumulates at the base of the foundation.

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Once the walls are waterproofed and the weeping tile is tied into a drainage point the soil is backfilled against the foundation walls

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Footings are installed beneath the basement floor to support the support posts that support the I-beams that bear the load of the interior of the home

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Once support posts are in place, the basement floor is covered with gravel and then the concrete floor is poured