Bricks That Adapt to Movement in Winnipeg's Clay Soils

by Dwayne Regehr

Organic materials in the ground, like soil and clay absorb water and therefore expand. Given some time without rain, these same materials will dry out and shrink. This movement of the ground is a fact of life, especially with our Winnipeg clay. So, before we build anything here, we have to take it into account.

There are two strategies for dealing with inevitable movement of the ground.

1. Build a structure so massive and monolithic that it will remain rigid on top of the moving ground without cracking and shifting. Most concrete driveways in Manitoba are an attempt at this strategy. A 6" to 8" thick concrete slab, laced with reinforcing steel bars, will do its best to resist the movement of the ground beneath it. But, we have all seen how well that works! It doesn't take long and there are cracks.

2. The second strategy is to accept that soil movement will happen and build a structure with the flexibility to move along with it.

The patios and retaining walls that we build employ the second strategy. Concrete pavers and modular retaining walls are flexible systems that can move along with the seasonal changes in the soil moisture content.

How do we do this?

Part of the magic is to control the movement of water through the patio and in the ground below.

Laying the foundation

First, we remove as much organic material as possible – organic material is what absorbs water and therefore changes in volume. The area under your future patio will be excavated to a depth of 8" to 10" (or more, if necessary). The organic material will be replaced with an inorganic foundation of crushed stone. 3/4" down crushed limestone has excellent drainage properties, allowing moisture to drain away from the surface of the patio where it can do the most damage. To increase load-bearing capacity and prevent settling, the crushed stone is pressed down with a vibrating plate compactor.

Two other things improve the stone base.

1. We install a geo-textile membrane, sometimes called landscaping fabric, as a barrier between the stone base and the clay sub-soil. The geo-textile is a water-permeable fabric that allows water to drain out of the base stone while preventing the clay sub-soil from mixing with the foundation.

2. We ensure that the stone base extends beyond the finished square footage of the patio, driveway or retaining wall.

Brick system

With the construction of a proper foundation we have done what we can to minimize and control the movement of the ground. But unfortunately, we cannot eliminate movement, so for the surface itself, we need to use materials that will accommodate movement. This is where concrete pavers and modular retaining walls come in. Rather than a single piece of concrete, hundreds of bricks allow for minute movement between units.

It gets better. If concrete pavers functioned completely independently of each other this would already be superior to poured concrete, but the addition of joint sand allows the pavers to act as one large system. When polymeric sand is swept into the spaces between bricks, it creates an interlock between adjacent bricks. Pressure applied to a single brick is transferred to all adjacent pavers.

As an added bonus, this system makes repairs very easy.

It's a great system!

We'd love to make this happen for your landscaping project. Send us an email at dwayne@earthworkslandscaping.ca to chat about it.