What Landscaping Fabric Does Under Your Patio — and Why It Matters

It's important to keep soil from mixing in with the base stone on a patio. For this, we use geotextile, a.k.a. landscaping fabric.

The lack of geotextile between subsoil and base stone reduces the lifespan of a patio. Let’s break it down using a first-principles approach. This means starting with fundamental concepts and building up logically to understand the role of each component in patio construction.

Understanding the Components

The subsoil is the natural soil layer beneath the topsoil. It is compact and in Winnipeg it is very fine-grained. The base stone, for the patios we build, is crushed stone. This is a very coarse, well-draining layer placed over the subsoil to provide a stable foundation for the patio surface. A geotextile is a permeable fabric used in construction to separate soil layers and filter water.

The Role of the Geotextile

In patio construction, we excavate the topsoil and compact the subsoil. We then lay the base stone into that hole and compact that as well. We then install the surface layer, usually concrete pavers.

In that process, we place geotextile between the subsoil and base stone. This serves a critical purpose: separation. It prevents the fine particles of the subsoil from mixing with the coarser base stone.

Why Separation Matters

The base stone is meant to provide stability and drainage. Its coarse structure has natural voids that allow water to pass through, even when it is compacted to be very strong and ridged. The fact that water can flow through the base prevents water from accumulating beneath the patio.

If fine subsoil particles migrate into these voids in the base stone — a process sometimes called "pumping" which is due to water movement or surface loads — they can clog the base stone. This has two major effects:

1. Reduced Drainage: Clogged voids impair water flow, leading to accumulation. In wet conditions, this can soften the foundation, causing it to shift or settle. In colder climates like Winnipeg's, trapped water may freeze and expand (frost heave), pushing the patio surface upward and causing cracks or unevenness.
2. Compromised Stability: Subsoil is typically weaker and less load-bearing than base stone. If it mixes in, the base layer’s ability to evenly distribute loads on the surface diminishes. This can lead to settling, shifting, or sinking of the patio surface over time.

Without the geotextile, these issues develop gradually as environmental factors like rain and mechanical stress drive subsoil upward into the base stone.

Consequences for Lifespan

A patio’s lifespan is tied to how long its surface remains functional and intact. If the base stone loses its drainage and stability:

• Pavers may become loose or uneven.
• Concrete slabs may crack or sink due to uneven support.

These failures necessitate repairs or replacement sooner than if the foundation remained intact. Geotextile between the subsoil and the base reduces issues like settling, cracking, or heaving, which will shorten the patio’s functional lifespan.