Case Study: Drainage Fix and Interlock Patio in the Plateau

This project tackled two problems at once: a deteriorating concrete slab and a drainage failure that had been pushing water toward the foundation for years. The outcome was a modern interlock paver patio with proper grading and drainage infrastructure that fixed both issues for good.

Project: Plateau Paver Patio Location: Montreal, Plateau-Mont-Royal Duration: 6 working days Services: Patio installation, drainage solutions, interlock pavers

The problem

The homeowner's backyard had a concrete slab that dated to the 1980s. After decades of Montreal freeze-thaw cycles, the slab was extensively cracked, with sections that had heaved and settled unevenly. Uneven surfaces created tripping hazards, and gaps between the cracked sections allowed water to pool underneath.

The drainage was worse than it looked from the surface. Water pooled on the patio after every rainfall and had no clear path away from the building. Over the years, this had contributed to basement moisture issues.

What we found during demolition

Removing the old concrete revealed the root cause of the problems: the original slab had been poured directly over clay soil with no proper base whatsoever. No gravel base, no compaction, no drainage infrastructure. The concrete was essentially floating on top of clay that expands when wet and contracts when dry, which is exactly why it cracked and shifted.

This is common in older Montreal properties. Before modern building codes and installation standards, concrete was routinely poured directly on native soil. It might look fine for the first few years, but Montreal's freeze-thaw cycles eventually wreck any slab without a proper base.

The solution

Excavation and base preparation

After removing the old concrete and hauling away the debris, we excavated to a depth that allowed for a proper layered base system. In the Plateau, lot access is often limited, and this property was no exception. Material delivery and debris removal had to be coordinated carefully to avoid disrupting the laneway and neighboring properties.

We installed a geotextile membrane over the exposed clay subsoil. This membrane stops clay particles from working their way up into the gravel base over time, which would choke off drainage and weaken the structure.

On top of the membrane, we built up a base of compacted 0-3/4 inch crushed limestone. The base was installed in 4-inch lifts, with each lift mechanically compacted before the next was added. Total base depth reached 10 inches, providing well above the minimum required for a residential patio.

Grading and drainage

The base was graded with a consistent 2% slope away from the building, directing surface water toward the rear of the yard. This slope is subtle enough that you don't see it, but steep enough to move water reliably.

At the transition between the patio surface and the adjacent yard, we installed a linear channel drain. This channel captures any water that runs across the patio surface before it reaches the garden beds, preventing erosion and ensuring the drainage system works as a complete unit.

Paver installation

We installed Techo-Bloc Blu 60mm pavers in Champlain Grey, laid in a herringbone pattern. The herringbone layout was chosen for its structural performance: discontinuous joint lines distribute loads evenly and resist the lateral shifting that simpler patterns are prone to during frost heave.

The joints between pavers were filled with polymeric sand, which locks the pavers together as a unified surface, prevents weed growth, and resists washout from rain.

Edge restraints

Concrete edge restraints were installed around the full perimeter of the patio and secured with 10-inch spikes driven into the base. Edge restraints prevent the outermost pavers from creeping outward over time, which would create gaps and compromise the structural integrity of the pattern.

The result

The homeowner confirmed the drainage issues were completely gone after the first heavy rainstorm following completion. Water moved off the patio surface as designed, the channel drain captured edge runoff, and no pooling occurred anywhere on or near the new surface.

The finished patio provided a level, stable surface for outdoor furniture and use, replacing what had become an unsafe and deteriorating space. The Champlain Grey color and herringbone pattern complement the character of the Plateau neighborhood while providing a surface that will handle decades of Montreal weather.

Key takeaways for homeowners

The base matters more than the surface. The original concrete failed because it had no base. The pavers will last because the base is engineered for Montreal's soil and climate. When comparing quotes from different landscapers, ask about base depth and preparation. Cutting corners on the base causes exactly the kind of failure this project was built to fix.

Drainage isn't optional. Every patio installation should include a grading plan that moves water away from the building. If the existing grade slopes toward the house (as it did in this case), correcting the grade must be part of the project scope.

Old concrete removal often reveals surprises. Budget for the possibility that the subgrade beneath old concrete will need more work than expected. In this case, the complete lack of an original base meant we needed to excavate deeper and install more gravel than would have been necessary over a previously prepared subgrade.

Narrow lot access is manageable. Plateau and other dense Montreal neighborhoods require careful logistics for material delivery and debris removal. Experienced crews plan for these constraints as part of the project timeline.

View the full project

See the complete project details and additional information on our Plateau Paver Patio project page.

For a similar project on your property, call Montreal Paysagement Pro at 514-900-3867. We provide estimates by phone, photo, or video.