Foundation and waterproofing work happens quickly and largely out of sight — concrete is cut, systems are installed, and everything is covered up before many homeowners think to look. The critical stages to observe are the ones before things get buried: the drainage channel before concrete is poured over it, the excavated wall before the membrane is applied, the sump pit before the pump is installed. These are the moments when problems are visible and correctable.

“For interior drainage jobs, the most important thing a homeowner can do is ask to see the drainage channel before the concrete goes back. Confirm the channel is sloped toward the sump pit, confirm the stone bed is there, and confirm the channel is in contact with the base of the wall — not floating in the middle of the floor. Once the concrete is poured, those things are invisible for the next thirty years.”

— Patrick Osei, licensed structural engineer and foundation consultant with 22 years of experience in residential foundation assessment and waterproofing in the local area

During Interior Drainage Installation

Architects wearing hard hats review blueprints inside a building under construction.

Can I see the drainage channel before concrete is poured?

This is the most important request during an interior drainage installation. After the trench is cut and the drainage channel is placed, but before concrete restoration begins, ask to inspect:

  • Channel slope: The drainage channel must slope toward the sump pit — water doesn’t flow uphill. Confirm the slope is consistent.
  • Channel position: The channel should be positioned against the base of the foundation wall, not in the middle of the floor, to intercept water at its point of entry.
  • Stone bed: A bed of clean crushed stone beneath the drainage channel allows water to percolate into the channel from below.
  • Channel continuity: The channel should run continuously around the perimeter without gaps.

What a good answer looks like: The contractor inviting you to inspect before concrete is poured. Any contractor who objects to this inspection is a red flag.

What is the sump pit configuration?

Ask to see the sump pit before the pump is installed:

  • What is the pit diameter and depth?
  • Is the pit perforated to allow groundwater to enter from below?
  • Is the pit cover included (with an airtight seal to prevent radon gas and humidity from entering)?

What sump pump model is being installed, and what is its rated capacity?

Ask for the specific pump model and its rated flow rate in litres or gallons per hour. Cross-reference this against the drainage area it’s serving — an undersized pump in a high-water-table location won’t keep up during a major rain event.

Is a backup pump being installed?

A sump pump that fails during a heavy rain — the exact conditions under which it’s most needed — can result in thousands of dollars of basement flooding. Ask whether a battery backup pump is being installed alongside the primary pump, and if not, why not.

During Exterior Waterproofing

Team of construction workers using power tools to level freshly poured concrete on a building site.

Can I see the excavated wall before the membrane is applied?

After excavation and before the waterproofing membrane is applied, ask to see the exposed foundation wall. This is the only opportunity to see:

  • The condition of the existing foundation — any cracks, spalling, or surface damage
  • Whether the old exterior membrane has completely failed
  • Whether there are any structural concerns visible from the exterior

Take your own photographs at this stage.

What surface preparation is being done before the membrane?

The foundation wall surface must be prepared before a new waterproofing membrane can be applied effectively — cleaning, repairing cracks, applying a primer coat if required. Ask the contractor to describe the preparation steps and confirm they’re being followed.

What waterproofing membrane is being applied?

Ask for the specific product being applied — brand and type. Common exterior waterproofing systems include:

  • Dimple mat systems (Delta-MS, Platon): A dimpled plastic sheet that creates an air gap between the membrane and the soil, allowing any residual moisture to drain down to the weeping tile rather than penetrating the wall. Effective and durable.
  • Rubberized asphalt coatings (Bakor, W.R. Meadows): Applied hot or cold, creates a seamless waterproof layer. Effective when properly applied at adequate thickness.
  • Spray-applied membrane systems: Applied as a liquid that cures to a flexible membrane. Seamless application.

Ask why the proposed system is appropriate for your foundation type and soil conditions.

Is new weeping tile being installed?

If existing weeping tile is failed, crushed, or absent, it should be replaced as part of an exterior waterproofing job. Ask whether new perforated drain pipe is being installed at the footing level and where it will discharge.

What backfill material is being used?

The excavated area should be backfilled with free-draining material — clean crushed stone (HL3 or equivalent) near the wall transitioning to native or compacted fill further out. Native clay soil compacted directly against the new membrane can damage it and impede drainage. Ask what the backfill specification is.

During Crack Injection

Can I see the injection ports before the work begins?

Crack injection involves drilling ports into the crack at regular intervals and injecting polyurethane or epoxy under pressure. Ask to see the port layout before injection begins — ports should be spaced 20–30 cm (8–12 inches) apart and positioned to ensure complete fill of the crack.

How will you confirm the crack is fully filled?

Ask how the contractor confirms the crack has been completely filled with injection material. For through-cracks, material appearing on the exterior side of the wall confirms complete penetration. For interior-only cracks, pressure confirmation during injection is the primary verification.

End of Job Inspection

Before final payment, walk through these items:

Interior drainage: Confirm the concrete restoration is complete and clean, the pump activates when water is added to the pit, the discharge pipe is properly directed away from the foundation, and all debris has been removed.

Exterior waterproofing: Confirm the backfill is properly graded away from the foundation, any surface restoration (landscaping, driveway) is complete to the agreed standard, and no membrane is exposed above grade.

Crack injection: Confirm all ports have been capped and the exterior crack surface (if visible) shows injection material.

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