What subgrade waterproofing has to resist
Walls and slabs below grade sit against soil that can stay wet for long periods. When groundwater or trapped surface water builds up against the structure, it pushes on the wall as hydrostatic pressure. A system that only resists dampness will not hold back water under pressure.
That is the practical difference between dampproofing and waterproofing. Dampproofing slows moisture moving through concrete or masonry in soil that drains well. Waterproofing is meant to keep out liquid water under pressure, and it depends on continuity at every seam, corner, and penetration.
Most systems combine a membrane with drainage. A drainage layer against the membrane relieves pressure and carries water down to a footing drain, which must have somewhere to discharge. Protection board or a drainage composite guards the membrane during backfill.
Common failure points below grade
Membranes rarely fail in the middle of a wall. Leaks tend to start at terminations, inside and outside corners, cold joints between concrete placements, form tie holes, and pipe or conduit penetrations. Waterstops at construction joints, where specified, must be continuous and properly positioned to work.
Some walls are waterproofed from the outside after the concrete is placed. Others, built tight to a property line or shoring, use blindside membranes installed before the concrete. Each approach has its own sequencing risks, and damage during reinforcing, concrete placement, or backfill can go unnoticed until water appears.
Drainage problems can overwhelm a sound membrane. A footing drain that is crushed, clogged, disconnected, or set at the wrong elevation leaves water standing against the wall. Surface grading and downspout discharge near the foundation add to the load.
Investigating a buried system
The difficulty with subgrade waterproofing is that the evidence is buried. Investigations usually begin with the plans, specifications, product submittals, and any construction photographs. Interior conditions are then mapped: wet areas, efflorescence, staining, and the location of joints and penetrations.
Moisture readings, controlled water testing at the surface, and camera inspection of drain lines can show where water travels without full excavation. When the evidence points to a specific location, a test pit may be the only way to see the membrane, its laps, and its protection. Each opening is documented before it is closed.
We take field samples to store at our office in case they are needed at trial. If a membrane or accessory appears to have a manufacturing defect, we are aligned with several laboratories that test and analyze product failure.
Plan review and repair planning
Gregg de Haan specializes in plan reviews as they relate to waterproofing above and below grade. Comparing the details as designed with the work as built often clarifies whether a leak traces to design, installation, material, or maintenance.
Our reports pair photo documentation with conceptual repair scopes and cost estimates. Below grade, repair options range from injection and interior systems to excavation and replacement, and each carries different cost and disruption. Setting those options out clearly helps the parties evaluate them on the same facts.
Common warning signs
- 01Damp or darkened areas on below-grade walls or slabs after rain
- 02White mineral deposits (efflorescence) at joints, cracks, or tie holes
- 03Standing water, wet carpet, or lifting floor finishes in lower rooms
- 04Rust staining or mineral buildup at pipe and conduit penetrations
- 05Musty odors or mold growth in basements and below-grade rooms
- 06Water entering at the joint between wall and slab