S. Altan Atasoy, Civil Engineer
October 5, 2026

North Potomac MD Basement Seepage: Exterior Waterproofing and Grading Tile

A North Potomac homeowner called about water seeping into the basement and a French drain they believed was clogged. The question was not just whether the old line could be cleared: water was also reaching the foundation wall. Our completed project addressed the buried wall, reshaped the grade, collected approaching surface water in a near-grade grading tile, and carried roof and sump discharge away through separate solid lines.

What was causing concern at this North Potomac basement?

The homeowner reported two symptoms: basement seepage and a drain that no longer seemed to work. A clogged drain was the homeowner’s description, not a verified diagnosis of the old pipe. A drain can move only the water that reaches it and has a functioning outlet; it does not seal cracks or joints in a foundation wall. That is why this job combined wall waterproofing with an exterior water route rather than relying on one repair for both problems.

Hand-excavated trench beside the North Potomac foundation wall — Hand excavation opened the limited work area beside the foundation.

How did the crew waterproof the exterior wall?

The crew hand-excavated the affected section to the wall-to-footing junction. After exposing the wall, they used a grinder and steel wire brushes to remove soil, loose material and deteriorated surface areas. Open areas and the cold joint at the base were repaired with polymer-modified mortar; the joint was shaped into a cove so the new waterproofing could continue across the transition.

A continuous polymer-modified cementitious coating formed the first waterproofing layer. This gray coat is visible in the work photos. Once prepared, the wall received compatible primer and a self-adhered sheet membrane with sealed overlaps as the second layer. XPS board went outside the membrane to protect it when soil was returned. The excavated area was backfilled and compacted in lifts so the finished grade would not readily settle into a low spot beside the house.

Gray cementitious first waterproofing layer on a North Potomac foundation — The gray, polymer-modified cementitious first layer before the sheet membrane.

Black self-adhered sheet membrane on the foundation wall — The second waterproofing layer: self-adhered sheet membrane.

XPS protection board installed outside the waterproofing membrane — XPS board protects the membrane during backfill; it is not a substitute for either waterproofing layer.

How was water redirected before it reached the wall?

The completed scope included grading drain tile, or a near-grade exterior French drain, approximately a foot below finished grade. The crew built up and compacted the soil at the wall, tapering it away from the foundation. A membrane-covered, pitched trench with washed stone and geotextile-wrapped perforated pipe then collected surface water approaching the house and carried it along the run.

Roof water followed a different route. One downspout was buried into a solid pipe rather than feeding directly into the perforated collection bed. Additional solid discharge piping carried water farther toward a pop-up emitter. The job also included a buried sump-pump discharge line; the record does not describe a new interior French drain or a new pump installation. Keeping collection and discharge functions distinct is central to this project’s design.

What work was done inside, and what does the finished record show?

Inside the basement, the crew installed a wall vapor barrier with a termination bar up to the exterior grade line. It manages moisture at the interior wall surface; it does not replace the exterior wall repairs or redirect rainwater outside.

Interior basement wall barrier and upper termination in North Potomac — An interior wall barrier was one part of the completed work.

Four work visits were recorded from September 14 through September 17, 2026, and the job was marked closed on September 18. A later project photo shows the surface soil restored beside the house. The record does not include a measured post-storm test, so we describe the completed installation without claiming a documented rain-event result.

Restored exterior grade beside the North Potomac home after waterproofing — The soil surface beside the treated wall after the exterior work.

North Potomac basement seepage questions

Why can a basement leak even when there is a French drain?

A drain’s elevation, condition, slope and outlet determine which water it can intercept. It does not seal a leaking foundation joint. Here, the homeowner reported both seepage and a possible drain problem, so the project addressed the wall and the exterior water routes together.

Is grading tile the same as an exterior French drain?

In this project, yes. The line was specified near finished grade in a pitched stone bed with a geotextile-wrapped perforated pipe. It collected approaching surface water. Its position in the scope and photos identifies it as grading tile.

Should a downspout connect to the perforated grading tile?

Roof runoff is carried away in solid pipe; a perforated line collects water from the surrounding stone. This job included both a buried downspout and grading tile, with separate functions.

Does an interior wall barrier replace exterior waterproofing?

No. The interior barrier helps manage moisture at the basement wall, while the exterior layers protect the buried foundation. Regrading and drainage handle surface water before it accumulates at that wall.

Basement seepage or drainage trouble in North Potomac? Request an inspection so the entry point and outlet can be traced before choosing a repair. Learn more about our exterior waterproofing service.