Basement Sealing

Contacts

• APS Waterproofing
  • 678-315-7761
  • VFV7+G5 Smyrna, Georgia
  • 11 miles
  • Michael, texted 2026-08-25 08:47
• All-American Waterproofing
  • 404-301-3431
  • MFMQ+M7 Atlanta, Georgia
  • 12 miles
  • bigger place with a call system
  • left a message 08:50
  • scheduled meeting 2026-08-27 10a-12p
• Lifetime Basement Waterproofing
  • 770-607-3838
  • QJQ7+5W Atlanta, Georgia
  • 15 miles
  • Tina
  • txt: 678-580-9694

External Basement Waterproofing: Process & Checklist

External basement waterproofing is the gold standard for below-grade water management. By excavating around the foundation and treating the exterior face of the walls, this method stops water before it touches the concrete structure and relieves hydrostatic pressure at the perimeter.

Part 1: Excavation & Waterproofing Process

Step 1: Site Preparation & Trench Excavation

• Excavation Depth: Heavy machinery or hand tools excavate a trench around the foundation perimeter down to the top (and outer edge) of the concrete footing.
• Safety & Bench/Shoring: Depending on soil stability and depth, trenches must be sloped back, benched, or shored with trench shields to prevent soil collapse during installation.
• Utility Clearance: All underground lines (gas, power, water, fiber) are located, marked, and carefully hand-dug around near the foundation.

Step 2: Wall Cleaning & Substrate Surface Prep

• High-Pressure Cleaning: The exposed foundation wall is pressure washed to remove dirt, loose mortar, clay residue, and old degraded coatings.
• Structural Crack & Joint Repair: Cracks, honeycombing in poured concrete, or degraded mortar joints in masonry blocks are excavated and filled with non-shrink hydraulic cement or structural epoxy mortar.
• Parging (Masonry/Rough Concrete): A fresh parge coat (smooth cementitious mortar layer) is applied to block or rough walls to ensure a continuous, flat substrate.
• Footing Cove (Fillet): A 45-degree concrete fillet or cove is constructed at the right-angle joint where the wall meets the top of the footing. This prevents water from pooling in the sharp corner.

Step 3: Primary Waterproofing Membrane Layer

Note: Asphalt "damp-proofing" coating (black foundation paint) is not waterproofing. Waterproofing materials must span hairline cracks and withstand continuous hydrostatic pressure.

• Membrane Material: Thick rubberized asphalt, elastomeric liquid membrane, or cold-applied self-adhering modified bitumen sheets are applied to the primed wall.
• Coverage: The barrier spans from below the top edge of the footing up to finished ground level grade line.
• Reinforcement: Critical stress points, structural cracks, and wall-to-footing transitions are reinforced with embedded synthetic fabric or fiberglass mesh.

Step 4: Protection & Vertical Drainage Board (Dimple Mat)

• High-Density Polyethylene (HDPE) Mat: A heavy dimpled drainage board is mechanically fastened over the rubber waterproofing membrane (dimples facing toward the wall).
• Dual Protection:
  1. Mechanical Protection: Shields the delicate liquid/sheet membrane from sharp rocks during backfilling.
  2. Drainage Channel: Creates an uninterrupted vertical air gap so any surface water immediately drops straight down to the footing pipe.
• Termination Strip: Heavy plastic or metal flashing is sealed to the top edge above ground level to prevent dirt and surface runoff from slipping behind the dimple mat.

Step 5: Footing Drain Tile & Filtration Matrix

• Drain Pipe Selection: Smooth-bore perforated rigid PVC (ASTM D3034 or Schedule 40) is preferred over flexible corrugated black pipe because it resists crushing and maintains pitch.
• Slope & Layout: The pipe sits along the outer edge of the footing (sloped at a minimum 1/8 inch per foot) toward a gravity outlet or internal/external sump basin.
• Washed Aggregate: 12 to 18 inches of clean, washed aggregate (e.g., #57 crushed stone) completely encapsulates the perforated pipe.
• Geotextile Filter Fabric: Heavy needle-punched non-woven filter fabric wraps the gravel envelope to prevent silt and soil fines from clogging the drain line.

Step 6: Backfilling, Compaction & Grading

• Layered Backfilling: Backfill soil is replaced in 8- to 12-inch lifts and compacted to minimize future settling.
• Positive Pitch: The final topsoil is sloped away from the foundation wall at a minimum grade of 6 inches over the first 10 feet.
• Surface Water Management: Roof downspouts and yard runoff are piped completely outside the excavation footprint to avoid re-saturating the backfilled zone.

Part 2: Essential Questions to Ask Your Waterproofing Contractor