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Industrial Waterproofing and Fluid-Applied Membrane Systems
Article 16 of 24
Below-Grade Walls, Foundations, Slabs, Pits, and Trenches
Below-grade waterproofing must remain continuous around an irregular structure while resisting groundwater, soil moisture, hydrostatic pressure, construction damage, settlement, and movement. Once the membrane is covered by backfill, concrete, insulation, drainage media, or equipment, locating and repairing a defect can become extremely difficult and expensive. Successful work therefore depends on system planning, correct detailing, controlled installation, inspection, protection, and documentation before the membrane is concealed.
Below-Grade Waterproofing Is a Complete Assembly
The fluid-applied membrane is only one part of the water-management system. Depending on the project, the complete assembly may include:
- Prepared concrete, masonry, or other approved substrate
- Crack, joint, penetration, corner, and transition treatments
- Compatible primer or substrate conditioner
- Fluid-applied waterproofing membrane at the specified dry-film thickness
- Reinforcement at designated details
- Protection board, insulation, or approved protection course
- Drainage composite and filter fabric
- Foundation drain, collection system, sump, or other discharge provision
- Compatible waterstops and joint-sealing materials
Failure of any one component can place demands on the membrane that it was not designed to carry. The contractor should review the entire assembly rather than treating the membrane as an isolated coating.
Waterproofing Is Not the Same as Dampproofing
Dampproofing is generally intended to limit moisture migration where hydrostatic pressure is not present. It should not automatically be substituted for a waterproofing system expected to resist liquid water, groundwater pressure, significant cracking, or leakage into occupied or moisture-sensitive spaces.
Where groundwater, perched water, hydrostatic pressure, critical occupancy, sensitive equipment, or an unacceptable leakage risk exists, the project design should identify a waterproofing assembly suitable for those conditions. The coating contractor should not decide independently that a lower-performance dampproofing product is adequate.
Understand the Water Exposure
Before mobilization, the contractor should understand the water conditions used in the design. Below-grade water may come from:
- Naturally occurring groundwater
- A seasonally rising water table
- Rainwater retained in poorly draining soil
- Irrigation, roof drainage, or surface runoff directed toward the structure
- Leaking utilities, process piping, tanks, or fire-protection systems
- Water collected in pits, trenches, sumps, or depressions
- Condensation or interior moisture migrating toward a cooler assembly
Even when the normal water table is below the structure, temporary water can collect against walls and slabs after heavy rain or during construction. Waterproofing and drainage must be evaluated for credible field conditions, not only ideal long-term conditions.
Hydrostatic Pressure Changes the Risk
Hydrostatic pressure develops when water stands against or beneath a structure. The pressure increases with water depth and can force water through small discontinuities, cracks, joints, penetrations, and poorly bonded areas.
Drainage may reduce the water load, but drainage should not be treated as a substitute for waterproofing unless the project design specifically relies on that approach. Drains can become clogged, damaged, disconnected, overwhelmed, or deprived of a functional discharge point.
Structural resistance to hydrostatic uplift and lateral soil or water pressure is the responsibility of the project design professional. A membrane can resist water passage, but it does not make an inadequately designed structure capable of resisting structural loads.
Positive-Side, Negative-Side, and Blind-Side Installation
The membrane location changes how the system performs and how it must be installed.
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Positive-side waterproofing: The membrane is placed on the side from which water is expected. This arrangement generally prevents water from entering the structure and allows water pressure to push the membrane toward its supporting substrate.
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Negative-side waterproofing: The material is installed on the side opposite the water source. Water may enter the substrate before reaching the waterproofing layer, and hydrostatic pressure may act to separate the material from the surface. Only products and details specifically approved for negative-side exposure should be used.
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Blind-side waterproofing: The waterproofing is installed against lagging, shoring, mud slabs, or other surfaces before the structural concrete is placed. Access for later inspection or repair is extremely limited, and the system must be designed for the specific construction sequence.
A product suitable for conventional positive-side installation should not be assumed suitable for blind-side or negative-side use.
Foundation Walls
Vertical foundation walls commonly include form-tie holes, bugholes, fins, honeycombing, cold joints, lift lines, pipe penetrations, changes in plane, and transitions to footings or slabs. These conditions must be corrected and detailed before the general membrane application.
At the wall-to-footing transition, the membrane must remain continuous across the change in plane and connect to the specified horizontal waterproofing, waterstop, or other termination detail. Sharp inside corners may require an approved cant, fillet, sealant, reinforcement, or liquid flashing treatment.
The completed wall membrane must be protected before backfilling. Soil, stone, construction debris, compaction equipment, and drainage-board fasteners can puncture or displace an unprotected membrane.
Slabs and Foundations
Waterproofing beneath a slab may be installed over a mud slab, prepared compacted substrate, or another approved working surface. The surface must be sufficiently stable, smooth, clean, and dry for the selected system.
Particular attention is required at:
- Slab-to-wall and slab-to-footing transitions
- Pile caps, grade beams, and foundation steps
- Construction and expansion joints
- Pipe, conduit, drain, and grounding penetrations
- Sumps, elevator pits, and depressed areas
- Membrane terminations and connections to waterstops
Horizontal membranes must be protected from reinforcing steel, chairs, worker traffic, concrete placement equipment, and dropped tools. A protection course should be installed as specified and inspected before subsequent construction begins.
Pits, Sumps, and Trenches
Pits and trenches combine many of the most demanding waterproofing details within a confined area. They frequently include inside and outside corners, floor-to-wall transitions, drains, embedded steel, pipe penetrations, equipment anchors, joints, and low points where water can collect.
The contractor must also determine whether the structure is exposed only to groundwater or whether it will contain process water, chemicals, fuels, wastewater, cleaning solutions, or elevated temperatures. A waterproofing membrane is not automatically a chemical-resistant lining.
When chemical containment is required, the system must be selected for both the external waterproofing exposure and the internal service environment. Different systems may be required on opposite sides of the structure.
Confined-Space and Excavation Hazards
Pits, tanks, vaults, trenches, and excavations can introduce serious hazards that are separate from the coating operation. These may include engulfment, collapse, hazardous atmospheres, limited entry and exit, poor ventilation, falls, water accumulation, and exposure to vapors from primers, solvents, or membrane materials.
Before work begins, the employer must determine which OSHA excavation, trenching, respiratory-protection, ventilation, and permit-required confined-space requirements apply. A membrane application procedure is not a substitute for the employer's site-specific safety program.
Surface Preparation and Pre-Application Inspection
Before priming or applying the membrane, inspect the substrate for:
- Unsound concrete, honeycombing, spalls, voids, and exposed reinforcement
- Form-release agents, curing compounds, laitance, dirt, mud, oil, and other contamination
- Projections, fins, sharp edges, and abrupt surface irregularities
- Active water leakage or saturated areas
- Cracks and joints that have not received the specified treatment
- Incomplete penetration, waterstop, termination, or transition details
- Surface moisture and environmental conditions outside product limitations
ASTM D5295/D5295M provides guidance for preparing concrete surfaces for adhered waterproofing membranes. The manufacturer's requirements and project specification determine the final acceptance criteria.
Terminations and Transitions
Below-grade leakage often develops where one material, plane, or construction phase meets another. Critical transitions may include:
- Below-grade membrane to above-grade wall system
- Vertical wall membrane to under-slab membrane
- New construction to an existing structure
- Fluid-applied membrane to sheet membrane
- Waterproofing to waterstops or joint systems
- Membrane around sleeves, pipes, conduits, and drains
- Membrane termination at grade, parapets, curbs, and equipment bases
Every transition should have an approved detail showing substrate preparation, overlap, reinforcement, sealant, fastening, termination height, and compatibility. Do not improvise concealed transitions in the field.
Drainage and Protection
Drainage materials collect and direct water toward an approved discharge point. Protection materials shield the cured membrane from damage during backfilling and subsequent construction. A drainage board may perform both functions only when the approved assembly identifies it for both purposes.
Verify that drainage and protection materials:
- Are chemically and physically compatible with the membrane
- Do not require prohibited fasteners through the waterproofing
- Remain secure during backfilling or concrete placement
- Are oriented and terminated correctly
- Connect to a functioning drain or discharge system
- Do not create unsupported gaps, sharp edges, or concentrated loads against the membrane
ASTM D7492/D7492M provides guidance concerning drainage-system media used with waterproofing systems.
Backfilling Is a Controlled Construction Operation
Backfilling should not begin until the membrane has cured, passed the required inspection or testing, and received its specified protection. Coordination with the excavation or general contractor is essential.
- Remove debris, sharp stone, reinforcing-wire scraps, and discarded materials from the excavation.
- Confirm that protection board and drainage components are secure.
- Prevent equipment from striking the wall or dragging material against the assembly.
- Place and compact backfill in the specified lifts and sequence.
- Monitor the membrane assembly during the operation.
- Stop work and document any displacement or suspected damage.
Inspection Before Concealment
- Verify that the approved system and current product instructions were used.
- Inspect the membrane for pinholes, holidays, thin areas, runs, sags, blisters, contamination, and mechanical damage.
- Confirm the specified wet- and dry-film thickness requirements.
- Inspect every corner, joint, penetration, termination, and transition.
- Perform specified adhesion, flood, electronic leak-detection, or other acceptance testing.
- Repair defects using the manufacturer's approved procedure.
- Reinspect and document the repairs.
- Obtain acceptance before installing protection, covering the membrane, or backfilling.
Documentation for Below-Grade Work
Because the completed membrane will be concealed, documentation becomes especially important. The project record should include:
- Approved product data, details, and application procedures
- Substrate-condition and moisture records
- Environmental readings
- Product names, batch numbers, and quantities
- Application dates, coat locations, and thickness measurements
- Detail, penetration, termination, and transition photographs
- Inspection and testing results
- Repair locations and corrective procedures
- Written authorization to cover or backfill the completed system
Photographs should show the location and context of the work rather than only close-up views that cannot later be identified.
Technical References
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ASTM C836/C836M-18(2022)
— Standard Specification for High-Solids-Content, Cold Liquid-Applied Elastomeric Waterproofing Membrane for Use with Separate Wearing Course.
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ASTM C1471/C1471M-22
— Standard Guide for the Use of High-Solids-Content Cold Liquid-Applied Elastomeric Waterproofing Membrane on Vertical Surfaces.
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ASTM D7832/D7832M-24
— Standard Guide for Performance Attributes of Waterproofing Membranes Applied to Below-Grade Walls and Vertical Surfaces Enclosing Interior Spaces.
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ASTM D5295/D5295M-18
— Standard Guide for Preparation of Concrete Surfaces for Adhered Membrane Waterproofing Systems.
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ASTM D7492/D7492M-16a(2024)
— Standard Guide for Use of Drainage System Media with Waterproofing Systems.
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Whole Building Design Guide—Foundation Walls
— Below-grade enclosure guidance addressing waterproofing, drainage, protection, waterstops, and foundation-wall design.
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The waterproofing manufacturer's current product data sheets, safety data sheets, approved details, application instructions, compatibility requirements, and written project-specific technical guidance.
Confirm the current edition and contractual applicability of every standard before use. Referenced standards provide technical guidance but do not replace the project drawings, specifications, applicable codes, or the manufacturer's written requirements.
Professional responsibility: Do not cover or backfill a below-grade membrane until the installation has been inspected, required testing has been completed, defects have been repaired, and the work has been accepted. When site conditions differ from the drawings or approved details, stop the affected work and obtain written direction before proceeding.
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