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Industrial Waterproofing and Fluid-Applied Membrane Systems

Article 22 of 24

Rehabilitation of Existing Waterproofing Systems

Rehabilitation is not simply the application of new membrane over an old surface. The contractor must determine what is present, why the existing system is leaking or deteriorating, whether the substrate and remaining membrane are sound, and how the proposed materials will connect to the existing construction. A successful rehabilitation corrects the causes of failure and restores waterproofing continuity—not merely the visible symptoms.

Begin With an Investigation, Not a Product

Selecting a product before investigating the structure can lead to a repair that is incompatible, incorrectly located, or incapable of resisting the actual exposure.

The investigation should address:

• Where water is entering the assembly
• Where water becomes visible inside the structure
• Whether hydrostatic pressure is present
• Whether the original membrane is positive-side, negative-side, or blind-side
• The type and condition of the existing membrane
• The condition of the concrete or masonry substrate
• Whether drainage and discharge systems remain functional
• Movement at cracks, joints, transitions, and penetrations
• How the repaired area will connect to sound existing waterproofing

Gather the Existing Project Information

Obtain as much information as possible before opening the assembly:

• Original drawings and waterproofing specifications
• Approved submittals and manufacturer details
• Construction photographs
• Inspection and testing reports
• Warranty documents
• Previous repair records
• Leak history and weather conditions associated with leakage
• Maintenance, drain-cleaning, pumping, and flooding records

Existing documents may be incomplete or inaccurate. Field conditions must be verified rather than assumed to match the original design.

Map the Leakage

Develop a drawing or marked plan showing:

• Interior leakage and staining locations
• Cracks, joints, drains, penetrations, and transitions
• Blistered, delaminated, or damaged membrane
• Areas of standing water or poor drainage
• Previous repairs
• Wet insulation, protection board, soil, or overburden
• Locations where destructive openings or samples were taken

Remember that water can travel between layers. The location of an interior drip may not be directly beneath or opposite the membrane breach.

Investigation Openings

Selective openings may be needed to identify the installed assembly and determine the extent of deterioration. Openings should be planned, documented, protected from weather, and repaired after the investigation.

An opening may reveal:

• Actual membrane type and thickness
• Number and sequence of installed layers
• Membrane adhesion and condition
• Wet or deteriorated protection, drainage, or insulation
• Concrete cracking, contamination, or deterioration
• Improper transitions or missing details
• Water traveling laterally within the assembly

Identify the Existing Membrane

Do not assume the existing system is correctly identified by its color or appearance. Different chemistries can look similar but respond differently to cleaners, primers, adhesives, solvents, heat, and repair materials.

Identification may require:

• Review of original product records
• Manufacturer assistance
• Removal and examination of representative samples
• Laboratory analysis
• Field compatibility and adhesion testing

Evaluate the Substrate

Existing concrete may have been exposed to water, salts, chemicals, freeze-thaw cycling, corrosion, vibration, cracking, or previous repair materials. The substrate must be capable of supporting the proposed rehabilitation system.

Evaluate:

• Concrete soundness and surface strength
• Spalling, delamination, and honeycombing
• Reinforcement corrosion
• Crack activity and joint movement
• Moisture content and vapor movement
• Soluble salts, oil, grease, biological growth, and chemical contamination
• Compatibility and bond of existing patches and repair materials

ASTM D5295/D5295M provides guidance for preparing new and existing concrete surfaces for bonded waterproofing, including contamination control and evaluation of concrete moisture.

Repair, Recover, or Replace?

Rehabilitation generally follows one of three approaches:

• Localized repair: Used when defects are limited, the surrounding membrane is sound, and a compatible repair can be made with reliable continuity.
• Recover or overlay: A new membrane is applied over a prepared existing system. This approach requires verified adhesion, compatibility, stable existing materials, and approved transition details.
• Removal and replacement: Required when the existing membrane is widely deteriorated, poorly bonded, incompatible, contaminated, wet, incorrectly detailed, or unable to support the proposed system.

An overlay should not be used merely because removal is inconvenient. The remaining system must provide a dependable foundation for the rehabilitation.

When an Overlay Is a Poor Choice

Applying new membrane over the existing system may be inappropriate when:

• Existing adhesion is inconsistent or inadequate.
• Moisture or liquid is trapped beneath the membrane.
• The existing chemistry cannot be identified.
• Compatibility cannot be demonstrated.
• The membrane is brittle, cracked, blistered, soft, or uncured.
• Details and terminations cannot be reliably connected.
• The substrate beneath the membrane requires structural or concrete repair.
• The original failure mechanism will remain active beneath the new membrane.

Compatibility and Adhesion Testing

Compatibility should be established through written manufacturer approval and representative field testing. A successful small patch does not establish system-wide suitability when the existing membrane varies in age, condition, contamination, or exposure.

A test area should reproduce the proposed work, including:

• Cleaning and surface preparation
• Primer or tie coat
• Reinforcement where required
• Proposed membrane thickness
• Actual environmental and curing conditions
• Specified adhesion or compatibility evaluation

ASTM D7234 provides a method for pull-off testing coatings on concrete. When testing an overlay, record every layer through which failure occurs—not only the final numerical value.

Restoring Active Leaks

Active water can prevent surface preparation, concrete repair, primer adhesion, and membrane cure. The approved rehabilitation plan may require temporary pumping, diversion, rapid-setting water-control materials, exterior excavation, drainage correction, or chemical-grout injection.

ASTM D8109 addresses the selection, installation, and inspection of chemical grout used to seal leaks at cracks in concrete walls and slabs.

Chemical injection may stop a leakage path, but it does not automatically repair structural damage, replace missing waterproofing, or correct inadequate drainage.

Transitions Determine Whether the Rehabilitation Is Continuous

The repaired membrane must connect to sound existing waterproofing or another durable water-control component. Critical transitions may include:

• New membrane to existing membrane
• Horizontal membrane to vertical wall waterproofing
• Waterproofing to drains, scuppers, and penetrations
• Below-grade waterproofing to the above-grade wall system
• New construction to existing construction
• Fluid-applied membrane to sheet membrane
• Rehabilitated membrane to joints and waterstops

If the boundaries of the existing membrane cannot be located or exposed, a reliable transition may not be possible without expanding the work area.

Drainage and Water Management

Rehabilitation should address the water-management system surrounding the membrane. Investigate:

• Blocked or damaged foundation drains
• Clogged drainage composites and filter fabrics
• Failed sump pumps or controls
• Landscape irrigation directed toward the structure
• Roof or surface drainage discharged near foundation walls
• Settled backfill and negative surface grading
• Deck drains, overflows, and weep paths obstructed by debris

Installing new membrane while leaving a failed drainage system in place may subject the rehabilitation to unnecessary and unanticipated water pressure.

Phased Rehabilitation

Operating facilities may require waterproofing work to proceed in phases. Each phase must be left watertight and connected to adjacent completed or existing systems.

The phasing plan should define:

• Limits of each work area
• Temporary terminations and weather protection
• How future phases will connect to completed work
• Traffic, access, and protection requirements
• Temporary drainage and water diversion
• Inspection and testing of each phase
• Responsibility for monitoring completed work during later construction

Rehabilitation Work Sequence

1. Complete the condition survey and leakage map.
2. Make investigation openings and obtain samples where required.
3. Identify the existing membrane and complete compatibility testing.
4. Define repair, overlay, and removal areas.
5. Control active leakage and complete structural or concrete repairs.
6. Correct drainage and detail deficiencies.
7. Prepare and inspect the substrate or retained membrane.
8. Complete approved transitions and details.
9. Apply the rehabilitation membrane under controlled conditions.
10. Inspect, test, repair, and retest the completed work.
11. Install protection, drainage, insulation, or overburden.
12. Document and obtain final acceptance.

Testing Rehabilitated Work

Testing may include visual inspection, thickness measurement, adhesion testing, controlled water testing, flood testing, or electronic leak detection. The selected test must be suitable for the membrane and assembly.

ASTM D7877 addresses electronic conductance methods for locating breaches in exposed or covered waterproofing membranes. Electronic testing can be especially useful when the rehabilitated membrane will be concealed beneath overburden.

Repaired test openings and destructive test locations must be reinspected before the membrane is covered.

Rehabilitation Documentation

The final record should include:

• Condition survey and leakage map
• Investigation-opening locations and findings
• Existing-material identification and laboratory results
• Compatibility and adhesion-test results
• Approved repair and transition details
• Removal, repair, and overlay boundaries
• Materials, batch numbers, and application records
• Inspection, testing, repair, and retesting reports
• Photographs before concealment
• Final acceptance and maintenance requirements

Technical References

• ASTM D5295/D5295M-18 — Standard Guide for Preparation of Concrete Surfaces for Adhered Membrane Waterproofing Systems.
• ASTM D8109-25 — Standard Guide for Waterproofing Repair of Concrete by Chemical-Grout Crack Injection.
• ASTM D7877-25 — Standard Guide for Electronic Methods for Detecting and Locating Leaks in Roofing and Waterproofing Membranes.
• ASTM D7234-22 — Standard Test Method for Pull-Off Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.
• The waterproofing manufacturer's current product data sheets, compatibility letters, approved rehabilitation details, testing instructions, repair procedures, and written project-specific technical guidance.

Confirm the current edition and contractual applicability of every referenced standard. Rehabilitation requirements must be based on verified field conditions and the specific existing and proposed materials.

Professional responsibility: Do not recommend an overlay simply because it is faster or less disruptive than removal. Verify the existing membrane, substrate, adhesion, moisture, compatibility, details, and failure mechanism. When those conditions cannot support a dependable rehabilitation, remove and replace the affected system under an approved design.

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