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Water and Wastewater Protective Coating Systems | Article 18 of 24

Resurfacers, Mortars, Elastomeric Membranes, Polyurethane, and Polyurea Systems

Resurfacers rebuild profile, mortars replace lost section, and membrane systems provide protection or limited movement capability. Each material must be selected for its intended function and its place within the complete system.

These Materials Do Not Perform the Same Job

A repair mortar may restore damaged concrete but provide insufficient long-term chemical resistance as the exposed finish. A polymer lining may resist the exposure but lack the thickness or body needed to rebuild deeply deteriorated concrete. A flexible membrane may tolerate limited movement but be inappropriate for severe abrasion or concentrated chemicals.

The system designer must assign each layer a specific function and confirm compatibility among the substrate, repair material, resurfacer, primer, membrane, lining, reinforcement, joint treatment, and finish.

“Elastomeric” Is Not a Chemistry

Elastomeric describes the ability of a material to stretch and recover. It does not identify the resin or binder used to make the product.

Acrylic, polyurethane, polyurea, and other formulated systems may be elastomeric. The specification should identify the actual chemistry, system build, thickness, reinforcement, movement capability, exposure, and required performance—not rely on “elastomeric” as a complete product description.

Establish the Required Function

Before choosing a material, determine what the material must accomplish:

• Replace deeply deteriorated or missing concrete
• Rebuild wall thickness, channels, benches, curbs, or floors
• Fill bugholes, honeycombing, voids, and surface irregularities
• Create slope or restore drainage
• Provide a uniform substrate for a polymer lining
• Resist wastewater or headspace exposure directly
• Bridge limited cracks or tolerate limited movement
• Provide waterproofing or containment
• Resist abrasion, impact, erosion, or thermal cycling
• Reduce shutdown and return-to-service time

Cementitious Repair Mortars

Cementitious repair mortars are commonly used to replace deteriorated concrete, rebuild damaged sections, restore cover over reinforcement, and correct geometry. Products may be designed for horizontal, vertical, overhead, formed, pumped, troweled, or spray-applied placement.

Selection should consider:

• Required placement thickness and number of lifts
• Vertical, overhead, formed, or horizontal orientation
• Bond to the prepared concrete
• Shrinkage and dimensional stability
• Modulus and compatibility with the existing concrete
• Chemical, moisture, abrasion, and temperature exposure
• Cure and permitted time before coating
• Compatibility with the primer and lining system

Do not assume that high compressive strength alone makes a mortar suitable. Excessive stiffness, shrinkage, poor bond, or incompatibility can cause cracking and separation.

Polymer-Modified Cementitious Mortars

Polymer modification can improve selected properties such as bond, flexural performance, workability, and reduced permeability. The actual performance depends on the formulation and proper water or liquid-component addition.

Adding more liquid than specified to make placement easier can reduce strength, increase shrinkage, alter porosity, delay cure, and affect the coating applied over it. Measure components accurately and follow the stated mixing sequence.

Calcium-Aluminate and Specialty Cementitious Materials

Calcium-aluminate, geopolymer, and other specialty cementitious systems may be selected for wastewater rehabilitation, rapid repair, or improved resistance to particular environments.

These products are not interchangeable. Their performance depends on binder chemistry, aggregates, admixtures, placement, cure, exposure, thickness, and whether the material is intended as an exposed protective surface or as a substrate beneath a polymer lining.

Obtain written confirmation of the proposed role and compatibility with the complete system.

Cementitious Resurfacers

A resurfacer is generally used to correct widespread surface irregularity, fill shallow deterioration, close bugholes, restore profile, and create a more uniform substrate for the protective lining.

Resurfacers may be applied by trowel, spray, pump, brush, squeegee, or other approved method. The product must remain within its permitted thickness and orientation.

A resurfacer should not be used to hide active leakage, structural cracks, unsound concrete, corroding reinforcement, unstable previous repairs, or movement joints requiring separate treatment.

Epoxy Mortars and Resinous Resurfacers

Epoxy mortars and resinous resurfacers can provide rapid strength development, strong adhesion, low permeability, and resistance to selected chemicals. They may be useful for localized repairs, coves, transitions, equipment bases, and rapid-return projects.

Important considerations include:

• Substrate moisture limitations
• Primer requirements
• Mixing ratio and aggregate loading
• Exotherm in thick sections or large batches
• Minimum and maximum placement thickness
• Thermal movement and modulus
• Recoat window
• Compatibility with the final lining

A Smooth Surface Is Not Automatically Ready for Lining

Troweled repair materials can develop laitance, curing residue, contamination, gloss, or an excessively smooth finish. The completed repair may require mechanical preparation before primer or lining application.

Verify cure, moisture condition, cleanliness, soundness, surface profile, and recoat requirements. Appearance alone does not establish readiness.

Elastomeric Membranes

Elastomeric membranes may be used where waterproofing, limited crack bridging, flexibility, or movement tolerance is required. Performance depends on the membrane chemistry, thickness, reinforcement, adhesion, exposure, temperature, and movement characteristics.

Selection questions include:

• Is the membrane approved for continuous immersion?
• Is it resistant to the actual wastewater and chemicals?
• Can it tolerate positive-side and negative-side moisture?
• What crack width and movement has the complete installed system demonstrated?
• Does performance change at low or high temperature?
• Is reinforcement required at cracks, joints, corners, and penetrations?
• Can it resist abrasion, cleaning, impact, and hydrostatic exposure?
• How will it terminate and transition to adjacent systems?

Elongation Does Not Equal Crack-Bridging Performance

Elongation is commonly measured on an unbonded test specimen. A membrane bonded to concrete behaves differently because the substrate restrains the film and concentrates strain at the crack.

Evaluate tested crack-bridging performance, temperature, film thickness, crack width, movement rate, fatigue cycles, adhesion, reinforcement, and installation detail. Do not approve a membrane based only on a high elongation percentage.

Polyurethane Membrane and Lining Systems

Polyurethane systems can be formulated for flexibility, abrasion resistance, toughness, chemical resistance, weathering, or immersion. They may be applied as membranes, high-build linings, intermediate layers, or finish coats.

Aromatic and aliphatic polyurethanes have different weathering characteristics. Exterior ultraviolet exposure, color retention, and gloss requirements should be included in selection.

Some polyurethane products are sensitive to moisture during application and cure. Isocyanate-containing materials require appropriate engineering controls, respiratory protection, skin protection, training, and compliance with the safety data sheet and applicable regulations.

Polyurea Membrane and Lining Systems

Polyurea systems can provide rapid cure, high film build, flexibility, toughness, and short return-to-service time. They may be used over concrete, steel, or approved resurfacing systems when properly designed and installed.

Rapid cure places demanding requirements on plural-component proportioning, material temperature, hose temperature, pressure balance, impingement mixing, spray technique, and substrate preparation. Incorrectly proportioned material can harden without achieving the intended physical or chemical properties.

Confirm chemical resistance, immersion approval, primer, moisture limitations, crack-detailing procedure, required thickness, inspection method, and repairability for the exact formulation.

Polyurethane-Polyurea Hybrids

Hybrid systems combine selected polyurethane and polyurea characteristics. They may provide a different balance of reaction speed, flexibility, application tolerance, and cost.

The word “hybrid” does not establish performance. Review the exact formulation’s test data and written suitability for the substrate, exposure, temperature, immersion, movement, cure, and proposed application.

Primers Are System Components

Primers may promote adhesion, wet the surface, seal porosity, reduce outgassing, or isolate one material from another. One primer may not perform all of these functions.

Apply the specified primer within its coverage range and recoat window. Excess primer can puddle or form a weak layer. Insufficient primer can leave porous or dry areas. An expired recoat window may require additional preparation and repriming.

Do not substitute a convenient primer without written system approval.

Reinforcement at Details

Fabric, scrim, mat, tape, or fleece may be required at cracks, cold joints, corners, penetrations, transitions, and changes in substrate. Reinforcement distributes strain and helps establish controlled membrane thickness.

Inspect for:

• Required width, orientation, and overlap
• Complete saturation or embedment
• Wrinkles, bridging, folds, and trapped air
• Dry fibers or resin-starved areas
• Smooth transitions at reinforcement edges
• Specified cover thickness over the reinforcement

Active Joints Require Joint Details

A movement joint should not be filled rigidly and coated continuously unless the approved design specifically permits that treatment. Movement may tear the lining, break the repair material, or transfer cracking into adjacent concrete.

Joint design may include sealant, backer rod, bond breaker, reinforced membrane, waterstop repair, expansion detail, or another engineered treatment. The joint system must be compatible with the lining and the expected chemical, immersion, and movement exposure.

Application Method Matters

Materials may be placed by:

• Hand trowel
• Screed or squeegee
• Pump and hose
• Wet- or dry-process spray equipment
• Conventional or airless spray
• Heated plural-component spray equipment

The method must be approved for the material and capable of producing the required mixing, consolidation, thickness, texture, and continuity on the project’s actual geometry.

Working Time and Cure Are Temperature Dependent

Higher material and substrate temperatures commonly shorten working time and accelerate reaction. Lower temperatures may increase viscosity, slow cure, reduce spray quality, and extend return-to-service time.

Plan batch size, equipment output, crew size, placement sequence, environmental control, and access around the actual temperatures expected during the work.

Quality-Control Mockup

A representative mockup can confirm surface preparation, repair finish, primer behavior, outgassing control, application method, reinforcement, thickness, texture, cure, appearance, and inspection procedure.

Include representative corners, vertical surfaces, penetrations, repairs, and transitions when practical. Once accepted, preserve the mockup as the field standard for production work.

Inspection and Acceptance

Inspection may include:

• Verification of product, batch, shelf life, storage, and conditioning
• Substrate-preparation and moisture acceptance
• Mixing ratios, liquid additions, aggregate loading, and batch times
• Placement thickness and number of lifts or passes
• Reinforcement installation
• Coves, slopes, transitions, penetrations, and terminations
• Cracking, shrinkage, delamination, voids, pinholes, bubbles, runs, and sags
• Cure and recoat-window compliance
• Adhesion or tensile testing when specified
• Holiday testing and repair where applicable

Contractor’s Field Checklist

• Is each material’s function clearly defined?
• Has all unsound concrete been removed?
• Is the material suitable for the repair depth and orientation?
• Are substrate moisture and surface conditions acceptable?
• Are repair, resurfacer, primer, and lining products compatible?
• Are liquid additions and mixing ratios controlled?
• Are active joints and cracks treated by approved details?
• Is reinforcement correctly placed and completely embedded?
• Can environmental conditions be maintained throughout application and cure?
• Are required thickness, cure, inspection, and testing documented?
• Has the completed work been accepted before the next layer or return to service?

Knowledge Check

1. Is an elastomeric membrane a single coating chemistry?

No. Elastomeric describes a performance characteristic. Different resin chemistries can be formulated to provide elastomeric behavior.

2. Why should a membrane not be selected only by its elongation percentage?

Free-film elongation does not establish installed crack-bridging performance. The bonded system’s thickness, reinforcement, temperature, adhesion, crack width, and movement must also be considered.

3. Can a resurfacer be used to conceal active leakage or unsound concrete?

No. Active leakage, structural deterioration, unstable repairs, and unsound concrete must be properly evaluated and corrected before resurfacing.

4. Why is rapid-cure polyurea application technically demanding?

The rapid reaction leaves little tolerance for incorrect proportioning, temperature, pressure, impingement mixing, equipment condition, or spray technique.

Technical References and Further Study

• ACI PRC-546-23, Concrete Repair—Guide. This guide provides recommendations for selecting and applying methods and materials used to repair, protect, and strengthen concrete.
• ACI PRC-546.3-23, Materials Selection for Concrete Repair—Guide.
• ICRI Guideline No. 320.1R-2019, Guide for Selecting Application Methods for the Repair of Concrete Surfaces.
• ICRI Guideline No. 320.2R-2018, Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces.
• AMPP SSPC-Guide 27-2019, Recommended Performance Properties for Liquid-Applied Organic Polymeric Coatings and Linings for Municipal Wastewater Structures.
• AMPP SSPC-PA 14-2021, Application of Thick-Film Polyurea and Polyurethane Coatings to Concrete and Steel Using Plural-Component Equipment.
• AMPP SSPC-SP 13/NACE No. 6-2024, Surface Preparation of Concrete.
• The repair-material and lining manufacturers’ current technical data sheets, safety data sheets, application instructions, compatibility statements, detail drawings, cure requirements, inspection procedures, and written project recommendations.

Standards, products, formulations, and manufacturer requirements may be revised. Confirm the current documents and exact approved system before selecting or installing repair materials, resurfacers, membranes, polyurethane, or polyurea products.

Professional responsibility: This article provides foundational education and does not replace structural evaluation, engineered repair details, an approved protective-system specification, manufacturer instruction, project-specific safety planning, or qualified inspection. Do not conceal changed or defective substrate conditions without written direction.

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