How to Write a Performance-Based Waterproofing Specification: A Consultant’s Guide
A good waterproofing specification should do more than name a product.
It should clearly define the performance required from the complete waterproofing system.
Too often, waterproofing specifications are written in broad terms such as:
“Apply two coats of approved waterproofing membrane.”
This may appear simple, but it leaves many important questions unanswered.
- What substrate preparation is required?
- What membrane thickness is acceptable?
- How should joints be treated?
- How should pipe penetrations be waterproofed?
- Is reinforcement required?
- How should the membrane terminate?
- What testing is required?
- What happens if the contractor proposes an alternative product?
Without clear requirements, different contractors may price completely different systems while claiming to comply with the same specification.
At Topkrete, our principle is:
A waterproofing specification should define performance, detailing and execution—not simply a product name.
What Is a Performance-Based Waterproofing Specification?
A performance-based specification defines what the waterproofing system must achieve, while also setting minimum technical and installation requirements.
Instead of only stating:
“Use approved waterproofing membrane.”
a stronger specification may define:
- Application area
- Exposure condition
- Waterproofing type
- Minimum dry-film thickness or membrane thickness
- Crack-bridging requirement
- Adhesion requirement
- UV resistance
- Chemical resistance
- Hydrostatic-pressure resistance
- Joint treatment
- Penetration detailing
- Testing
- QA/QC
- Warranty
- Approved applicator requirements
This gives the contractor a much clearer basis for tendering.
Why Product-Only Specifications Create Problems
When a specification is based only on a product name, several problems can arise.
These include:
- Unequal tender comparison
- Material substitution
- Reduced membrane thickness
- Different application rates
- Missing joint treatment
- Missing reinforcement
- Poor detailing
- Unclear testing requirements
- Disputes during construction
Two products may appear similar but have very different:
- Thickness
- Solids content
- Elongation
- Crack-bridging ability
- Chemical resistance
- UV resistance
- Adhesion
- Service limitations
Therefore, the specification should explain why the material is required and what performance it must achieve.
1. Start With the Waterproofing Application
The first step is to clearly identify where the waterproofing will be used.
Typical applications include:
- Roofs
- Podium decks
- Basements
- Retaining walls
- Toilets
- Balconies
- Planter boxes
- Water tanks
- Swimming pools
- Plant rooms
- Data centres
- Industrial facilities
Different areas have different risk profiles.
A waterproofing system suitable for a toilet may not be suitable for a basement under hydrostatic pressure.
Consultant Principle
The specification should be application-specific, not generic across the entire project.
2. Define the Water Exposure
Before defining the material, define the water condition.
Ask:
- Is the area exposed to rain?
- Is continuous immersion expected?
- Is hydrostatic pressure present?
- Is the system exposed to UV?
- Is chemical exposure expected?
- Is the waterproofing positive side or negative side?
- Will water pressure increase with depth?
These conditions determine the performance requirement.
3. Define the Waterproofing Type
The consultant should identify the general waterproofing technology appropriate for the application.
Examples include:
- Cementitious waterproofing
- Flexible cementitious waterproofing
- Polyurethane membrane
- Acrylic membrane
- Bituminous membrane
- TPO membrane
- PVC membrane
- HDPE membrane
- Crystalline waterproofing
- Bentonite waterproofing
Where appropriate, equivalent technologies may be permitted, subject to technical compliance.
4. Specify Minimum Thickness
Thickness is one of the most important waterproofing parameters.
For liquid-applied systems, consultants should define:
- Minimum wet-film thickness
- Minimum dry-film thickness
- Number of coats
- Application rate where relevant
For sheet membranes, define:
- Nominal membrane thickness
- Reinforcement requirements
- Seam width
- Overlap requirements
A specification that only states “two coats” may be insufficient.
Two very thin coats can still fail to achieve the required thickness.
Consultant Principle
Specify measurable thickness—not only the number of coats.
5. Define Surface Preparation
Good waterproofing depends heavily on substrate preparation.
The specification should address:
- Concrete curing
- Surface cleanliness
- Removal of laitance
- Oil contamination
- Dust
- Loose material
- Honeycombing
- Surface cracks
- Moisture condition
- Surface profile
- Repair mortar
A high-performance membrane applied over a weak substrate may fail by delamination.
Important Principle
Waterproofing adhesion is only as strong as the surface to which it is bonded.
6. Specify Crack Treatment
Cracks should not be left to general interpretation.
The specification should distinguish between:
- Hairline cracks
- Static cracks
- Active cracks
- Structural cracks
- Construction joints
- Expansion joints
Possible treatments may include:
- Resin injection
- Flexible sealants
- Reinforcement bands
- Crack-bridging membranes
- Joint tapes
- Structural repair
Structural cracks should be reviewed by the structural engineer before waterproofing.
7. Define Construction-Joint Treatment
Construction joints are critical waterproofing interfaces.
The specification should identify whether the joint requires:
- PVC/TPE waterstop
- Hydrophilic waterstop
- Crystalline treatment
- Injection hose
- Surface membrane reinforcement
- Joint sealant
The detail should be coordinated with the structural drawings.
Consultant Consideration
Do not simply write:
“Waterproof all construction joints.”
Define how.
8. Define Expansion-Joint Treatment
Expansion joints are designed to move and must be treated differently from normal concrete cracks.
The specification should define:
- Expected joint movement
- Joint width
- Flexible joint system
- Waterproofing band
- Mechanical profile
- Sealant
- Secondary waterproofing
The waterproofing system must allow movement without losing continuity.
9. Detail Pipe Penetrations
Pipe penetrations should have dedicated details.
The specification may need to address:
- Pipe sleeve
- Annular seal
- Waterproofing collar
- Reinforcement
- Sealant
- Mechanical flashing
- Puddle flange
This is particularly important for:
- Basement walls
- Roofs
- Water tanks
- Plant rooms
Important Principle
Every penetration should be treated as a waterproofing interface.
10. Define Waterproofing Upstands
The specification should clearly state where waterproofing must continue vertically.
Typical locations include:
- Parapets
- Walls
- Door thresholds
- Equipment plinths
- Planter walls
The upstand height should relate to:
- Final finished level
- Expected water level
- Drainage
- Splash exposure
A nominal height without coordination with finishes can become ineffective.
11. Define Membrane Terminations
The upper edge of the waterproofing system must prevent water from travelling behind the membrane.
Depending on the system, the specification may require:
- Termination bars
- Recessed chases
- Flashing
- Counter flashing
- Compatible sealants
- Mechanical fixing
The termination detail should be shown clearly on drawings.
12. Define Reinforcement Requirements
Some waterproofing systems require reinforcement at selected areas.
These may include:
- Corners
- Cracks
- Joints
- Penetrations
- Changes in level
- Drain outlets
The specification should state:
- Reinforcement type
- Width
- Location
- Installation method
Do not leave reinforcement entirely to applicator discretion unless specifically intended.
13. Define Primer Requirements
Where a primer is required, the specification should state:
- Primer type
- Substrate condition
- Application rate
- Drying time
- Compatibility
Using an incorrect primer can affect adhesion.
Some systems may not require primer under certain conditions, while others depend heavily on it.
14. Define Protection
Waterproofing can be damaged after installation by other trades.
Protection may include:
- Protection board
- Screed
- Geotextile
- Drainage board
- Protective topping
- Walk pads
The specification should also identify who is responsible for protecting completed waterproofing.
This is important during:
- Backfilling
- Tiling
- Equipment installation
- Landscaping
- M&E works
15. Define Drainage Requirements
Waterproofing and drainage should work together.
The specification and drawings should coordinate:
- Falls
- Outlets
- Overflow drains
- Drainage channels
- Planter drainage
- Drainage boards
Waterproofing should not be expected to compensate for poor water management.
16. Specify Testing Requirements
Testing should be defined before tender.
Depending on the waterproofing system, testing may include:
- Ponding test
- Flood test
- Electronic leak detection
- Seam probing
- Spark testing
- Adhesion testing
- Thickness measurement
- Visual inspection
The specification should define:
- Test method
- Test duration
- Acceptance criteria
- Responsibility
- Repair and retesting
Consultant Principle
If testing is important, include it in the tender specification—not after leakage occurs.
17. Specify QA/QC Requirements
A good waterproofing specification should include quality-control requirements.
These may include:
- Approved applicator
- Supervisor qualification
- Pre-installation meeting
- Substrate inspection
- Mock-up
- Material batch records
- Thickness checks
- Daily installation records
- Photographic documentation
- Final inspection
These requirements improve accountability.
18. Define Material Compatibility
Waterproofing systems often interface with:
- Sealants
- Primers
- Adhesives
- Insulation
- Tiles
- Screeds
- Flashings
- Metal surfaces
- Other membranes
The specification should ensure these materials are compatible.
Two individually good products can still fail if their interface is poorly designed.
19. Define Applicator Requirements
Waterproofing performance depends greatly on workmanship.
The specification may require the contractor to use:
- Manufacturer-approved applicators
- Trained installation personnel
- Qualified welding personnel for TPO/PVC
- Experienced injection technicians
This is particularly important for:
- Single-ply membranes
- Injection works
- Expansion joints
- Complex detailing
20. Control Product Substitution
“Or equivalent” is common in specifications.
But equivalence should not be determined by price alone.
Alternative products should be required to demonstrate compliance with key performance criteria.
These may include:
- Membrane thickness
- Tensile strength
- Elongation
- Crack bridging
- Adhesion
- UV resistance
- Chemical resistance
- Water-pressure resistance
- Relevant certification
- Warranty
- Track record
Consultant Principle
Equivalent should mean technically equivalent—not merely similar in description.
21. Define Warranty Requirements Carefully
Warranty requirements should be clear and realistic.
The specification should identify:
- Warranty period
- Party providing warranty
- Scope
- Exclusions
- Maintenance obligations
- Consequential limitations
- Repair obligations
Consultants should avoid relying on warranty as a substitute for proper design.
Important Principle
A long warranty cannot compensate for a poorly designed waterproofing system.
22. Consider Maintainability
A good waterproofing specification should also consider what happens after handover.
Ask:
- Can the membrane be inspected?
- Can leaks be located?
- Can damaged areas be accessed?
- Can joints be repaired?
- Can membranes be replaced?
- Are walkways provided?
This is especially important for:
- Data centres
- Green roofs
- Podiums
- Buried basement membranes
- Roofs with heavy equipment
Prescriptive vs Performance-Based Specification
There are generally two common approaches.
Prescriptive Specification
This tells the contractor exactly what to install.
Example:
“Apply Product X at 1.5 mm dry-film thickness.”
Advantages:
- Easy to understand
- Easier quality control
- Consistent tendering
Limitations:
- May restrict competition
- May rely too heavily on one material
Performance-Based Specification
This defines required performance.
Example:
“Provide a flexible waterproofing membrane achieving the specified dry-film thickness, crack-bridging performance, adhesion and water-resistance requirements.”
Advantages:
- Allows technically compliant alternatives
- Encourages system comparison
Limitations:
- Requires stronger technical evaluation
- Alternatives must be carefully reviewed
Best Practice
For many projects, a combination works well:
Define the required system and performance, then list approved products or approved equivalents.
Example of a Weak Waterproofing Specification
“Apply two coats of approved waterproofing to all wet areas.”
This specification does not define:
- Product technology
- Thickness
- Surface preparation
- Reinforcement
- Upstand
- Penetration treatment
- Testing
- Protection
Example of a Stronger Waterproofing Specification
“Provide a complete flexible waterproofing system to designated wet areas, including substrate preparation, crack and joint treatment, compatible primer where required, membrane applied to the specified minimum dry-film thickness, reinforcement at corners and penetrations, continuous waterproofing upstands, termination detailing, protection and ponding testing before covering. Materials shall be installed in accordance with approved technical data and project requirements.”
The exact technical parameters should then be added according to the selected system.
Example – Basement Specification Structure
A basement waterproofing specification may include:
Part 1 – Performance Requirements
- Hydrostatic resistance
- Design water exposure
- Required system type
Part 2 – Materials
- Membrane
- Crystalline treatment
- Waterstop
- Hydrophilic strip
- Injection hose
Part 3 – Detailing
- Raft-to-wall joint
- Construction joints
- Pipe penetrations
- Lift pits
Part 4 – Execution
- Surface preparation
- Installation
- Protection
Part 5 – QA/QC
- Inspection
- Testing
- Records
This creates a much clearer tender package.
Example – TPO/PVC Roof Specification Structure
A single-ply roofing specification should consider:
- Structural deck
- Vapour control
- Insulation
- Cover board
- Membrane thickness
- Membrane reinforcement
- Fastening or adhesion
- Wind-uplift requirements
- Seam welding
- Penetration details
- Walkways
- Drainage
- Testing
- Roof-system approval where required
Do not specify only:
“1.5 mm TPO roofing.”
The membrane is only one part of the roof assembly.
Consultant Waterproofing Specification Checklist
Before issuing a waterproofing specification for tender, check:
- Application area is clearly defined.
- Water exposure is understood.
- Waterproofing technology is appropriate.
- Minimum membrane thickness is stated.
- Surface preparation is specified.
- Crack treatment is defined.
- Construction joints are detailed.
- Expansion joints are detailed.
- Pipe penetrations are addressed.
- Upstand requirements are defined.
- Membrane terminations are detailed.
- Reinforcement requirements are stated.
- Primer requirements are defined.
- Protection is included.
- Drainage is coordinated.
- Testing requirements are specified.
- QA/QC requirements are included.
- Applicator requirements are defined.
- Product substitution criteria are established.
- Warranty requirements are realistic.
- Future maintenance is considered.
Why Better Specifications Produce Better Tenders
A clear waterproofing specification does more than improve technical quality.
It also improves tender comparison.
When all bidders are required to price:
- The same membrane thickness
- The same joint treatment
- The same testing
- The same protection
- The same detailing
- The same QA/QC
the consultant can compare quotations more fairly.
Without clear requirements, the lowest tender may simply contain the least waterproofing.
Consultant Principle
A good waterproofing specification creates technical clarity before price comparison begins.
Waterproofing Should Not Be Left Entirely to the Contractor
Contractor expertise is valuable, but the consultant should define the minimum design intent.
If the waterproofing system is decided only after award, several risks may arise:
- Budget pressure
- Material downgrade
- Inconsistent details
- Late coordination
- Variation claims
- Disputes over scope
Early waterproofing design allows the consultant to coordinate:
Architecture + structure + M&E + drainage + waterproofing.
This creates a stronger project outcome.
TOPKRETE Specification Support Approach
Topkrete recommends the following process when assisting consultants.
Step 1 – Understand the Project
Review:
- Building type
- Waterproofing areas
- Water exposure
- Construction method
Step 2 – Identify Critical Risks
Review:
- Joints
- Penetrations
- Movement
- Drainage
- Access
Step 3 – Recommend the System
Select appropriate technologies for each area.
Step 4 – Develop Technical Details
Prepare:
- Typical details
- Joint details
- Penetration details
- Upstands
- Terminations
Step 5 – Develop the Specification
Define:
- Materials
- Performance
- Thickness
- Execution
- Testing
- QA/QC
Step 6 – Review Alternatives
Evaluate technical compliance before approving substitutions.
Conclusion
A waterproofing specification should not simply tell the contractor what product to purchase.
It should define:
What the system must achieve, how it should be installed and how its performance will be verified.
A strong specification coordinates:
Material + substrate + joints + penetrations + thickness + detailing + protection + testing + QA/QC.
The clearer these requirements are before tender, the lower the risk of misunderstanding, cost-driven substitution and future leakage.
At Topkrete, our philosophy remains:
Waterproofing is a system, not a product.
And a good specification is what turns that system from a design intention into a clear construction requirement.
Need Assistance Preparing a Waterproofing Specification?
Topkrete provides technical specification support to architects, engineers, developers and consultants during the design and tender stages.
Our technical team can assist with:
- Performance-based waterproofing specifications
- Roof waterproofing specifications
- Basement waterproofing specifications
- TPO/PVC roofing specifications
- Crystalline waterproofing specifications
- Water-tank waterproofing
- Construction-joint details
- Waterproofing drawing review
- Product comparison
- Tender technical requirements
- Method statements
- Project-specific technical proposals
TOPKRETE SDN BHD
Waterproofing • Resin Flooring • Protective Coatings
Website: www.topkrete.com
Email: info@topkrete.com