7 Waterproofing Design Mistakes Consultants Should Avoid Before Tender
Technical guidance for architects, engineers, specification consultants and project teams
Waterproofing failures are often blamed on poor workmanship or defective materials. In practice, many problems begin much earlier—during the design and specification stage.
Once a project reaches construction, changing waterproofing details can become difficult, expensive and disruptive. Consultants therefore play a critical role in ensuring that the waterproofing system is properly designed before the tender is issued.
At Topkrete, our approach is simple:
Waterproofing is a system, not a product.
A reliable waterproofing design must consider the structure, water exposure, joints, penetrations, movement, termination details, protection and future maintenance.
Here are seven common waterproofing design mistakes consultants should review before tender.
1. Selecting the Waterproofing Product Before Understanding the Water Exposure
A common mistake is to begin the specification by selecting a waterproofing material.
The correct starting point should be the water exposure and service conditions.
Before selecting a system, consultants should establish:
- Where is the water coming from?
- Is the water pressure positive or negative?
- Is hydrostatic pressure expected?
- Will the waterproofing be permanently submerged?
- Will the area be exposed to sunlight and weather?
- Will the system be covered by screed, tiles, soil or another layer?
- Is chemical exposure expected?
- Is structural movement likely?
- Can the waterproofing be accessed for repair in the future?
Different areas require different waterproofing strategies.
A roof exposed to UV, a basement retaining wall, a water tank and a toilet floor should not automatically use the same waterproofing system.
Consultant Consideration
Define the exposure condition first. Select the waterproofing system second.
2. Concentrating on the Main Waterproofing Area but Ignoring Critical Details
Most waterproofing drawings clearly show the large membrane area.
However, leakage rarely occurs in the middle of an uninterrupted waterproofing surface.
Failures are much more likely to occur at:
- Pipe penetrations
- Floor outlets
- Construction joints
- Expansion joints
- Internal and external corners
- Door thresholds
- Parapet walls
- Roof upstands
- Membrane terminations
- Equipment bases
- Drainage outlets
- Changes in level
A project may contain thousands of square meters of correctly installed waterproofing but still experience serious leakage because of one poorly detailed penetration.
Consultant Consideration
Each waterproofing interface should have a specific construction detail, not simply a note stating “waterproofing to specialist’s recommendation.”
The design drawings should clearly show how the waterproofing starts, changes direction, penetrates the structure and terminates.
A waterproofing system is only as reliable as its weakest detail.
3. Insufficient Waterproofing Upstand and Termination Height
Another frequent design problem is stopping waterproofing too close to the finished floor level.
During heavy rainfall, blocked drainage, ponding, or water splash, the actual water level may rise above the waterproofing termination.
Consultants should pay particular attention to waterproofing heights around:
- Roof parapets
- Balconies
- Toilets and bathrooms
- Planter boxes
- Podium decks
- Plant rooms
- Kitchen areas
- Swimming pools
- Water features
The waterproofing termination should consider both the finished floor level and the possible water exposure during service.
Termination details must also prevent water from traveling behind the membrane.
Consultant Consideration
Do not specify only the horizontal waterproofing area.
Clearly indicate:
Finished floor level → waterproofing upstand → termination detail → protection detail.
4. Ignoring Structural Movement and Crack Behavior
Concrete structures are not completely static.
Movement can occur due to:
- Drying shrinkage
- Thermal expansion and contraction
- Building settlement
- Structural deflection
- Vibration
- Construction sequencing
- Differential movement between materials
Waterproofing systems must therefore be selected according to the expected movement of the substrate.
A treatment suitable for a static hairline crack may not be suitable for an active joint or structural movement.
Consultants should distinguish between:
- Static cracks
- Moving cracks
- Construction joints
- Control joints
- Expansion joints
Each may require a different detailing approach.
Consultant Consideration
Do not expect a waterproofing coating alone to solve every type of crack.
Movement joints require systems specifically designed to accommodate movement.
5. Under-Designing Construction Joints
Construction joints are among the highest-risk locations in underground waterproofing.
Water can travel through:
- Poorly compacted concrete
- Honeycombed areas
- Shrinkage gaps
- Cold joints
- Tie-rod holes
- Defective waterstop installation
For basements, lift pits, retaining walls and water-retaining structures, construction joints should be treated as part of the original waterproofing design.
Depending on project requirements, the joint protection system may include combinations of:
- Cast-in waterstops
- Hydrophilic waterstops
- Crystalline waterproofing treatment
- Joint sealants
- Injection hoses
- Injectable repair provisions
For critical structures, consultants should consider whether a multiple-barrier approach is appropriate.
Consultant Consideration
Do not leave construction-joint waterproofing entirely to site improvisation.
Joint locations and treatment should be clearly established before construction.
6. Designing Waterproofing Without Considering Future Repair
One important question is frequently overlooked during design:
If the waterproofing leaks in five or ten years, how will it be repaired?
This is especially important where waterproofing will later be buried or permanently concealed.
Examples include:
- Basement retaining walls
- Raft foundations
- Podium decks
- Green roofs
- Planter boxes
- Swimming pools
- Data-center roofs
- Areas underneath heavy equipment
Once construction is completed, accessing the waterproofing may require removal of landscaping, screed, finishes, equipment or even structural elements.
Repair costs can therefore be many times higher than the original waterproofing cost.
Consultant Consideration
Waterproofing design should consider not only initial performance but also:
- Accessibility
- Inspection
- Leak detection
- Maintenance
- Repair methodology
- Replaceability
A slightly higher-quality waterproofing design at the beginning can substantially reduce whole-life maintenance risk.
7. Specifying a Waterproofing Product Instead of a Complete Waterproofing System
A specification such as:
“Apply two coats of approved waterproofing membrane.”
is rarely sufficient for a critical waterproofing application.
A complete waterproofing specification should define the entire system.
This should typically include:
- Substrate requirements
- Surface preparation
- Crack and joint treatment
- Primer requirements
- Waterproofing material
- Application rate or membrane thickness
- Reinforcement where required
- Pipe and penetration detailing
- Upstands and terminations
- Protection layer
- Drainage considerations
- Inspection procedures
- Testing requirements
- Repair procedures
- Quality-control requirements
- Warranty requirements
Without these details, contractors may interpret the waterproofing specification differently during tendering.
This can result in inconsistent pricing and, later, disputes over what was originally included.
Consultant Consideration
Specify performance and the complete system—not simply the product name.
A Better Waterproofing Design Approach
Before releasing a waterproofing package for tender, consultants should review the following questions:
- Has the water exposure been clearly identified?
- Is the selected waterproofing system suitable for the application?
- Are construction joints properly detailed?
- Are expansion and movement joints addressed?
- Are all pipe penetrations and outlets detailed?
- Are waterproofing upstands and terminations clearly shown?
- Is the waterproofing compatible with adjoining materials?
- Is the membrane protected from subsequent construction activities?
- Has drainage been properly considered?
- Can the waterproofing be inspected and tested before covering?
- Is there a realistic future repair strategy?
- Are QA/QC requirements included in the specification?
Conclusion
Successful waterproofing begins long before the waterproofing contractor arrives on site.
The best opportunity to prevent leakage is during the design stage, when consultants can coordinate the structural design, architectural details, drainage system and waterproofing requirements as one integrated system.
Small details such as a pipe penetration, construction joint or membrane termination may represent only a small percentage of the total waterproofing area, but they can determine the performance of the entire system.
For this reason, waterproofing should never be approached as simply selecting a coating or membrane.
Waterproofing is a system, not a product.
Need Assistance Reviewing a Waterproofing Design?
Topkrete provides technical support to architects, engineers, developers and specification consultants during the design and tender stages.
Our technical team can assist with:
- Waterproofing system selection
- Waterproofing specifications
- Construction details
- Basement waterproofing solutions
- Roof waterproofing systems
- TPO/PVC membrane systems
- Crystalline waterproofing
- Water-retaining structures
- Method statements
- Technical proposals
- Project-specific waterproofing recommendations
TOPKRETE SDN BHD
Waterproofing • Resin Flooring • Protective Coatings
Website: www.topkrete.com
Email: info@topkrete.com