One of the most common misunderstandings in waterproofing is the assumption that once a membrane or coating has been applied, cracks and structural movement will no longer be a problem.
In reality, buildings continue to move throughout their service life.
Concrete shrinks. Structures deflect. Temperature changes cause expansion and contraction. Different materials move at different rates. Joints open and close. Equipment can introduce vibration. Settlement may occur over time.
If the waterproofing system is not designed to accommodate the expected movement, leakage may eventually develop even when the original application was properly carried out.
At Topkrete, we consider crack behaviour and structural movement as part of the waterproofing design from the beginning.
Waterproofing must work with the structure, not against it.
Why Structural Movement Matters
Concrete may appear rigid, but it is not completely static.
Movement can result from:
- Drying shrinkage
- Thermal expansion and contraction
- Structural loading
- Deflection
- Settlement
- Differential movement
- Vibration
- Construction sequencing
- Creep
- Changes in moisture condition
Some movements are very small.
Others may be large enough to create visible cracks or open existing joints.
The critical issue for waterproofing is not simply whether a crack exists.
The more important question is:
Is the crack stable, or is it still moving?
This distinction directly affects how the waterproofing detail should be designed.
Not All Cracks Are the Same
A common mistake is to treat every crack using the same repair method.
For waterproofing design, cracks should first be understood according to their behaviour.
They may generally be classified as:
- Static cracks
- Active or moving cracks
- Shrinkage cracks
- Structural cracks
- Construction joints
- Control joints
- Expansion joints
Each requires a different design approach.
1. Static Cracks
A static crack is generally one that is no longer expected to experience significant movement.
These may sometimes be repaired using appropriate materials such as:
- Epoxy injection
- Resin repair
- Polymer-modified repair mortar
- Compatible sealant
- Crack-filling compounds
The correct method depends on:
- Crack width
- Crack depth
- Structural condition
- Water pressure
- Accessibility
- Waterproofing system
Once repaired, the waterproofing system can usually be reinstated over the repaired area, subject to the manufacturer’s requirements.
Consultant Consideration
Before specifying crack repair, determine whether the crack is truly stable.
Repairing an active crack as though it were static may only transfer the problem to another location.
2. Active or Moving Cracks
Active cracks continue to open and close due to structural or thermal movement.
This presents a greater challenge.
A rigid waterproofing material applied directly across an active crack may eventually split.
In such conditions, the waterproofing design may require:
- Flexible crack-bridging membranes
- Reinforcement layers
- Joint bands
- Elastomeric sealants
- Movement-compatible systems
- Special transition detailing
The required solution depends on the magnitude and frequency of movement.
Important Principle
The waterproofing system must accommodate the expected movement, not merely cover the existing crack.
3. Shrinkage Cracks
Shrinkage cracking is common in concrete.
It can occur due to:
- Moisture loss
- Concrete mix design
- Curing conditions
- Large pour sizes
- Restraint
- Temperature changes
Some shrinkage cracks may remain very small and stable.
Others may widen or become pathways for water.
For waterproofing applications, consultants should consider:
- Expected crack width
- Whether the crack is active
- Membrane crack-bridging capability
- Reinforcement requirements
- Whether joint detailing is needed
Large areas such as podium decks and roofs should be reviewed carefully because shrinkage movement can occur across long distances.
4. Structural Cracks
Structural cracks require greater attention.
These may be associated with:
- Excessive loading
- Settlement
- Deflection
- Structural distress
- Movement at supports
- Design or construction issues
Waterproofing should not be used to hide or compensate for an unresolved structural problem.
If the crack is potentially structural, the structural engineer should first assess:
- Cause of cracking
- Structural significance
- Stability
- Repair requirement
- Expected future movement
Only after the structural condition is understood should the waterproofing repair be finalized.
Consultant Consideration
Waterproofing treatment should follow structural assessment, not replace it.
5. Construction Joints
Construction joints are intentional interruptions in concrete placement.
They may be necessary because of:
- Pour sequence
- Work schedule
- Concrete volume
- Structural layout
However, construction joints are also common pathways for water.
Movement may occur at these joints because the concrete on each side was placed at different times.
Depending on the structure, waterproofing measures may include:
- Cast-in waterstops
- Hydrophilic waterstops
- Crystalline treatment
- Injection hose systems
- Joint sealants
- Surface-applied membranes
- Reinforcement at membrane level
Construction joints should therefore be coordinated between the structural and waterproofing designs.
6. Control Joints
Control joints are intentionally created to manage where cracking occurs.
Their purpose is to allow the structure or screed to crack in a controlled location.
A common waterproofing mistake is to apply a rigid membrane continuously across a control joint without considering the movement.
Where movement is expected, the waterproofing system should include a detail capable of accommodating it.
This may involve:
- Flexible joint bands
- Sealants
- Reinforcement
- Decoupling details
- Compatible membrane systems
The joint must remain functional while still maintaining waterproofing continuity.
7. Expansion Joints
Expansion joints are specifically designed to accommodate movement.
They may open, close, shear or move vertically.
These joints should not be treated as ordinary cracks.
A suitable waterproofing expansion-joint system should consider:
- Joint width
- Total expected movement
- Direction of movement
- Water pressure
- Traffic exposure
- Chemical exposure
- UV exposure
- Service temperature
- Accessibility for replacement
Depending on the application, the system may include:
- Elastomeric joint bands
- Expansion joint profiles
- Compression seals
- Sealants
- Mechanical fixing systems
- Waterstops
- Secondary waterproofing layers
Consultant Consideration
Expansion-joint waterproofing should be designed as a specialized component of the overall waterproofing system.
Crack Bridging – What Does It Mean?
Many waterproofing products are described as having crack-bridging capability.
However, this term should not be interpreted as meaning the membrane can accommodate unlimited structural movement.
Crack-bridging performance depends on factors such as:
- Membrane thickness
- Material elasticity
- Temperature
- Reinforcement
- Crack width
- Movement frequency
- Substrate condition
Consultants should therefore review the actual tested performance of the proposed system rather than relying only on general marketing descriptions.
A system that can bridge a small static crack may not be suitable for an active movement joint.
Waterproofing Over Screeds
Another common issue occurs when waterproofing is applied over cementitious screeds.
Screeds can crack due to:
- Drying shrinkage
- Insufficient curing
- Excess water
- Large bay size
- Lack of control joints
- Differential movement from the structural slab
If the waterproofing membrane is bonded directly to the screed, cracks in the screed may transfer through the membrane.
Consultants should therefore consider:
- Screed design
- Bay sizes
- Control joints
- Moisture condition
- Surface preparation
- Membrane flexibility
Waterproofing should not be expected to compensate for poorly designed or unstable screeds.
Waterproofing at Different Materials
Movement often occurs where different construction materials meet.
Examples include:
- Concrete to brickwork
- Concrete to steel
- Concrete to precast elements
- Wall to floor
- Roof slab to parapet
- Pipe to concrete
- Metal frame to masonry
Different materials have different coefficients of thermal expansion and different movement characteristics.
These junctions should be treated as potential movement locations.
Depending on the application, additional reinforcement or flexible detailing may be required.
Temperature and Exterior Waterproofing
Exterior waterproofing systems are especially affected by temperature changes.
Roof surfaces may experience significant temperature differences between:
- Day and night
- Sunny and cloudy conditions
- Wet and dry weather
This creates expansion and contraction in the substrate and waterproofing system.
Dark-coloured exposed roof surfaces may become particularly hot under direct sunlight.
Consultants selecting an exposed waterproofing system should therefore consider:
- UV resistance
- Thermal stability
- Elongation
- Crack-bridging ability
- Movement joints
- Surface temperature
The waterproofing system should be suitable for the actual environment in which it will operate.
Basement Movement and Hydrostatic Pressure
Movement becomes even more critical in basement waterproofing because water may be under hydrostatic pressure.
A small crack that might cause only minor dampness above ground can become a significant leakage point below ground.
Basement waterproofing should therefore consider both:
Structural movement + water pressure.
Particular attention should be given to:
- Raft-to-wall joints
- Construction joints
- Pile interfaces
- Penetrations
- Movement joints
- Lift pits
- Wall cracks
Where the waterproofing cannot be accessed externally after construction, provision for future remedial injection may also be considered.
Should Every Crack Be Filled Before Waterproofing?
Not necessarily with the same material or method.
The correct sequence is:
Identify → investigate → classify → repair/detail → waterproof.
Before treatment, determine:
- What caused the crack?
- Is it structural or non-structural?
- Is it static or active?
- How wide is it?
- Is water currently passing through it?
- What future movement is expected?
- What waterproofing system will be installed?
Only then should the repair method be selected.
Common Design Mistakes
Consultants and project teams should avoid the following assumptions:
Mistake A
“The waterproofing membrane will cover all cracks.”
Not necessarily. The membrane’s crack-bridging capability must match the expected crack movement.
Mistake B
“We can fill every crack with rigid epoxy.”
Rigid repair may be appropriate for some static cracks, but not for joints or active movement.
Mistake C
“Expansion joints can be treated like construction joints.”
No. Expansion joints are designed to move and require movement-compatible detailing.
Mistake D
“Any flexible coating can handle structural movement.”
Flexibility alone does not define the total movement capability of a waterproofing system.
Mistake E
“If the crack is repaired today, it will never return.”
If the underlying cause remains, cracking may recur.
TOPKRETE Design Approach
When reviewing cracking and structural movement, Topkrete recommends the following sequence:
Step 1 – Understand the Structure
Determine where movement is expected.
Step 2 – Identify Joints and Cracks
Map:
- Construction joints
- Expansion joints
- Control joints
- Existing cracks
- Material interfaces
Step 3 – Classify the Movement
Determine whether each condition is:
- Static
- Active
- Structural
- Non-structural
Step 4 – Select the Appropriate Treatment
Choose suitable:
- Repair materials
- Joint systems
- Reinforcement
- Waterproofing membrane
Step 5 – Maintain Waterproofing Continuity
Ensure the completed detailing remains connected to the main waterproofing system.
Consultant Crack and Movement Checklist
Before approving a waterproofing system, review:
- Existing cracks have been identified.
- Crack widths have been assessed.
- Structural cracks have been reviewed by the structural engineer.
- Static and active cracks are distinguished.
- Construction joints are clearly detailed.
- Expansion joints are clearly identified.
- Control joints are coordinated with waterproofing.
- Membrane crack-bridging capability is appropriate.
- Additional reinforcement is specified where required.
- Changes between different substrate materials are addressed.
- Screed movement has been considered.
- Thermal movement has been considered for exposed systems.
- Hydrostatic pressure has been considered for underground structures.
- Future access and repair options have been reviewed.
Waterproofing Cannot Stop Structural Movement
This is one of the most important principles for consultants and building owners.
Waterproofing materials can:
- Seal
- Bridge
- Accommodate
- Protect
- Reduce water ingress
But waterproofing cannot prevent a building from moving.
If the structure moves beyond the capacity of the waterproofing material, failure may occur.
The objective of good design is therefore not to eliminate movement.
It is to:
Understand the expected movement and provide a waterproofing detail capable of accommodating it.
Conclusion
Cracks should never be treated simply as surface defects.
For waterproofing design, consultants must understand why the crack occurred, whether it is still moving and how much movement is expected in the future.
Static cracks, active cracks, construction joints and expansion joints all behave differently.
They should therefore not be treated with one universal solution.
Good waterproofing design coordinates:
Structure + movement + joint detailing + waterproofing material + future maintenance.
At Topkrete, our philosophy remains:
Waterproofing is a system, not a product.
And understanding how the structure moves is an essential part of designing that system.
Need Assistance With Crack, Joint and Waterproofing Details?
Topkrete provides technical support to architects, engineers, developers and specification consultants during the design, tender and construction stages.
Our technical team can assist with:
- Crack treatment recommendations
- Construction-joint waterproofing
- Expansion-joint waterproofing
- Basement waterproofing
- Roof and podium waterproofing
- Flexible waterproofing systems
- Crystalline waterproofing
- TPO/PVC membrane systems
- Waterproofing specifications
- Method statements
- Construction details
- Project-specific technical proposals
TOPKRETE SDN BHD
Waterproofing • Resin Flooring • Protective Coatings
Website: www.topkrete.com
Email: info@topkrete.com