Waterstops are essential components in modern concrete construction, designed to prevent water migration through joints in liquid-retaining structures. Whether dealing with basement walls, raft foundations, tunnels, canals, or spillways, every construction joint and movement joint in a watertight structure requires a properly selected water bar. The choice of waterstop depends on the nature of the joint, the anticipated movement, and the hydrostatic pressure the structure will face. For a deeper look at the various options available, refer to the Concrete Waterstops Comprehensive Guide that covers selection criteria in greater detail.
Why Waterstops Are Necessary in Construction Joints
Concrete is inherently porous and develops cracks and joints as it cures and settles. Every concrete structure contains construction joints, contraction joints, expansion joints, and movement joints. Without a waterstop placed inside these joints, water will eventually find a path through them, leading to leakage, structural degradation, and costly repairs. Waterstops serve as physical barriers embedded within the joint to block the flow of water.
The following structures commonly require waterstop installation:
- Basement walls and slabs
- Raft foundations used as basement floors
- Subways and tunnels
- Canals and irrigation channels
- Spillway walls and ogee sections
- Water tanks and reservoirs
- Sewage treatment plants
- Swimming pools
- Retaining walls
When watertightness is a project requirement, waterstops are not optional. They work in conjunction with external waterproofing systems to create a continuous barrier. It is important to note that different types of waterstops are not always compatible with one another. For instance, laying a steel water bar alongside a PVC water bar at the same joint is difficult and rarely effective. For more detail on how waterstops integrate with joint waterproofing systems, see Waterstops For Waterproofing Of Construction Joints.
Popular Types of Waterstops and Their Properties
Several types of waterstops are available, and each serves a specific purpose. The selection depends on joint movement, water pressure, chemical exposure, and installation conditions. Below is a comparison of the main categories.
| Waterstop Type | Best Used For | Movement Capacity | Key Advantage |
|---|---|---|---|
| PVC | Expansion joints, movement joints | High | Flexible, cost-effective, corrosion resistant |
| Rubber | High-movement joints, tunnels, dams | Very high | Excellent elasticity, chemical resistance |
| Mild Steel | Construction joints (limited movement) | Low | Low cost, easy to weld |
| Galvanized Steel | Construction joints (corrosive environments) | Low | Corrosion protection, durability |
| Copper | Hydraulic structures, high-head dams | Moderate | Long-term corrosion resistance |
| Bentonite | Construction joints with limited movement | None | Self-healing, swells with moisture |
| Hydrophilic | Pipe penetrations, construction joints | None | Swells on contact with water |
Each waterstop type brings unique performance characteristics, and the choice must account for both the structural design and the environmental conditions at the project site. The Installing Waterstops guide from Construction Specifier offers practical field advice on handling and placement for these different types.
PVC and Rubber Waterstops in Detail
PVC waterstops are the most widely used type in construction. They are lightweight, flexible, and easy to handle on site. Their ability to accommodate structural movement makes them ideal for expansion joints and movement joints. PVC waterstops offer the following advantages:
- High flexibility and elasticity
- High tensile strength
- Very low water absorption
- Resistance to corrosion
- Unaffected by low temperatures and water immersion
- Ability to bear high hydrostatic pressure and shocks
- Weather resistance and excellent long-term durability
Before selecting a PVC waterstop supplier, certain physical property tests should be carried out to verify the material meets project specifications. The following table lists standard test methods applicable to PVC waterstops.
| Property | Test Method |
|---|---|
| Water absorption | ASTM D-570 |
| Tear resistance | ASTM D-624 |
| Specific gravity | ASTM D-792 |
| Hardness Shore A | ASTM D-2240 |
| Tensile strength | ASTM D-638 Type IV |
| Ultimate elongation | ASTM D-638 Type IV |
| 100% modulus | ASTM D-638 Type IV |
| Low temperature brittleness | ASTM D-746 |
| Stiffness in flexure | ASTM D-747 |
| Ozone resistance | ASTM D-1149 |
| Change in hardness Shore A | ASTM D-2240 |
Rubber waterstops are manufactured from natural or synthetic rubber and offer performance characteristics similar to PVC but with even higher elongation and movement accommodation. They are well suited for demanding applications such as dams, reservoirs, diversion tunnels, and chemical processing areas. Rubber waterstops also perform excellently in sewage treatment plants, swimming pools, water tanks, basement areas, underground car parks, retaining walls, and roof slabs. Key features of rubber water bars include:
- Excellent elasticity and flexibility
- High elongation capacity
- Superior movement accommodation for seismic and subsidence events
- Ability to withstand very high hydrostatic heads
- Resistance to abrasion, tearing, corrosion, and chemicals
- Weather and aging resistance
- Excellent sealing effect over long service periods
Installation methods for rubber waterstops follow similar procedures as PVC. Prefabricated intersection pieces are available for complex joint layouts. For more detailed technical information on these flexible waterstop types, the Concrete Waterstops Comprehensive Guide 3 covers specifications and joint design integration.
Metallic Waterstops: Steel and Copper Options
Metallic waterstops serve construction joints where movement is minimal but high strength and durability are required. The main materials used are mild steel, galvanized steel, stainless steel, and copper.
Mild Steel Waterstops
Mild steel waterstops are widely used in general construction because of their low cost and ease of welding for continuity between sections. However, the main disadvantage is corrosion. If water reaches the steel through the construction joint, the water bar will corrode over time. Mild steel water bars cannot be used in expansion joints or movement joints because they lack the elongation capacity needed to accommodate structural movement. PVC and rubber water bars are preferred where movement is expected.
Galvanized Steel Waterstops
Galvanized steel provides additional protection against corrosion through a zinc coating applied to the mild steel substrate. These waterstops are a durable solution for construction joints in environments where moisture exposure is routine. However, like mild steel, galvanized steel water bars are not suitable for expansion or movement joints.
Stainless Steel Waterstops
Stainless steel waterstops are used in special applications, particularly in highly corrosive environments. The cost of stainless steel is significantly higher than mild or galvanized steel, so they are reserved for projects where long-term corrosion resistance is critical and budget allows.
Copper Waterstops
Copper waterstops are not widely used in conventional construction but are employed in special hydraulic structures such as large dams and spillways where very high hydrostatic heads are present. Copper offers excellent long-term resistance to corrosion. In structures designed for service lives exceeding 100 years, such as major dams, copper waterstops are preferred because the water bar cannot be repaired or replaced once the reservoir is in operation. Both PVC and copper waterstops are commonly seen in hydraulic structures for this reason.
Bentonite and Hydrophilic Waterstops
Bentonite waterstops are hydrophilic strips made from bentonite clay that activate when exposed to moisture. They are placed in grooves cut into construction joints. When water reaches the bentonite, it expands to create a compression seal that blocks further water movement. These waterstops cannot be used in expansion or movement joints since they rely on confinement within the joint to function.
Advantages of bentonite waterstops include:
- Activation upon contact with moisture
- Strong and durable seal at relatively low cost
- High water absorption with excellent compression sealing
- Controlled expansion to prevent spalling or cracking of surrounding concrete
- Ability to withstand high water pressure
- Self-healing capability if the seal is disturbed
- Easy joining and lapping
- Non-toxic material
Common applications for bentonite waterstops include pipe penetrations in concrete, construction joints where movement is limited, water containment structures, manholes, elevator pits, tunnels, culverts, dams, water tanks, canals, swimming pools, retaining walls, precast concrete structures, foundations, basements, and slabs.
Hydrophilic waterstops are another swelling type that react directly to water. When moisture reaches the material, it increases in volume and seals the joint. The expansion is carefully controlled so it does not damage the surrounding concrete. These waterstops are installed in joints where no relative movement occurs, such as construction joints and pipe penetrations embedded in concrete walls. Expansion joints and movement joints cannot be made watertight using hydrophilic waterstops alone.
Installation Methods and Construction Details
Proper installation is critical to the performance of any waterstop system. The positioning within the joint varies depending on whether the waterstop is placed at the surface or internally.
Surface Waterstops
Surface water bars are placed at the face of construction joints, contraction joints, movement joints, and expansion joints. The type used for construction joints differs from those specified for expansion and movement joints. When expansion or movement is expected, the middle segment of the water bar is modified with a bulb or loop shape that allows the joint to open and close without tearing the waterstop. Dimensions can vary depending on the supplier and project specifications. External waterproofing membranes applied under foundations should continue uninterrupted across these water bars.
Internal Waterstops
Internal waterstops are positioned at the center of construction, contraction, and movement joints. Center bulb water bars are specified for expansion and movement joints, while standard flat profiles can be used for construction and contraction joints where movement is minimal. PVC waterstops can be welded together when longer lengths are needed or when direction changes are required. The welding process involves heating the overlapping sections and holding them firmly together until a continuous bond forms. This allows water bars to continue in any direction based on the construction layout.
The following numbered steps summarize the general installation procedure for PVC and rubber waterstops in a construction joint:
- Prepare the joint surface by cleaning debris, dust, and laitance.
- Position the waterstop at the correct depth within the joint, centering it for internal placement or aligning it at the face for surface placement.
- Secure the waterstop in place using tie wires or clips attached to the reinforcement cage to prevent displacement during concrete pouring.
- For PVC waterstops, weld intersections and splices by heating the material and pressing sections together until fully bonded.
- Pour the first concrete lift carefully, ensuring the waterstop is fully embedded without voids or honeycombing around it.
- After the first lift cures, exposed waterstop sections must be kept clean and protected from damage before the second pour.
- Pour the second concrete lift, taking care to vibrate the concrete around the waterstop without displacing it.
For a broader perspective on why waterstops are essential across different project types, the article What Is Waterstops Or Waterbars Uses In Construction from Construct Update provides additional context on typical use cases and selection rationales.
Key Takeaways for Waterstop Selection
Selecting the right waterstop requires evaluating several factors specific to the project. Below is a checklist of considerations that engineers and contractors should review before making a final choice.
- Joint type: Expansion and movement joints require flexible waterstops such as PVC or rubber. Construction joints can use metallic or bentonite types.
- Hydrostatic pressure: Higher pressures demand waterstops with proven performance data, such as rubber or copper in hydraulic structures.
- Chemical exposure: Rubber and stainless steel perform best in aggressive chemical environments.
- Movement capacity: Structures subject to seismic activity or thermal movement need waterstops with high elongation and flexibility.
- Installation conditions: PVC is easiest to install and weld on site. Bentonite strips require clean, dry grooves and careful placement.
- Service life: For permanent structures with long design lives, copper or high-quality rubber waterstops provide the best longevity.
- Budget: Mild steel and PVC are the most economical options. Copper and stainless steel are premium choices.
Waterstops are a critical but often overlooked component of durable concrete construction. When selected and installed correctly, they provide decades of reliable watertightness across all types of liquid-retaining structures. Engineers should always verify supplier test certificates and ensure that the chosen waterstop meets the relevant ASTM or local standards before approving installation.