Short answer: choose a bentonite swell bar for construction joints that will sit permanently below the groundwater table, and a hydrophilic swell bar where the joint may alternate between wet and dry, may get wet before it is covered, or needs a controlled, repeatable swell. For critical structures, pair either one with a re-injectable injection hose as a second line of defence.
What does a swell bar do?
A swell bar (also called a swellable waterstop or water-swelling strip) is fixed along a concrete construction joint, the line where one pour meets the next. Concrete shrinks as it cures, so these joints often contain fine gaps and honeycombing that let groundwater through. When water reaches the swell bar, it expands inside the confined joint, fills those voids and blocks the leakage path.
Both bentonite and hydrophilic swell bars work this way. The difference is what swells and how it behaves over time.
How does a bentonite swell bar work?
A bentonite swell bar is made from natural sodium bentonite clay. On contact with water the clay hydrates and expands, forming a dense, low-permeability gel that seals the joint and resists hydrostatic pressure. Bentonite performs best when it stays in contact with water, which is why it is common in basements, sumps, underground tanks and foundations below the water table.
How does a hydrophilic swell bar work?
A hydrophilic swell bar is made from a water-absorbing polymer. Maruti's grades expand by 300–700% of their original volume on contact with water, depending on the grade selected. The swelling is reversible: when the joint dries out the bar shrinks back, and it swells again the next time water arrives. That makes it well suited to joints exposed to fluctuating water levels, and to sites where the bar might get wet during construction. Maruti's hydrophilic swell bar carries a DMRC approval for metro works.
Bentonite vs hydrophilic swell bar: side-by-side
| Factor | Bentonite swell bar | Hydrophilic swell bar |
|---|---|---|
| Swelling material | Natural sodium bentonite clay | Hydrophilic (water-absorbing) polymer |
| Best water condition | Continuous contact with groundwater | Wet/dry cycles or fluctuating water levels |
| Swelling behaviour | Hydrates into a dense clay gel | Controlled, reversible expansion (300–700% for Maruti grades) |
| Sensitivity to early wetting | High: must be kept dry until concreted | Lower: designed to tolerate repeated wetting |
| Typical uses | Basements, sumps, water tanks, foundations below the water table | Metro and tunnel joints, water-retaining structures, joints near the water-table line |
| Approvals (Maruti) | Manufactured under ISO 9001:2015 / ISO 14001:2015 | DMRC approval; ISO 9001:2015 / ISO 14001:2015 |
Which one should you choose?
- Permanently saturated ground (deep basements, sumps, tanks below the water table): bentonite swell bar is a proven, economical choice.
- Fluctuating water table, splash zones or monsoon-exposed pours: hydrophilic swell bar, because it recovers after drying and is less sensitive to getting wet before it is covered.
- Metro stations, tunnels and high-risk structures: a hydrophilic swell bar with DMRC approval, backed up by an injection hose so the joint can be grouted later if needed.
- Expansion joints and joints with large movement: neither swell bar alone. Use a cast-in PVC water stop seal with a centre-bulb profile.
Installation tips that decide whether a swell bar works
- Fix the bar to a clean, sound concrete surface near the centre of the joint so it cannot move or float during the next pour.
- Keep adequate concrete cover on both sides, as specified by the designer. A bar placed too close to the face can spall the concrete as it swells.
- Protect bentonite bars from rain and standing water until they are cast in.
- Butt or overlap the ends with no gaps; a single gap is a leakage path.
- Where the consequences of a leak are high, add a re-injectable grouting tube alongside the swell bar.
Where to buy swell bars in India
Maruti Techno Rubber Pvt. Ltd. has manufactured waterproofing products since 1982 and introduced its hydrophilic swell bar in 2008. We supply both bentonite and hydrophilic swell bars factory-direct from Greater Noida to projects across India, including Chennai, Hyderabad, Madhya Pradesh, Bihar, West Bengal and the North East. See where we supply on our Supply Across India page, or request a quote with your joint length and site conditions.
