Intumescent cords for waterproofing seams: bentonite or acrylic

Intumescent cords for waterproofing seams: bentonite or acrylic

To ensure reliable waterproofing of technological joints in concrete structures (cold joints, construction joints, joints of interruption of concreting), it is critically important to use special materials . These materials have the unique property of expanding upon contact with water, creating self-sealing of the joint. Among the most common solutions are swelling cords : bentonite and acrylic .

Although both types of cords have a similar operating principle and end result, their compositions and performance characteristics differ significantly, which affects the choice for specific construction conditions. Understanding this difference is the key to choosing the right waterproofing cord .

Bentonite swelling cord

Bentonite cord consists mainly (about 75% ) of natural bentonite clay . Upon hydration (interaction with water), the clay increases dramatically in volume, turning into a gel-like mass . This mass effectively fills microcracks, voids and gaps in the seam, ensuring high-quality sealing .

Advantages of bentonite cord :

• Pressure resistance: Withstands hydrostatic pressure up to 7 atmospheres .
• Chemical inertness: Well resists aggressive environments.
• Environmental friendliness: Natural, safe composition.
• Easy installation: Does not require high qualifications or specialized equipment. Can be laid on a wet concrete base .
• Affordable price: Low cost compared to acrylic counterparts.

Limitations of bentonite cord :

• Expansion/Compression Cycles: Designed for a limited number of wetting and drying cycles . Frequent cycles may cause delamination of the material.
• Risk of premature swelling: Prolonged contact with moisture before concreting can cause premature swelling .
• Uncontrolled expansion: Under certain conditions, it can cause excessive pressure on the screed, potentially leading to cracking or failure of thin concrete layers.
• Washout: There is a small chance of clay being washed out of the joint cavity at high water flow rates.

Acrylic swelling cord

Acrylic cord is a modern polymer material. Its basis is acrylic polymer with the addition of rubber and synthetic resins . Unlike bentonite, acrylic cord expands in proportion to the amount of water absorbed, which allows for more precise control of the process.

Advantages of a wing cord :

• Unlimited resource: Provides an unlimited number of expansion and compression cycles without loss of properties.
• Reliable fixation: Washing out of the seam cavity is impossible due to the polymer structure.
• Controlled pressure: The expansion process is controlled and depends on the increase in external pressure, which eliminates the risk of cracks and extrusion of the concrete layer.
• Salt and chemical resistance: High resistance to salt water and a variety of chemicals .
• Pressure: Withstands hydrostatic pressure up to 5 atmospheres .

Wing cord limitations :​

• Cost: Has a higher cost compared to bentonite.
• Installation: Installation on a wet surface is prohibited - requires a dry surface for reliable bonding or fixation.

Choosing a swelling cord : bentonite VS acrylic​ ​​​

The choice between bentonite and acrylic swelling cord should be based on a thorough analysis of the technical specifications and operating conditions of the facility.

When to choose bentonite cord? If the main criteria are price and high pressure resistance (up to 7 atm), and the object does not involve constant wetting/drying cycles, bentonite cord is ideal.

When to choose acrylic cord? If maximum durability is required, the object is subject to frequent humidity cycles, a guarantee against leaching and a controlled expansion process are required (especially for thin structures), it is worth choosing acrylic cord.

For professional waterproofing of objects of any complexity, PROTEX offers a wide range of high-quality swelling cords . Contact our specialists for detailed advice and selection of the optimal waterproofing solution for your concrete structures.