Mapei Idrostop B25

Idrostop B25 – Hydro-Expanding Bentonite Waterstop

Idrostop B25 is a pre-formed hydro-expanding bentonite waterstop designed to create watertight construction joints in civil, industrial and hydraulic concrete structures. It is manufactured from natural sodium bentonite and polymers, providing a flexible and stable joint-sealing material.

When Idrostop B25 comes into contact with water, it expands gradually and uniformly. This expansion allows the strip to adapt to the surrounding concrete and seal localised voids, helping prevent water from passing through construction joints. It can be used against both positive and negative water pressure.

Key Benefits

• Hydro-expanding bentonite waterstop
• Designed for watertight concrete construction joints
• Made from natural sodium bentonite and polymers
• Controlled, gradual and uniform expansion
• Creates an active barrier against water
• Suitable for positive and negative water pressure
• Flexible pre-formed strip
• Helps seal localised voids in concrete
• Suitable for civil, industrial and hydraulic construction
• Suitable for joints between different materials
• No waiting period required before concrete casting
• Suitable for application from -5°C to +50°C

Applications

Idrostop B25 is suitable for waterproofing construction and contact joints, including:

• Concrete foundation-to-wall construction joints
• Joints between concrete pours
• Joints between different construction materials
• Steel pipes passing through concrete
• PVC pipes passing through concrete
• Swimming pools
• Water-treatment structures
• Storage tanks and reservoirs
• Hydraulic structures
• Civil and industrial concrete construction
• Sealing elements passing through bentonite waterproofing membranes

Technical Information

• Product type: Hydro-expanding bentonite waterstop
• Form: Pre-formed strip
• Composition: Natural sodium bentonite and polymers
• Dimensions: 20 × 25mm
• Colour: Dark green
• Application temperature: -5°C to +50°C
• Water solubility: Insoluble
• Main property: Expands on contact with water
• Packaging: 6 × 5m rolls per box
• Total per box: 30 linear metres
• Waiting time before concrete casting: Not required
• Storage: 24 months

How Idrostop B25 Works

Idrostop B25 is positioned within the construction joint before the second concrete pour. When water reaches the bentonite strip, it gradually expands and fills available spaces within the joint.

The controlled expansion allows the material to conform to the surrounding concrete and helps close localised voids, creating a barrier against water penetration.

Installation & Important Requirements

The installation surface should be suitable for application and free from standing water. Idrostop B25 should not be installed while the structure is immersed in water.

The substrate should also be free from significant acid or solvent contamination.

Important installation requirements include:

• Idrostop B25 must not be used as a structural expansion joint.
• The boundary distance must be at least 80mm.
• Reinforcement spacers must be positioned at least 50mm from the surface on which Idrostop B25 is installed.
• Follow the manufacturer's installation requirements for positioning and fixing.
• The suitability of the product should be assessed for the specific project and substrate.

Frequently Asked Questions

1. What is Idrostop B25 used for?
Idrostop B25 is used to waterproof construction joints in concrete structures using a hydro-expanding bentonite waterstop.

2. How does Idrostop B25 waterproof a joint?
The natural bentonite within the strip expands when it comes into contact with water. This expansion fills available spaces around the joint and helps prevent water from passing through.

3. What size is Idrostop B25?
Idrostop B25 has a cross-section of 20 × 25mm and is supplied as 5m rolls.

4. How much Idrostop B25 is supplied in a box?
Each box contains 6 × 5m rolls, providing a total of 30 linear metres.

5. Does Idrostop B25 need to expand before concrete is poured?
No. There is no required waiting period before casting the concrete after installation.

Important Limitations

Idrostop B25 should not be installed where there is standing water or while the structure is immersed in water.

It should not be used as a structural expansion joint. The required minimum boundary distance and reinforcement clearance must also be maintained during installation.

Downloads