Waterproofing 1,929 views Sep 14, 2017
Membranes for below ground structures

Bentonite, a clay substance which is often generated from the alteration of volcanic ash, is renowned for its water absorption. These properties make it a valuable material for a wide range of uses and applications, particularly as a waterproofing material in construction of belowground structures such as basements.

Bentonite’s availability in the marketplace in various product forms is well-known - it’s been around for hundreds of years. However, the appearance of natural sodium bentonite in Sika BentoShield MAX LM, a fully-bonded, needle-punched membrane and integrated polyethylene flexible laminate, represents a unique offering. The polymer-modified product, which is applied to external surfaces of belowground structures exposed to ground water, is the only bentonite system that’s BBA-approved to BS EN 1928:2000 standard relating to flexible sheets for waterproofing.


The sealing technology of Sika BentoShield MAX LM combines the superior swelling performance of the sodium bentonite with high strength polypropylene geotextiles. The two geotextiles are interlocked by a needle-punching process forcing fibres from the non-woven layer through and beyond the woven layer. This process forms a physical link between the geotextiles and locks the bentonite granules in between, keeping them contained. The system is finished with a polyethylene membrane which is laminated to the back which gives an additional level of protection.

Fully Bonded

During installation, the woven geotextile layer bonds to the fresh concrete due to the non-woven layer that is pulled through and beyond from the needle punching process.
When the polymer-enhanced natural sodium bentonite granules get wet they form a dense waterproof gel protecting the structure.

Sika BentoShield MAX LM is designed for use in belowground construction. It differs from other BBA-accredited geosynthetic clay liners as it contains specially formulated polymers to enhance performance in contaminated land with a high salt concentration. As well as basements, it is used in cut-and-cover tunnels, backfilled walls and in a variety of more demanding applications, depending on whether water is to be kept in or out.

The seams for vertical applications of many bentonite membranes are vulnerable to failure. Sika BentoShield MAX LM laps, however, are sealed with a tape to provide a watertight solution as well as protect against debris and water intrusion during backfilling the system. The seams on horizontal sections can be lapped and protected with a bed of paste created by mixing BentoShield granules with water. Alternatively, tape can be used on higher risk sites.


Sika BentoShield MAX LM can also be post-applied to concrete structures where pre-applying is not possible. The membrane is securely held in place with a robust fixing system.

Tested and approved to the latest industry standards, Sika provides a 10-year guarantee or 15 when it is used as part of a dual system from Sika.

Sika also provides, free of charge:

  • Full specification and detailing support
  • Sika tool box talk training
  • Site support and inspection

Easy to install, flexible and robust, Sika BentoShield MAX LM doesn’t require a primer or protection board. Its ability to mechanically bond with the concrete, which in turn virtually eliminates water tracking in the event of damage, makes it the ideal membrane for belowground structures dependent on retaining long-term watertightness.

By Nick Powell, Sika Waterproofing Business Development Manager


For more information visit: http://www.sikawaterproofing.co.uk/products-systems/sika-bentoshield-max-lm/