CLAYTEX: bentonite waterproofing of underground structures

Code: S.0014

"Sheats" waterproofing of underground premises, constantly in contact with the phreatic water, via positioning and correct fastening of the sandwich mats in polypropylene containing 5 kg/m² of sodium bentonite.

Products used

The problem

Waterproofing of underground structures is a significant problem in the foundation engineering field. Water can cause early deterioration of the works both due to the physical effect, due to penetration on the support, and chemical type degradation; in fact, the water is normally a saline solution of chemical agents which can interact and clog the cement matrix of the manufactured pieces.

In any case, the end result is unplanned deterioration and damage of the structures, both in terms of static resistance and functionality of the work. Therefore, it is a fundamental requirement for the underground works to have correct waterproofing which ensures it completely meets the various needs during the entire life of the work.

The solution

A first analysis of the possible solutions for waterproofing underground structures distinguishes between "passive systems", which only fulfils the barrier function by obstructing the structure/fluid and "active systems", capable of interacting with the fluid, inhibiting possible infiltrations, even with the advanced status of the works. Bentonite geo-synthetic barriers belong to this second category. 

A bentonite geo-compound can be defined as a hydraulic barrier composed of a bentonite layer with low permeability, supported using geo-textiles or geo-membranes assembled with different principles. You could think of a "bentonite geo-compound" as a bentonite container; the bentonite composes the waterproofing matrix and the containment geo-textiles the protection element that gives mechanical resistance to the barrier system.

The CLAYTEX bentonite mat

The CLAYTEX mat is composed of two flexible, permeable and needle felted geo-textiles assembled to internally host 5 kg/m² of granular sodium bentonite with a high standard of montmorillonite (over 95%). It is used by confining the mats by "refilling", to position the CLAYTEX mat against the structure, confined by refill materials. The confinement described is used to prevent complete expansion of the sodium bentonite. This causes a glue-like, coherent and waterproof gel to form which is self-sealing and ready for re-activation with further expansion processes in the event of cracks and deformations of the structure.


  • Natural sealant activated by water
  • Self-sealing
  • Porous, protective mats to enable fast hydration
  • Continuous and uniform bentonite layer
  • Flexible
  • Resistant to biological and environmental attacks
  • Does not age over time.


If CLAYTEX is applied directly on the ground or under the structural foundations, the substrate must be well compacted and composed of natural, fine and homogeneous material. On the contrary, it would be useful to have a 7-8 cm thick layer of concrete, when not indispensable. The polypropylene side (the darkest one) should always be turned upwards. Gradually, the CLAYTEX mat is laid and nailed on the concrete substrate, which must be covered with a 5-6 cm layer of concrete to avoid possible damage caused by sudden rain or laying of reinforcement on the next foundation.


The mats should be placed on vertical surfaces starting from the bottom, limiting the excess portions of the "blade" formwork spacers with an abrasive disc, and the subsequent filling to the top of the resulting depression, as well as the PVC tubular spacer hole with OSMOCEM AC anti-carbonation cement mortar 

Un rotolo di CLAYTEX 110Each CLAYTEX mat measures 1.10x5.00 metres and is therefore easily applied using steel nails for walls 5-6 cm and plastic or similar material washers suitable for the purpose. The polypropylene side (the darkest one) should always be turned outwards. The row of lowest mats must be turned around the base of the foundation and fit as perfectly as possible to the inner corners, rounded in advance where possible, using shells built of two-component, osmotic quick setting cement mortar OSMOCEM 447. All adjacent mats should overlap by at least 5 cm. The rows of subsequent mats to the first must be carefully applied to offset the vertical joints. CLAYTEX does not require further protection. If the situation allows, the filler material (sand) must be adequately placed on the mats, in subsequent layers at a maximum height of 60-80 cm, correctly compacted and possibly dampened. If you cannot immediately refill, the dark plastic film can be used as a temporary protection against precipitation. 

The CLAYTEX system is easily applied and requires minimum surface preparation. No primer sub-layer is required; you can lay it on fresh concrete, even if dirty and dusty; it does not require sheets, textiles or other protective materials; the laying incidence is compatible with most drainage systems; there are no restrictions regarding the application temperature.


  • CLAYTEX mats cannot be installed on roofs, tunnels or structural platforms in the absence of an adequate protective covering in the form of at least 20 cm of concrete or 50 cm of earth. 
  • The mats must be protected from rain and water of any origin, for example with polyethylene sheets, until the refill or contrast material is laid.
  • If they are damaged, due to abundant precipitation before using protection devices, the damaged and/or swollen parts must be replaced to re-create correct waterproofing continuity.
  • In the presence of high hydrostatic pressure (over 1 atm) you should install a double layer of mats. 

For installation on brick or cement block walls, you need to firstly plaster the contact surfaces with sand and cement mortar.

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