Bentonite Waterproofing FAQ

Answers to common questions regarding bentonite

What is Sodium Bentonite?
Sodium bentonite is a yellowish-gray, inorganic and nontoxic natural mineral chiefly found in the Black Hills region of the United States. It consists largely of montmorillonite (aluminum silicate), a highly expansive clay having the unusual characteristics of cohesion, binding, sealing, and thickening. Sodium bentonite originated from volcanic ash, combining with saltwater millions of years ago. The crystal lattice structures of sodium bentonite are much thinner and more easily separated by hydration than those of other clays. When wetted and separated, the surface area of bentonite increases many times. This increased surface area, along with irregular dispersion of the clay platelets, resist water penetration, thus forming a very low permeable barrier.

Will bentonite dry out after being hydrated?
No. Bentonite does not dry out after being hydrated in a below-grade waterproofing application. Bentonite, once wetted, will remain hydrated even when the moisture content in the adjacent soils decrease. This is because bentonite has been forced-dried at 650°F (330°C) to an 8% bonded moisture content from its natural 25-30%. Therefore, bentonite has a great affinity for water, and once mechanically bonded, doesn't let it go.

Will bentonite work in the high saline soils of coastal regions?
Yes. A special bentonite, Volclay CR (Contaminate-Resistant), has been designed to work in soils with high concentrations of salts found in coastal regions. Volclay CR is also resistant to other industrial chemicals that may be in the soils. A simple test of the groundwater from the construction site will produce results indicating whether standard Bentonite or Volclay CR is required for that specific project.

Does bentonite have to be immediately hydrated after backfilling?
No. Bentonite does not have to be fully hydrated upon installation. Like most other waterproofing membranes, bentonite will remain dormant until water comes in contact with the waterproofing. When water does contact it, the bentonite immediately hydrates, forming a low permeable barrier.

For underslab applications, does bentonite require a working mud slab?
No. Bentonite, in most cases, does not require a working mud slab to be installed over. The reason for this is that bentonite does not rely on adhesion to function as a waterproofing membrane. Remember, a mud slab traditionally is made of weak concrete mix and usually cracks. Therefore, you are not adhering the waterproofing to the structural slab, but waterproofing the mud slab, which is typically made of a weak concrete mix and is susceptible to cracking.

Will bentonite work with property line construction?
Yes. Bentonite waterproofing systems are ideal for blind-side property line construction. Simply install bentonite to the retaining wall and pour the concrete in a single-sided form. Typical applications include soldier pile and wood lagging, metal sheet piling, earth and shotcrete retention walls, and concrete cassoin construction.

How soon after the concrete pour can bentonite waterproofing be installed?
Bentonite waterproofing systems can be installed to concrete as soon as the forms are removed. There is no seven to 28-day waiting period. Therefore, the work can be completed sooner and the project can proceed on time.

Can bentonite waterproofing be installed in freezing temperatures?
Yes. Unlike most peel-in-stick and fluid-applied waterproofing membranes, bentonite can be installed when temperatures are below freezing. This allows work to proceed in the winter months on time, as scheduled.

Does CETCO offer a warranty?
Yes. CETCO offers a Hydroshield Warranty covering both labor and material on projects when bentonite geotextile membrane waterproofing systems are installed by one of CETCO's Approved Applicators. The warranty is issued directly to the owner of the project. The typical warranty period is one to five years. Issuance of the warranty requires that a CETCO Approved Applicator install the CETCO waterproofing, that a third party independent inspection service by employed by the Owner to inspect the installation, and that Waterstop-RX be installed in all applicable concrete construction joints. Additionally, if a prefabricated drainage system is required, Aquadrain would be installed to complete the single-source responsibility. For full details and availability in your area please contact CETCO.