You have just purchased a geosynthetic clay liner, known as GCL, to waterproof the bottom of a sanitary landfill, an oxidation pond, a reservoir, or any hydraulic work where auditing requires certifiable impermeability. The key to GCL lies in a layer of sodium bentonite between two geotextiles: when hydrated, the bentonite swells and forms a continuous seal. In this guide, we explain how to install it without ruining the material due to premature exposure.
Product Specifications
GCL is a sandwich-type system with two geotextiles confining a layer of powdered or granular natural sodium bentonite. When hydrated, the bentonite swells up to 15 times its dry volume and forms a continuous impermeable seal. The Dodom range is offered in a single standard configuration sized for hydraulic works and waterproofing projects with contractual auditing requirements.
| Specification | Clay barrier GCL |
|---|---|
| SKU | 537587 |
| Type | Bentonitic geocomposite |
| Core | Natural sodium bentonite |
| Function | Self-sealing impermeable barrier |
| Roll width | 5.8 m (19 ft) |
| Roll length | 40 m (131 ft) |
| Coverage per roll | 232 m² (2497 ft²) |
Step-by-step installation guide
GCL is a sensitive material: the bentonite must remain dry until the exact moment it is covered and confined by its top layer. All work planning revolves around not exposing it to rain or hydrating it prematurely. Follow these steps in strict order.
Prepare the subgrade
Level and compact the surface until it is smooth, firm, and free of sharp objects (stones, roots, debris). Any protruding elements can puncture the GCL when the top layer is placed. The surface must be dry at the time of installation.
Excavate the perimeter anchor trench
Around the perimeter of the area to be waterproofed, dig a trench 50 cm (20 in) deep by 50 cm (20 in) wide. This is the GCL's anchoring point: the edge is buried inside and backfilled with compacted soil. Without this trench, the material will shift during covering.
Unroll the material
Unroll the material perpendicular to the main slope, starting from the highest elevation and working downwards. Handle the material carefully: GCL is heavy when hydrated, but fragile when dry and subject to strong bends. Use a spreader bar or mechanical equipment when possible.
Perform the overlaps
Overlap 30 cm (12 in) at transverse joints and 15 cm (6 in) at longitudinal joints. Spread bentonite powder (300 g/linear meter) between the two overlapping layers before closing it. This extra bentonite is what seals the joint when everything is hydrated. Without it, the overlaps are the weak point of the system.
Anchor the perimeter
Place the edge of the GCL into the perimeter trench, backfill with soil, and compact. If the work connects to concrete structures (walls, spillway, chamber), use Poly Lock or a mechanical system to seal the contact. The GCL-concrete joint is the other critical point for leaks.
Cover within 24 hours
Place the top layer (HDPE geomembrane in composite systems, or at least 30 cm of cover soil in simple systems) on the same day. The bentonite must be confined before it comes into contact with water. Once covered and confined, the natural hydration of the ground progressively activates it.
Plan the installation in sections that can be completed and covered on the same day. If the project is large, divide the area and work on one section each day, leaving the next day's rolls protected in their original packaging. This way, you will never have exposed GCL waiting to be covered when a rainy afternoon arrives.
Do not leave the GCL exposed to rain before covering it. If the bentonite hydrates without being confined, it swells freely, turns into a gel, loses its internal structure, and stops sealing. Once hydrated outside the impermeable sandwich, the material is irrecoverable: the entire affected section must be replaced. No shortcuts.
GCL alone or composite system with HDPE?
For sanitary landfills and works with contractual auditing, a composite system (GCL + HDPE geomembrane) is usually required. For agricultural reservoirs and ponds, GCL alone may be sufficient. Ask the virtual assistant for the appropriate configuration according to the type of work and applicable regulations.
Complementary products
For professional GCL installation in audited hydraulic works, the following complementary products cover the functions of top layer, anchoring to structures, and temporary fixation.
The HDPE polyethylene geomembrane is the upper layer of the mandatory composite system in landfills and projects subject to contractual audit. The Poly Lock solves the sealing of the GCL with concrete structures (landfills, manholes, perimeter walls): it is the only professional way to close the transition between geocomposite and concrete. The anchor cap is used for temporary fixings of the GCL during installation, especially on steep slopes.
Maintenance and care
A properly installed and confined GCL is a long-life system that requires no specific maintenance. Care focuses on prior storage and avoiding subsequent perforations:
- Storage of uninstalled rolls: in a covered place, on pallets, with the original wrapping sealed. Bentonite absorbs environmental moisture: if the rolls get wet in storage, they become unusable before reaching the site.
- Do not walk on bare GCL: the weight of personnel on uncovered rolls compacts the bentonite and creates thinner areas. If you need to cross, use wooden planks as a walkway.
- Document the installation: photographically record each sector covered on the same day. In audited projects, the logbook with photos and times proves that coverage was completed on time.
- Be careful with subsequent nearby works: any subsequent excavation near the waterproofed area can compromise the system. Mark limits on plans and signal them on site.
- Bentonite residue: leftover bentonite powder is not discarded: it is saved for future joint or overlap repairs.
Frequently asked questions
What happens if it rains on the GCL before covering it?
The wet area becomes unusable. The bentonite swells without being confined, turns into gel, and loses its structure. The affected area must be removed and replaced. There is no way to recover prematurely hydrated bentonite. This is why it is critical to plan installation in sections that can be covered on the same day and not have exposed stock on site.
Can I use GCL alone or do I need HDPE geomembrane on top?
It depends on the project and applicable regulations. Sanitary landfills and projects with environmental audits (ISO 14001) usually require a GCL + HDPE geomembrane composite system. Agricultural reservoirs, retention ponds, and less demanding projects can use GCL alone with a soil cover layer. If the project has specifications or a contractual audit, follow what the document states.
How much overlap between rolls should be maintained?
30 cm (12 in) for transverse joints (head-to-head of consecutive rolls in the deployment direction) and 15 cm (6 in) for longitudinal joints (between parallel rolls). In addition to the overlap, spread bentonite powder inside the joint at a rate of 300 g/linear meter. Without this extra bentonite, the overlap is only geotextile to geotextile and does not seal.