EPDM geomembrane and stone carpet: how a lagoon pool stays watertight

A free form cannot be poured into formwork. To make it watertight, we use an EPDM geomembrane, a flexible membrane that follows every curve, with a stone carpet finish (moquette de pierre). Here is how it works, and what makes the difference on site.

The principle

The pool is dug to the exact shape of the project: the curves, the submerged shallow area, the changes of depth. Waterproofing is provided by an EPDM geomembrane, and the stone carpet finish gives the lagoon pool its mineral look.

What is EPDM?

EPDM (ethylene propylene diene monomer) is a synthetic rubber. As a geomembrane, it has long been used to make ponds, basins and water reservoirs watertight.

Its main quality for a lagoon pool: it is flexible. It follows the curves and slopes of the free form, where rigid formwork would impose straight lines.

The connections: where watertightness is decided

The surface of the membrane rarely causes problems. The weak points are elsewhere:

• The parts that pass through it: skimmers, return inlets, lights.
• The corners and changes of slope, where the membrane must be fitted without tension.
• The waterline, permanently exposed to the alternation of air and water.

That is where you can tell a well-done installation.

The stone carpet finish

The finish, a stone carpet, gives the lagoon pool its natural look. It is a covering made of mineral aggregates, such as marble or quartz, bound with resin. For outdoor use, a polyurethane resin is generally recommended, as it resists UV better than an epoxy resin.

Its surface is textured, and its colour depends on the shade of the aggregates chosen.

What still needs watching

Like any covering, it needs to be treated with care: no pointed metal tools for cleaning, no heavy or sharp objects dragged across the bottom of the pool. And as with any pool, well-balanced water is kinder to coverings and equipment. We cover all of this in maintaining a lagoon pool in the Marrakech climate.

Questions to ask your builder

• Which membrane, and how thick?
• How is the base prepared before laying?
• How are the connections made around skimmers, inlets and lights?
• Which resin for the finish, and for what use?

A serious builder answers these questions straightforwardly, and shows you these stages on site.