PP Geomembranes: Applications, Benefits & Installation Guide for Water Tanks
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Solutions & Applications · Geosynthetics
The geomembrane is the only material in the project that must not have a single defect. A geotextile with a defect filters slightly less effectively; a waterproof basement envelope with a single hole will leak. And almost always, the hole was not present on the roll to begin with — it was created on site.
The tray before the membrane
The majority of failures in retention basins are identified before the first roll is unrolled. Three key points regarding earthworks:
- Slope gradient: the steeper the slope, the greater the shear stress at the membrane-soil interface. Stability is not only a matter of the soil but also depends on whether the waterproofing will slide towards the bottom under its own weight and the weight of the water.
- Compaction and levelling: the surface must be cleared of stones, roots, sharp objects and excavation debris. Any angular grain that remains acts as a point of puncture when the water column presses the membrane against it.
- Anchoring trench: a perimeter trench into which the edge of the membrane is inserted and encased. Without it, the membrane is held in place solely by friction against the slope — and the first rainfall or the first strong gust of wind will pull it inwards.
Geotextile is not optional
A protective geotextile is always laid between the ground and the membrane. It is not a filter here — it is a cushion: it distributes the point loads from the grains so that they do not concentrate at a single point on the membrane.
The critical parameter is resistance to static puncture. PNW Protection is the heaviest product in the range, designed specifically for this purpose: CBR up to 14 kN and weights up to 2,000 g/m². In basins with a fine-grained, stabilised sub-base and shallow depth, the NW Standard at 400–600 g/m² is sufficient. Below 400 g/m², the protection is not considered adequate for a geomembrane.
Where backfill is to be placed over the membrane — on ramps, access areas or buried sections — a protective geotextile is also laid on top.
The membrane floats. This is the most underestimated type of water tank failure and occurs when the tank is empty: if the groundwater level rises or if gases from the decomposition of organic matter accumulate beneath the waterproofing, the pressure causes the membrane to form huge blisters, which permanently deform it and often tear it at the seams.
The solution is planned from the outset: an underlying drainage system with an inspection chamber, and ventilation points on the slopes. The second rule is practical and costs nothing: the basin does not empty abruptly — rapid drainage removes the counterbalance before the underlying pressure has had time to dissipate.
Why polypropylene?
| Property | What does ‘in the reservoir’ mean? |
|---|---|
| Exceptional flexibility | Elongation at break in excess of 800 per cent — follows the uneven settlement of the subgrade without tearing. Adapts to irregular slopes and complex geometries without developing stresses — in contrast to more rigid materials that ‘bridge’ voids |
| High chemical resistance | It also covers sewage or industrial waste tanks, not just clean water |
| UV stability | Withstands exposed installation — the reservoir is not covered. Durability in sunlight increases with thickness |
| No plasticisers | There are no plasticisers that leach into water or degrade over time. For drinking water, the relevant certification for the product code is required. |
| Excellent heat-sealing | Enables controlled seams with a double cord and test channel |
Where PVC is preferred, DANOPOL HS provides waterproofing for reservoirs in accordance with EN 13361 and for channels in accordance with EN 13362 — with the difference that, as it is PVC, it contains plasticisers.
The final feature in the table is the most practical. A material that cannot be bonded reliably cannot be inspected reliably — and in a waterproof basement envelope, anything that cannot be inspected is not accepted.
Laying: the mistake of stretching
The geomembrane is laid without excessive tension, with small, controlled folds. The reason for this is thermal: polypropylene contracts and expands significantly with temperature. A sheet laid taut at midday in July will be under tension on a winter’s night — and will fail at its weakest point, which is always the seam.
- Installation time: laying in conditions of extreme heat requires provision for excess material; bonding at very low temperatures requires preheating.
- Wind: unrolled and unsecured sheets must be temporarily secured. Any sheet that has been lifted off must be destroyed.
- Traffic: no vehicles on the membrane without a protective layer.
Thermal bonding and inspection — the stage that determines the success of the project
| Method | Where it is used | How it is checked |
|---|---|---|
| Automatic hot wedge machine | Large, flat surfaces on the base and slopes | Double seam with intermediate channel — compressed air test along the entire length |
| Hand-held hot-air tool | Details, corners, penetrations, repairs | Single seam — vacuum bell test or mechanical pin test |
The difference is not only technical but also conventional: the double seam with a channel allows for non-destructive testing along its entire length, with pressure recording. This is why it is preferred wherever possible, and why the number of manual seams is kept to a minimum when designing the sheet layout.
The PP geomembrane is also available factory-welded to the project’s dimensions. For small and medium-sized catchment areas, this means that most of the seams are formed at the factory — under controlled conditions — before the material reaches the site.
Prior to production welding, the contractor crew carries out test seams under the prevailing conditions of the day — temperature, wind, humidity — and tests them for tensile strength and peel strength. The machine’s parameters are adjusted according to these conditions, not according to a general formula.
Concrete penetrations and connections
Every water intake, overflow or drainage pipe is a hole that must be sealed. The same applies to every point where the membrane comes into contact with a concrete structure — manholes, walls, pump bases.
A water-swelling bentonite cord (waterstop) is used here: it swells when exposed to moisture and seals the construction joint by exerting pressure on its walls. The principle is the opposite of that of a waterproofing membrane — it does not keep water out, but uses it to activate itself.
Where there is a risk of mechanical damage — access zones, maintenance work areas, areas with stones on the upstream slope — a protective HDPE membrane is added over the waterproofing.
Thickness: the only decision that cannot be corrected
The thickness is determined by three parameters taken together, and none of these is the area:
- Hydrostatic load: the depth of the water table determines the pressure exerted by the membrane on the substrate.
- Substrate quality: the coarser-grained and more angular the substrate, the greater the requirement — or the heavier the protective geotextile must be.
- Exposure and service life: a roof exposed to the Greek climate means years of UV exposure and temperature cycles.
| Thickness of PP geomembrane | Weight | Sun resistance |
|---|---|---|
| 500 μm | 450 g/m² | 6 years |
| 750 μm | 675 g/m² | 7–10 years |
| 1000 μm | 900 g/m² | 10 years |
In a permanent, uncovered installation, therefore, thickness is not just a matter of strength — it is a matter of service life.
It is the only aspect of the project that cannot be rectified retrospectively: reinforcing an undersized waterproof basement envelope means draining, removing and rebuilding.
How much membrane is needed — and why not simply the area?
The most common mistake in quantity take-off is to multiply the length by the width of the basin. However, the membrane covers four elements, and only the first is the plan view:
- The floor — the only surface measured from the plan view.
- Slopes — measured along their inclined length, not in their horizontal projection; the gentler the slope, the greater the difference.
- The anchoring trench — the edge of the membrane descends, runs along the bottom of the trench and rises.
- Sheet overlaps and the excess required for the folds in the installation.
The difference between the floor plan area and the actual membrane surface area is not a minor detail — it is often the difference between a project that goes ahead and one that falls through.
The quantity take-off is based on cross-sections — we carry this out ourselves
| What you are sending us | What you get |
|---|---|
| Dimensions of the basin at the crown and at the base | Calculation of membrane area with slopes, trenches and overlaps |
| Depth and slope of embankments | Proposed membrane thickness for the hydrostatic load |
| Use: irrigation, drinking water, fire-fighting, waste | Selection of materials and protective geotextiles |
| Photographs or a description of the ground | Technical and financial quotation for the entire stratification |
Please send us the cross-section or dimensions of the retention tank to info@argynet.gr. We calculate the actual surface area of the membrane and geotextile, recommend thicknesses and provide a quotation for the entire system — membrane, protection and penetration sealing.
Fields of application
- Irrigation reservoirs and water conveyance channels.
- Fire-fighting and liquid storage tanks.
- Artificial lakes and landscape architecture projects.
- Landfill sites — where chemical resistance is a key criterion.
- Aquaculture and fish farm tanks.
Design series
- Use and content: irrigation, drinking water, sewage or waste — specifies materials and certifications prior to any dimensioning.
- Geotechnical aspects: slope gradient, sub-base quality, water table.
- Underlay management: drainage and ventilation beneath the membrane — these should be designed in conjunction with the drainage system, not afterwards.
- Selection of protective geotextile: based on particle size distribution and hydrostatic head.
- Membrane thickness and sheet layout to minimise hand-sewn seams.
- Details: anchor trench, penetrations, connections to concrete, access ramp.
- Test protocol: test seams, channel test, vacuum bell, recording.
Basin Waterproofing
Protection & Sealing
Underlayers & Categories
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Has provision been made for what will happen when the basin empties — and how much membrane is actually required?
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